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Diffstat (limited to 'Documentation/technical')
45 files changed, 5660 insertions, 147 deletions
diff --git a/Documentation/technical/.gitignore b/Documentation/technical/.gitignore new file mode 100644 index 0000000000..8aa891daee --- /dev/null +++ b/Documentation/technical/.gitignore @@ -0,0 +1 @@ +api-index.txt diff --git a/Documentation/technical/api-allocation-growing.txt b/Documentation/technical/api-allocation-growing.txt new file mode 100644 index 0000000000..5a59b54844 --- /dev/null +++ b/Documentation/technical/api-allocation-growing.txt @@ -0,0 +1,39 @@ +allocation growing API +====================== + +Dynamically growing an array using realloc() is error prone and boring. + +Define your array with: + +* a pointer (`item`) that points at the array, initialized to `NULL` + (although please name the variable based on its contents, not on its + type); + +* an integer variable (`alloc`) that keeps track of how big the current + allocation is, initialized to `0`; + +* another integer variable (`nr`) to keep track of how many elements the + array currently has, initialized to `0`. + +Then before adding `n`th element to the item, call `ALLOC_GROW(item, n, +alloc)`. This ensures that the array can hold at least `n` elements by +calling `realloc(3)` and adjusting `alloc` variable. + +------------ +sometype *item; +size_t nr; +size_t alloc + +for (i = 0; i < nr; i++) + if (we like item[i] already) + return; + +/* we did not like any existing one, so add one */ +ALLOC_GROW(item, nr + 1, alloc); +item[nr++] = value you like; +------------ + +You are responsible for updating the `nr` variable. + +If you need to specify the number of elements to allocate explicitly +then use the macro `REALLOC_ARRAY(item, alloc)` instead of `ALLOC_GROW`. diff --git a/Documentation/technical/api-argv-array.txt b/Documentation/technical/api-argv-array.txt new file mode 100644 index 0000000000..1a797812fb --- /dev/null +++ b/Documentation/technical/api-argv-array.txt @@ -0,0 +1,55 @@ +argv-array API +============== + +The argv-array API allows one to dynamically build and store +NULL-terminated lists. An argv-array maintains the invariant that the +`argv` member always points to a non-NULL array, and that the array is +always NULL-terminated at the element pointed to by `argv[argc]`. This +makes the result suitable for passing to functions expecting to receive +argv from main(), or the link:api-run-command.html[run-command API]. + +The link:api-string-list.html[string-list API] is similar, but cannot be +used for these purposes; instead of storing a straight string pointer, +it contains an item structure with a `util` field that is not compatible +with the traditional argv interface. + +Each `argv_array` manages its own memory. Any strings pushed into the +array are duplicated, and all memory is freed by argv_array_clear(). + +Data Structures +--------------- + +`struct argv_array`:: + + A single array. This should be initialized by assignment from + `ARGV_ARRAY_INIT`, or by calling `argv_array_init`. The `argv` + member contains the actual array; the `argc` member contains the + number of elements in the array, not including the terminating + NULL. + +Functions +--------- + +`argv_array_init`:: + Initialize an array. This is no different than assigning from + `ARGV_ARRAY_INIT`. + +`argv_array_push`:: + Push a copy of a string onto the end of the array. + +`argv_array_pushl`:: + Push a list of strings onto the end of the array. The arguments + should be a list of `const char *` strings, terminated by a NULL + argument. + +`argv_array_pushf`:: + Format a string and push it onto the end of the array. This is a + convenience wrapper combining `strbuf_addf` and `argv_array_push`. + +`argv_array_pop`:: + Remove the final element from the array. If there are no + elements in the array, do nothing. + +`argv_array_clear`:: + Free all memory associated with the array and return it to the + initial, empty state. diff --git a/Documentation/technical/api-builtin.txt b/Documentation/technical/api-builtin.txt new file mode 100644 index 0000000000..22a39b9299 --- /dev/null +++ b/Documentation/technical/api-builtin.txt @@ -0,0 +1,73 @@ +builtin API +=========== + +Adding a new built-in +--------------------- + +There are 4 things to do to add a built-in command implementation to +Git: + +. Define the implementation of the built-in command `foo` with + signature: + + int cmd_foo(int argc, const char **argv, const char *prefix); + +. Add the external declaration for the function to `builtin.h`. + +. Add the command to the `commands[]` table defined in `git.c`. + The entry should look like: + + { "foo", cmd_foo, <options> }, ++ +where options is the bitwise-or of: + +`RUN_SETUP`:: + If there is not a Git directory to work on, abort. If there + is a work tree, chdir to the top of it if the command was + invoked in a subdirectory. If there is no work tree, no + chdir() is done. + +`RUN_SETUP_GENTLY`:: + If there is a Git directory, chdir as per RUN_SETUP, otherwise, + don't chdir anywhere. + +`USE_PAGER`:: + + If the standard output is connected to a tty, spawn a pager and + feed our output to it. + +`NEED_WORK_TREE`:: + + Make sure there is a work tree, i.e. the command cannot act + on bare repositories. + This only makes sense when `RUN_SETUP` is also set. + +. Add `builtin/foo.o` to `BUILTIN_OBJS` in `Makefile`. + +Additionally, if `foo` is a new command, there are 3 more things to do: + +. Add tests to `t/` directory. + +. Write documentation in `Documentation/git-foo.txt`. + +. Add an entry for `git-foo` to `command-list.txt`. + +. Add an entry for `/git-foo` to `.gitignore`. + + +How a built-in is called +------------------------ + +The implementation `cmd_foo()` takes three parameters, `argc`, `argv, +and `prefix`. The first two are similar to what `main()` of a +standalone command would be called with. + +When `RUN_SETUP` is specified in the `commands[]` table, and when you +were started from a subdirectory of the work tree, `cmd_foo()` is called +after chdir(2) to the top of the work tree, and `prefix` gets the path +to the subdirectory the command started from. This allows you to +convert a user-supplied pathname (typically relative to that directory) +to a pathname relative to the top of the work tree. + +The return value from `cmd_foo()` becomes the exit status of the +command. diff --git a/Documentation/technical/api-config.txt b/Documentation/technical/api-config.txt new file mode 100644 index 0000000000..0d8b99b368 --- /dev/null +++ b/Documentation/technical/api-config.txt @@ -0,0 +1,324 @@ +config API +========== + +The config API gives callers a way to access Git configuration files +(and files which have the same syntax). See linkgit:git-config[1] for a +discussion of the config file syntax. + +General Usage +------------- + +Config files are parsed linearly, and each variable found is passed to a +caller-provided callback function. The callback function is responsible +for any actions to be taken on the config option, and is free to ignore +some options. It is not uncommon for the configuration to be parsed +several times during the run of a Git program, with different callbacks +picking out different variables useful to themselves. + +A config callback function takes three parameters: + +- the name of the parsed variable. This is in canonical "flat" form: the + section, subsection, and variable segments will be separated by dots, + and the section and variable segments will be all lowercase. E.g., + `core.ignorecase`, `diff.SomeType.textconv`. + +- the value of the found variable, as a string. If the variable had no + value specified, the value will be NULL (typically this means it + should be interpreted as boolean true). + +- a void pointer passed in by the caller of the config API; this can + contain callback-specific data + +A config callback should return 0 for success, or -1 if the variable +could not be parsed properly. + +Basic Config Querying +--------------------- + +Most programs will simply want to look up variables in all config files +that Git knows about, using the normal precedence rules. To do this, +call `git_config` with a callback function and void data pointer. + +`git_config` will read all config sources in order of increasing +priority. Thus a callback should typically overwrite previously-seen +entries with new ones (e.g., if both the user-wide `~/.gitconfig` and +repo-specific `.git/config` contain `color.ui`, the config machinery +will first feed the user-wide one to the callback, and then the +repo-specific one; by overwriting, the higher-priority repo-specific +value is left at the end). + +The `git_config_with_options` function lets the caller examine config +while adjusting some of the default behavior of `git_config`. It should +almost never be used by "regular" Git code that is looking up +configuration variables. It is intended for advanced callers like +`git-config`, which are intentionally tweaking the normal config-lookup +process. It takes two extra parameters: + +`filename`:: +If this parameter is non-NULL, it specifies the name of a file to +parse for configuration, rather than looking in the usual files. Regular +`git_config` defaults to `NULL`. + +`respect_includes`:: +Specify whether include directives should be followed in parsed files. +Regular `git_config` defaults to `1`. + +There is a special version of `git_config` called `git_config_early`. +This version takes an additional parameter to specify the repository +config, instead of having it looked up via `git_path`. This is useful +early in a Git program before the repository has been found. Unless +you're working with early setup code, you probably don't want to use +this. + +Reading Specific Files +---------------------- + +To read a specific file in git-config format, use +`git_config_from_file`. This takes the same callback and data parameters +as `git_config`. + +Querying For Specific Variables +------------------------------- + +For programs wanting to query for specific variables in a non-callback +manner, the config API provides two functions `git_config_get_value` +and `git_config_get_value_multi`. They both read values from an internal +cache generated previously from reading the config files. + +`int git_config_get_value(const char *key, const char **value)`:: + + Finds the highest-priority value for the configuration variable `key`, + stores the pointer to it in `value` and returns 0. When the + configuration variable `key` is not found, returns 1 without touching + `value`. The caller should not free or modify `value`, as it is owned + by the cache. + +`const struct string_list *git_config_get_value_multi(const char *key)`:: + + Finds and returns the value list, sorted in order of increasing priority + for the configuration variable `key`. When the configuration variable + `key` is not found, returns NULL. The caller should not free or modify + the returned pointer, as it is owned by the cache. + +`void git_config_clear(void)`:: + + Resets and invalidates the config cache. + +The config API also provides type specific API functions which do conversion +as well as retrieval for the queried variable, including: + +`int git_config_get_int(const char *key, int *dest)`:: + + Finds and parses the value to an integer for the configuration variable + `key`. Dies on error; otherwise, stores the value of the parsed integer in + `dest` and returns 0. When the configuration variable `key` is not found, + returns 1 without touching `dest`. + +`int git_config_get_ulong(const char *key, unsigned long *dest)`:: + + Similar to `git_config_get_int` but for unsigned longs. + +`int git_config_get_bool(const char *key, int *dest)`:: + + Finds and parses the value into a boolean value, for the configuration + variable `key` respecting keywords like "true" and "false". Integer + values are converted into true/false values (when they are non-zero or + zero, respectively). Other values cause a die(). If parsing is successful, + stores the value of the parsed result in `dest` and returns 0. When the + configuration variable `key` is not found, returns 1 without touching + `dest`. + +`int git_config_get_bool_or_int(const char *key, int *is_bool, int *dest)`:: + + Similar to `git_config_get_bool`, except that integers are copied as-is, + and `is_bool` flag is unset. + +`int git_config_get_maybe_bool(const char *key, int *dest)`:: + + Similar to `git_config_get_bool`, except that it returns -1 on error + rather than dying. + +`int git_config_get_string_const(const char *key, const char **dest)`:: + + Allocates and copies the retrieved string into the `dest` parameter for + the configuration variable `key`; if NULL string is given, prints an + error message and returns -1. When the configuration variable `key` is + not found, returns 1 without touching `dest`. + +`int git_config_get_string(const char *key, char **dest)`:: + + Similar to `git_config_get_string_const`, except that retrieved value + copied into the `dest` parameter is a mutable string. + +`int git_config_get_pathname(const char *key, const char **dest)`:: + + Similar to `git_config_get_string`, but expands `~` or `~user` into + the user's home directory when found at the beginning of the path. + +`git_die_config(const char *key, const char *err, ...)`:: + + First prints the error message specified by the caller in `err` and then + dies printing the line number and the file name of the highest priority + value for the configuration variable `key`. + +`void git_die_config_linenr(const char *key, const char *filename, int linenr)`:: + + Helper function which formats the die error message according to the + parameters entered. Used by `git_die_config()`. It can be used by callers + handling `git_config_get_value_multi()` to print the correct error message + for the desired value. + +See test-config.c for usage examples. + +Value Parsing Helpers +--------------------- + +To aid in parsing string values, the config API provides callbacks with +a number of helper functions, including: + +`git_config_int`:: +Parse the string to an integer, including unit factors. Dies on error; +otherwise, returns the parsed result. + +`git_config_ulong`:: +Identical to `git_config_int`, but for unsigned longs. + +`git_config_bool`:: +Parse a string into a boolean value, respecting keywords like "true" and +"false". Integer values are converted into true/false values (when they +are non-zero or zero, respectively). Other values cause a die(). If +parsing is successful, the return value is the result. + +`git_config_bool_or_int`:: +Same as `git_config_bool`, except that integers are returned as-is, and +an `is_bool` flag is unset. + +`git_config_maybe_bool`:: +Same as `git_config_bool`, except that it returns -1 on error rather +than dying. + +`git_config_string`:: +Allocates and copies the value string into the `dest` parameter; if no +string is given, prints an error message and returns -1. + +`git_config_pathname`:: +Similar to `git_config_string`, but expands `~` or `~user` into the +user's home directory when found at the beginning of the path. + +Include Directives +------------------ + +By default, the config parser does not respect include directives. +However, a caller can use the special `git_config_include` wrapper +callback to support them. To do so, you simply wrap your "real" callback +function and data pointer in a `struct config_include_data`, and pass +the wrapper to the regular config-reading functions. For example: + +------------------------------------------- +int read_file_with_include(const char *file, config_fn_t fn, void *data) +{ + struct config_include_data inc = CONFIG_INCLUDE_INIT; + inc.fn = fn; + inc.data = data; + return git_config_from_file(git_config_include, file, &inc); +} +------------------------------------------- + +`git_config` respects includes automatically. The lower-level +`git_config_from_file` does not. + +Custom Configsets +----------------- + +A `config_set` can be used to construct an in-memory cache for +config-like files that the caller specifies (i.e., files like `.gitmodules`, +`~/.gitconfig` etc.). For example, + +--------------------------------------- +struct config_set gm_config; +git_configset_init(&gm_config); +int b; +/* we add config files to the config_set */ +git_configset_add_file(&gm_config, ".gitmodules"); +git_configset_add_file(&gm_config, ".gitmodules_alt"); + +if (!git_configset_get_bool(gm_config, "submodule.frotz.ignore", &b)) { + /* hack hack hack */ +} + +/* when we are done with the configset */ +git_configset_clear(&gm_config); +---------------------------------------- + +Configset API provides functions for the above mentioned work flow, including: + +`void git_configset_init(struct config_set *cs)`:: + + Initializes the config_set `cs`. + +`int git_configset_add_file(struct config_set *cs, const char *filename)`:: + + Parses the file and adds the variable-value pairs to the `config_set`, + dies if there is an error in parsing the file. Returns 0 on success, or + -1 if the file does not exist or is inaccessible. The user has to decide + if he wants to free the incomplete configset or continue using it when + the function returns -1. + +`int git_configset_get_value(struct config_set *cs, const char *key, const char **value)`:: + + Finds the highest-priority value for the configuration variable `key` + and config set `cs`, stores the pointer to it in `value` and returns 0. + When the configuration variable `key` is not found, returns 1 without + touching `value`. The caller should not free or modify `value`, as it + is owned by the cache. + +`const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key)`:: + + Finds and returns the value list, sorted in order of increasing priority + for the configuration variable `key` and config set `cs`. When the + configuration variable `key` is not found, returns NULL. The caller + should not free or modify the returned pointer, as it is owned by the cache. + +`void git_configset_clear(struct config_set *cs)`:: + + Clears `config_set` structure, removes all saved variable-value pairs. + +In addition to above functions, the `config_set` API provides type specific +functions in the vein of `git_config_get_int` and family but with an extra +parameter, pointer to struct `config_set`. +They all behave similarly to the `git_config_get*()` family described in +"Querying For Specific Variables" above. + +Writing Config Files +-------------------- + +Git gives multiple entry points in the Config API to write config values to +files namely `git_config_set_in_file` and `git_config_set`, which write to +a specific config file or to `.git/config` respectively. They both take a +key/value pair as parameter. +In the end they both call `git_config_set_multivar_in_file` which takes four +parameters: + +- the name of the file, as a string, to which key/value pairs will be written. + +- the name of key, as a string. This is in canonical "flat" form: the section, + subsection, and variable segments will be separated by dots, and the section + and variable segments will be all lowercase. + E.g., `core.ignorecase`, `diff.SomeType.textconv`. + +- the value of the variable, as a string. If value is equal to NULL, it will + remove the matching key from the config file. + +- the value regex, as a string. It will disregard key/value pairs where value + does not match. + +- a multi_replace value, as an int. If value is equal to zero, nothing or only + one matching key/value is replaced, else all matching key/values (regardless + how many) are removed, before the new pair is written. + +It returns 0 on success. + +Also, there are functions `git_config_rename_section` and +`git_config_rename_section_in_file` with parameters `old_name` and `new_name` +for renaming or removing sections in the config files. If NULL is passed +through `new_name` parameter, the section will be removed from the config file. diff --git a/Documentation/technical/api-credentials.txt b/Documentation/technical/api-credentials.txt new file mode 100644 index 0000000000..e44426dd04 --- /dev/null +++ b/Documentation/technical/api-credentials.txt @@ -0,0 +1,271 @@ +credentials API +=============== + +The credentials API provides an abstracted way of gathering username and +password credentials from the user (even though credentials in the wider +world can take many forms, in this document the word "credential" always +refers to a username and password pair). + +This document describes two interfaces: the C API that the credential +subsystem provides to the rest of Git, and the protocol that Git uses to +communicate with system-specific "credential helpers". If you are +writing Git code that wants to look up or prompt for credentials, see +the section "C API" below. If you want to write your own helper, see +the section on "Credential Helpers" below. + +Typical setup +------------- + +------------ ++-----------------------+ +| Git code (C) |--- to server requiring ---> +| | authentication +|.......................| +| C credential API |--- prompt ---> User ++-----------------------+ + ^ | + | pipe | + | v ++-----------------------+ +| Git credential helper | ++-----------------------+ +------------ + +The Git code (typically a remote-helper) will call the C API to obtain +credential data like a login/password pair (credential_fill). The +API will itself call a remote helper (e.g. "git credential-cache" or +"git credential-store") that may retrieve credential data from a +store. If the credential helper cannot find the information, the C API +will prompt the user. Then, the caller of the API takes care of +contacting the server, and does the actual authentication. + +C API +----- + +The credential C API is meant to be called by Git code which needs to +acquire or store a credential. It is centered around an object +representing a single credential and provides three basic operations: +fill (acquire credentials by calling helpers and/or prompting the user), +approve (mark a credential as successfully used so that it can be stored +for later use), and reject (mark a credential as unsuccessful so that it +can be erased from any persistent storage). + +Data Structures +~~~~~~~~~~~~~~~ + +`struct credential`:: + + This struct represents a single username/password combination + along with any associated context. All string fields should be + heap-allocated (or NULL if they are not known or not applicable). + The meaning of the individual context fields is the same as + their counterparts in the helper protocol; see the section below + for a description of each field. ++ +The `helpers` member of the struct is a `string_list` of helpers. Each +string specifies an external helper which will be run, in order, to +either acquire or store credentials. See the section on credential +helpers below. This list is filled-in by the API functions +according to the corresponding configuration variables before +consulting helpers, so there usually is no need for a caller to +modify the helpers field at all. ++ +This struct should always be initialized with `CREDENTIAL_INIT` or +`credential_init`. + + +Functions +~~~~~~~~~ + +`credential_init`:: + + Initialize a credential structure, setting all fields to empty. + +`credential_clear`:: + + Free any resources associated with the credential structure, + returning it to a pristine initialized state. + +`credential_fill`:: + + Instruct the credential subsystem to fill the username and + password fields of the passed credential struct by first + consulting helpers, then asking the user. After this function + returns, the username and password fields of the credential are + guaranteed to be non-NULL. If an error occurs, the function will + die(). + +`credential_reject`:: + + Inform the credential subsystem that the provided credentials + have been rejected. This will cause the credential subsystem to + notify any helpers of the rejection (which allows them, for + example, to purge the invalid credentials from storage). It + will also free() the username and password fields of the + credential and set them to NULL (readying the credential for + another call to `credential_fill`). Any errors from helpers are + ignored. + +`credential_approve`:: + + Inform the credential subsystem that the provided credentials + were successfully used for authentication. This will cause the + credential subsystem to notify any helpers of the approval, so + that they may store the result to be used again. Any errors + from helpers are ignored. + +`credential_from_url`:: + + Parse a URL into broken-down credential fields. + +Example +~~~~~~~ + +The example below shows how the functions of the credential API could be +used to login to a fictitious "foo" service on a remote host: + +----------------------------------------------------------------------- +int foo_login(struct foo_connection *f) +{ + int status; + /* + * Create a credential with some context; we don't yet know the + * username or password. + */ + + struct credential c = CREDENTIAL_INIT; + c.protocol = xstrdup("foo"); + c.host = xstrdup(f->hostname); + + /* + * Fill in the username and password fields by contacting + * helpers and/or asking the user. The function will die if it + * fails. + */ + credential_fill(&c); + + /* + * Otherwise, we have a username and password. Try to use it. + */ + status = send_foo_login(f, c.username, c.password); + switch (status) { + case FOO_OK: + /* It worked. Store the credential for later use. */ + credential_accept(&c); + break; + case FOO_BAD_LOGIN: + /* Erase the credential from storage so we don't try it + * again. */ + credential_reject(&c); + break; + default: + /* + * Some other error occurred. We don't know if the + * credential is good or bad, so report nothing to the + * credential subsystem. + */ + } + + /* Free any associated resources. */ + credential_clear(&c); + + return status; +} +----------------------------------------------------------------------- + + +Credential Helpers +------------------ + +Credential helpers are programs executed by Git to fetch or save +credentials from and to long-term storage (where "long-term" is simply +longer than a single Git process; e.g., credentials may be stored +in-memory for a few minutes, or indefinitely on disk). + +Each helper is specified by a single string in the configuration +variable `credential.helper` (and others, see linkgit:git-config[1]). +The string is transformed by Git into a command to be executed using +these rules: + + 1. If the helper string begins with "!", it is considered a shell + snippet, and everything after the "!" becomes the command. + + 2. Otherwise, if the helper string begins with an absolute path, the + verbatim helper string becomes the command. + + 3. Otherwise, the string "git credential-" is prepended to the helper + string, and the result becomes the command. + +The resulting command then has an "operation" argument appended to it +(see below for details), and the result is executed by the shell. + +Here are some example specifications: + +---------------------------------------------------- +# run "git credential-foo" +foo + +# same as above, but pass an argument to the helper +foo --bar=baz + +# the arguments are parsed by the shell, so use shell +# quoting if necessary +foo --bar="whitespace arg" + +# you can also use an absolute path, which will not use the git wrapper +/path/to/my/helper --with-arguments + +# or you can specify your own shell snippet +!f() { echo "password=`cat $HOME/.secret`"; }; f +---------------------------------------------------- + +Generally speaking, rule (3) above is the simplest for users to specify. +Authors of credential helpers should make an effort to assist their +users by naming their program "git-credential-$NAME", and putting it in +the $PATH or $GIT_EXEC_PATH during installation, which will allow a user +to enable it with `git config credential.helper $NAME`. + +When a helper is executed, it will have one "operation" argument +appended to its command line, which is one of: + +`get`:: + + Return a matching credential, if any exists. + +`store`:: + + Store the credential, if applicable to the helper. + +`erase`:: + + Remove a matching credential, if any, from the helper's storage. + +The details of the credential will be provided on the helper's stdin +stream. The exact format is the same as the input/output format of the +`git credential` plumbing command (see the section `INPUT/OUTPUT +FORMAT` in linkgit:git-credential[7] for a detailed specification). + +For a `get` operation, the helper should produce a list of attributes +on stdout in the same format. A helper is free to produce a subset, or +even no values at all if it has nothing useful to provide. Any provided +attributes will overwrite those already known about by Git. If a helper +outputs a `quit` attribute with a value of `true` or `1`, no further +helpers will be consulted, nor will the user be prompted (if no +credential has been provided, the operation will then fail). + +For a `store` or `erase` operation, the helper's output is ignored. +If it fails to perform the requested operation, it may complain to +stderr to inform the user. If it does not support the requested +operation (e.g., a read-only store), it should silently ignore the +request. + +If a helper receives any other operation, it should silently ignore the +request. This leaves room for future operations to be added (older +helpers will just ignore the new requests). + +See also +-------- + +linkgit:gitcredentials[7] + +linkgit:git-config[5] (See configuration variables `credential.*`) diff --git a/Documentation/technical/api-decorate.txt b/Documentation/technical/api-decorate.txt new file mode 100644 index 0000000000..1d52a6ce14 --- /dev/null +++ b/Documentation/technical/api-decorate.txt @@ -0,0 +1,6 @@ +decorate API +============ + +Talk about <decorate.h> + +(Linus) diff --git a/Documentation/technical/api-diff.txt b/Documentation/technical/api-diff.txt new file mode 100644 index 0000000000..8b001de0db --- /dev/null +++ b/Documentation/technical/api-diff.txt @@ -0,0 +1,174 @@ +diff API +======== + +The diff API is for programs that compare two sets of files (e.g. two +trees, one tree and the index) and present the found difference in +various ways. The calling program is responsible for feeding the API +pairs of files, one from the "old" set and the corresponding one from +"new" set, that are different. The library called through this API is +called diffcore, and is responsible for two things. + +* finding total rewrites (`-B`), renames (`-M`) and copies (`-C`), and + changes that touch a string (`-S`), as specified by the caller. + +* outputting the differences in various formats, as specified by the + caller. + +Calling sequence +---------------- + +* Prepare `struct diff_options` to record the set of diff options, and + then call `diff_setup()` to initialize this structure. This sets up + the vanilla default. + +* Fill in the options structure to specify desired output format, rename + detection, etc. `diff_opt_parse()` can be used to parse options given + from the command line in a way consistent with existing git-diff + family of programs. + +* Call `diff_setup_done()`; this inspects the options set up so far for + internal consistency and make necessary tweaking to it (e.g. if + textual patch output was asked, recursive behaviour is turned on); + the callback set_default in diff_options can be used to tweak this more. + +* As you find different pairs of files, call `diff_change()` to feed + modified files, `diff_addremove()` to feed created or deleted files, + or `diff_unmerge()` to feed a file whose state is 'unmerged' to the + API. These are thin wrappers to a lower-level `diff_queue()` function + that is flexible enough to record any of these kinds of changes. + +* Once you finish feeding the pairs of files, call `diffcore_std()`. + This will tell the diffcore library to go ahead and do its work. + +* Calling `diff_flush()` will produce the output. + + +Data structures +--------------- + +* `struct diff_filespec` + +This is the internal representation for a single file (blob). It +records the blob object name (if known -- for a work tree file it +typically is a NUL SHA-1), filemode and pathname. This is what the +`diff_addremove()`, `diff_change()` and `diff_unmerge()` synthesize and +feed `diff_queue()` function with. + +* `struct diff_filepair` + +This records a pair of `struct diff_filespec`; the filespec for a file +in the "old" set (i.e. preimage) is called `one`, and the filespec for a +file in the "new" set (i.e. postimage) is called `two`. A change that +represents file creation has NULL in `one`, and file deletion has NULL +in `two`. + +A `filepair` starts pointing at `one` and `two` that are from the same +filename, but `diffcore_std()` can break pairs and match component +filespecs with other filespecs from a different filepair to form new +filepair. This is called 'rename detection'. + +* `struct diff_queue` + +This is a collection of filepairs. Notable members are: + +`queue`:: + + An array of pointers to `struct diff_filepair`. This + dynamically grows as you add filepairs; + +`alloc`:: + + The allocated size of the `queue` array; + +`nr`:: + + The number of elements in the `queue` array. + + +* `struct diff_options` + +This describes the set of options the calling program wants to affect +the operation of diffcore library with. + +Notable members are: + +`output_format`:: + The output format used when `diff_flush()` is run. + +`context`:: + Number of context lines to generate in patch output. + +`break_opt`, `detect_rename`, `rename-score`, `rename_limit`:: + Affects the way detection logic for complete rewrites, renames + and copies. + +`abbrev`:: + Number of hexdigits to abbreviate raw format output to. + +`pickaxe`:: + A constant string (can and typically does contain newlines to + look for a block of text, not just a single line) to filter out + the filepairs that do not change the number of strings contained + in its preimage and postimage of the diff_queue. + +`flags`:: + This is mostly a collection of boolean options that affects the + operation, but some do not have anything to do with the diffcore + library. + +`touched_flags`:: + Records whether a flag has been changed due to user request + (rather than just set/unset by default). + +`set_default`:: + Callback which allows tweaking the options in diff_setup_done(). + +BINARY, TEXT;; + Affects the way how a file that is seemingly binary is treated. + +FULL_INDEX;; + Tells the patch output format not to use abbreviated object + names on the "index" lines. + +FIND_COPIES_HARDER;; + Tells the diffcore library that the caller is feeding unchanged + filepairs to allow copies from unmodified files be detected. + +COLOR_DIFF;; + Output should be colored. + +COLOR_DIFF_WORDS;; + Output is a colored word-diff. + +NO_INDEX;; + Tells diff-files that the input is not tracked files but files + in random locations on the filesystem. + +ALLOW_EXTERNAL;; + Tells output routine that it is Ok to call user specified patch + output routine. Plumbing disables this to ensure stable output. + +QUIET;; + Do not show any output. + +REVERSE_DIFF;; + Tells the library that the calling program is feeding the + filepairs reversed; `one` is two, and `two` is one. + +EXIT_WITH_STATUS;; + For communication between the calling program and the options + parser; tell the calling program to signal the presence of + difference using program exit code. + +HAS_CHANGES;; + Internal; used for optimization to see if there is any change. + +SILENT_ON_REMOVE;; + Affects if diff-files shows removed files. + +RECURSIVE, TREE_IN_RECURSIVE;; + Tells if tree traversal done by tree-diff should recursively + descend into a tree object pair that are different in preimage + and postimage set. + +(JC) diff --git a/Documentation/technical/api-directory-listing.txt b/Documentation/technical/api-directory-listing.txt new file mode 100644 index 0000000000..7f8e78d916 --- /dev/null +++ b/Documentation/technical/api-directory-listing.txt @@ -0,0 +1,105 @@ +directory listing API +===================== + +The directory listing API is used to enumerate paths in the work tree, +optionally taking `.git/info/exclude` and `.gitignore` files per +directory into account. + +Data structure +-------------- + +`struct dir_struct` structure is used to pass directory traversal +options to the library and to record the paths discovered. A single +`struct dir_struct` is used regardless of whether or not the traversal +recursively descends into subdirectories. + +The notable options are: + +`exclude_per_dir`:: + + The name of the file to be read in each directory for excluded + files (typically `.gitignore`). + +`flags`:: + + A bit-field of options (the `*IGNORED*` flags are mutually exclusive): + +`DIR_SHOW_IGNORED`::: + + Return just ignored files in `entries[]`, not untracked files. + +`DIR_SHOW_IGNORED_TOO`::: + + Similar to `DIR_SHOW_IGNORED`, but return ignored files in `ignored[]` + in addition to untracked files in `entries[]`. + +`DIR_COLLECT_IGNORED`::: + + Special mode for git-add. Return ignored files in `ignored[]` and + untracked files in `entries[]`. Only returns ignored files that match + pathspec exactly (no wildcards). Does not recurse into ignored + directories. + +`DIR_SHOW_OTHER_DIRECTORIES`::: + + Include a directory that is not tracked. + +`DIR_HIDE_EMPTY_DIRECTORIES`::: + + Do not include a directory that is not tracked and is empty. + +`DIR_NO_GITLINKS`::: + + If set, recurse into a directory that looks like a Git + directory. Otherwise it is shown as a directory. + +The result of the enumeration is left in these fields: + +`entries[]`:: + + An array of `struct dir_entry`, each element of which describes + a path. + +`nr`:: + + The number of members in `entries[]` array. + +`alloc`:: + + Internal use; keeps track of allocation of `entries[]` array. + +`ignored[]`:: + + An array of `struct dir_entry`, used for ignored paths with the + `DIR_SHOW_IGNORED_TOO` and `DIR_COLLECT_IGNORED` flags. + +`ignored_nr`:: + + The number of members in `ignored[]` array. + +Calling sequence +---------------- + +Note: index may be looked at for .gitignore files that are CE_SKIP_WORKTREE +marked. If you to exclude files, make sure you have loaded index first. + +* Prepare `struct dir_struct dir` and clear it with `memset(&dir, 0, + sizeof(dir))`. + +* To add single exclude pattern, call `add_exclude_list()` and then + `add_exclude()`. + +* To add patterns from a file (e.g. `.git/info/exclude`), call + `add_excludes_from_file()` , and/or set `dir.exclude_per_dir`. A + short-hand function `setup_standard_excludes()` can be used to set + up the standard set of exclude settings. + +* Set options described in the Data Structure section above. + +* Call `read_directory()`. + +* Use `dir.entries[]`. + +* Call `clear_directory()` when none of the contained elements are no longer in use. + +(JC) diff --git a/Documentation/technical/api-error-handling.txt b/Documentation/technical/api-error-handling.txt new file mode 100644 index 0000000000..ceeedd485c --- /dev/null +++ b/Documentation/technical/api-error-handling.txt @@ -0,0 +1,75 @@ +Error reporting in git +====================== + +`die`, `usage`, `error`, and `warning` report errors of various +kinds. + +- `die` is for fatal application errors. It prints a message to + the user and exits with status 128. + +- `usage` is for errors in command line usage. After printing its + message, it exits with status 129. (See also `usage_with_options` + in the link:api-parse-options.html[parse-options API].) + +- `error` is for non-fatal library errors. It prints a message + to the user and returns -1 for convenience in signaling the error + to the caller. + +- `warning` is for reporting situations that probably should not + occur but which the user (and Git) can continue to work around + without running into too many problems. Like `error`, it + returns -1 after reporting the situation to the caller. + +Customizable error handlers +--------------------------- + +The default behavior of `die` and `error` is to write a message to +stderr and then exit or return as appropriate. This behavior can be +overridden using `set_die_routine` and `set_error_routine`. For +example, "git daemon" uses set_die_routine to write the reason `die` +was called to syslog before exiting. + +Library errors +-------------- + +Functions return a negative integer on error. Details beyond that +vary from function to function: + +- Some functions return -1 for all errors. Others return a more + specific value depending on how the caller might want to react + to the error. + +- Some functions report the error to stderr with `error`, + while others leave that for the caller to do. + +- errno is not meaningful on return from most functions (except + for thin wrappers for system calls). + +Check the function's API documentation to be sure. + +Caller-handled errors +--------------------- + +An increasing number of functions take a parameter 'struct strbuf *err'. +On error, such functions append a message about what went wrong to the +'err' strbuf. The message is meant to be complete enough to be passed +to `die` or `error` as-is. For example: + + if (ref_transaction_commit(transaction, &err)) + die("%s", err.buf); + +The 'err' parameter will be untouched if no error occurred, so multiple +function calls can be chained: + + t = ref_transaction_begin(&err); + if (!t || + ref_transaction_update(t, "HEAD", ..., &err) || + ret_transaction_commit(t, &err)) + die("%s", err.buf); + +The 'err' parameter must be a pointer to a valid strbuf. To silence +a message, pass a strbuf that is explicitly ignored: + + if (thing_that_can_fail_in_an_ignorable_way(..., &err)) + /* This failure is okay. */ + strbuf_reset(&err); diff --git a/Documentation/technical/api-gitattributes.txt b/Documentation/technical/api-gitattributes.txt new file mode 100644 index 0000000000..2602668677 --- /dev/null +++ b/Documentation/technical/api-gitattributes.txt @@ -0,0 +1,128 @@ +gitattributes API +================= + +gitattributes mechanism gives a uniform way to associate various +attributes to set of paths. + + +Data Structure +-------------- + +`struct git_attr`:: + + An attribute is an opaque object that is identified by its name. + Pass the name to `git_attr()` function to obtain the object of + this type. The internal representation of this structure is + of no interest to the calling programs. The name of the + attribute can be retrieved by calling `git_attr_name()`. + +`struct git_attr_check`:: + + This structure represents a set of attributes to check in a call + to `git_check_attr()` function, and receives the results. + + +Attribute Values +---------------- + +An attribute for a path can be in one of four states: Set, Unset, +Unspecified or set to a string, and `.value` member of `struct +git_attr_check` records it. There are three macros to check these: + +`ATTR_TRUE()`:: + + Returns true if the attribute is Set for the path. + +`ATTR_FALSE()`:: + + Returns true if the attribute is Unset for the path. + +`ATTR_UNSET()`:: + + Returns true if the attribute is Unspecified for the path. + +If none of the above returns true, `.value` member points at a string +value of the attribute for the path. + + +Querying Specific Attributes +---------------------------- + +* Prepare an array of `struct git_attr_check` to define the list of + attributes you would want to check. To populate this array, you would + need to define necessary attributes by calling `git_attr()` function. + +* Call `git_check_attr()` to check the attributes for the path. + +* Inspect `git_attr_check` structure to see how each of the attribute in + the array is defined for the path. + + +Example +------- + +To see how attributes "crlf" and "indent" are set for different paths. + +. Prepare an array of `struct git_attr_check` with two elements (because + we are checking two attributes). Initialize their `attr` member with + pointers to `struct git_attr` obtained by calling `git_attr()`: + +------------ +static struct git_attr_check check[2]; +static void setup_check(void) +{ + if (check[0].attr) + return; /* already done */ + check[0].attr = git_attr("crlf"); + check[1].attr = git_attr("ident"); +} +------------ + +. Call `git_check_attr()` with the prepared array of `struct git_attr_check`: + +------------ + const char *path; + + setup_check(); + git_check_attr(path, ARRAY_SIZE(check), check); +------------ + +. Act on `.value` member of the result, left in `check[]`: + +------------ + const char *value = check[0].value; + + if (ATTR_TRUE(value)) { + The attribute is Set, by listing only the name of the + attribute in the gitattributes file for the path. + } else if (ATTR_FALSE(value)) { + The attribute is Unset, by listing the name of the + attribute prefixed with a dash - for the path. + } else if (ATTR_UNSET(value)) { + The attribute is neither set nor unset for the path. + } else if (!strcmp(value, "input")) { + If none of ATTR_TRUE(), ATTR_FALSE(), or ATTR_UNSET() is + true, the value is a string set in the gitattributes + file for the path by saying "attr=value". + } else if (... other check using value as string ...) { + ... + } +------------ + + +Querying All Attributes +----------------------- + +To get the values of all attributes associated with a file: + +* Call `git_all_attrs()`, which returns an array of `git_attr_check` + structures. + +* Iterate over the `git_attr_check` array to examine the attribute + names and values. The name of the attribute described by a + `git_attr_check` object can be retrieved via + `git_attr_name(check[i].attr)`. (Please note that no items will be + returned for unset attributes, so `ATTR_UNSET()` will return false + for all returned `git_array_check` objects.) + +* Free the `git_array_check` array. diff --git a/Documentation/technical/api-grep.txt b/Documentation/technical/api-grep.txt new file mode 100644 index 0000000000..a69cc8964d --- /dev/null +++ b/Documentation/technical/api-grep.txt @@ -0,0 +1,8 @@ +grep API +======== + +Talk about <grep.h>, things like: + +* grep_buffer() + +(JC) diff --git a/Documentation/technical/api-hashmap.txt b/Documentation/technical/api-hashmap.txt new file mode 100644 index 0000000000..ad7a5bddd2 --- /dev/null +++ b/Documentation/technical/api-hashmap.txt @@ -0,0 +1,280 @@ +hashmap API +=========== + +The hashmap API is a generic implementation of hash-based key-value mappings. + +Data Structures +--------------- + +`struct hashmap`:: + + The hash table structure. Members can be used as follows, but should + not be modified directly: ++ +The `size` member keeps track of the total number of entries (0 means the +hashmap is empty). ++ +`tablesize` is the allocated size of the hash table. A non-0 value indicates +that the hashmap is initialized. It may also be useful for statistical purposes +(i.e. `size / tablesize` is the current load factor). ++ +`cmpfn` stores the comparison function specified in `hashmap_init()`. In +advanced scenarios, it may be useful to change this, e.g. to switch between +case-sensitive and case-insensitive lookup. + +`struct hashmap_entry`:: + + An opaque structure representing an entry in the hash table, which must + be used as first member of user data structures. Ideally it should be + followed by an int-sized member to prevent unused memory on 64-bit + systems due to alignment. ++ +The `hash` member is the entry's hash code and the `next` member points to the +next entry in case of collisions (i.e. if multiple entries map to the same +bucket). + +`struct hashmap_iter`:: + + An iterator structure, to be used with hashmap_iter_* functions. + +Types +----- + +`int (*hashmap_cmp_fn)(const void *entry, const void *entry_or_key, const void *keydata)`:: + + User-supplied function to test two hashmap entries for equality. Shall + return 0 if the entries are equal. ++ +This function is always called with non-NULL `entry` / `entry_or_key` +parameters that have the same hash code. When looking up an entry, the `key` +and `keydata` parameters to hashmap_get and hashmap_remove are always passed +as second and third argument, respectively. Otherwise, `keydata` is NULL. + +Functions +--------- + +`unsigned int strhash(const char *buf)`:: +`unsigned int strihash(const char *buf)`:: +`unsigned int memhash(const void *buf, size_t len)`:: +`unsigned int memihash(const void *buf, size_t len)`:: + + Ready-to-use hash functions for strings, using the FNV-1 algorithm (see + http://www.isthe.com/chongo/tech/comp/fnv). ++ +`strhash` and `strihash` take 0-terminated strings, while `memhash` and +`memihash` operate on arbitrary-length memory. ++ +`strihash` and `memihash` are case insensitive versions. + +`unsigned int sha1hash(const unsigned char *sha1)`:: + + Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code + for use in hash tables. Cryptographic hashes are supposed to have + uniform distribution, so in contrast to `memhash()`, this just copies + the first `sizeof(int)` bytes without shuffling any bits. Note that + the results will be different on big-endian and little-endian + platforms, so they should not be stored or transferred over the net. + +`void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function, size_t initial_size)`:: + + Initializes a hashmap structure. ++ +`map` is the hashmap to initialize. ++ +The `equals_function` can be specified to compare two entries for equality. +If NULL, entries are considered equal if their hash codes are equal. ++ +If the total number of entries is known in advance, the `initial_size` +parameter may be used to preallocate a sufficiently large table and thus +prevent expensive resizing. If 0, the table is dynamically resized. + +`void hashmap_free(struct hashmap *map, int free_entries)`:: + + Frees a hashmap structure and allocated memory. ++ +`map` is the hashmap to free. ++ +If `free_entries` is true, each hashmap_entry in the map is freed as well +(using stdlib's free()). + +`void hashmap_entry_init(void *entry, unsigned int hash)`:: + + Initializes a hashmap_entry structure. ++ +`entry` points to the entry to initialize. ++ +`hash` is the hash code of the entry. + +`void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)`:: + + Returns the hashmap entry for the specified key, or NULL if not found. ++ +`map` is the hashmap structure. ++ +`key` is a hashmap_entry structure (or user data structure that starts with +hashmap_entry) that has at least been initialized with the proper hash code +(via `hashmap_entry_init`). ++ +If an entry with matching hash code is found, `key` and `keydata` are passed +to `hashmap_cmp_fn` to decide whether the entry matches the key. + +`void *hashmap_get_from_hash(const struct hashmap *map, unsigned int hash, const void *keydata)`:: + + Returns the hashmap entry for the specified hash code and key data, + or NULL if not found. ++ +`map` is the hashmap structure. ++ +`hash` is the hash code of the entry to look up. ++ +If an entry with matching hash code is found, `keydata` is passed to +`hashmap_cmp_fn` to decide whether the entry matches the key. The +`entry_or_key` parameter points to a bogus hashmap_entry structure that +should not be used in the comparison. + +`void *hashmap_get_next(const struct hashmap *map, const void *entry)`:: + + Returns the next equal hashmap entry, or NULL if not found. This can be + used to iterate over duplicate entries (see `hashmap_add`). ++ +`map` is the hashmap structure. ++ +`entry` is the hashmap_entry to start the search from, obtained via a previous +call to `hashmap_get` or `hashmap_get_next`. + +`void hashmap_add(struct hashmap *map, void *entry)`:: + + Adds a hashmap entry. This allows to add duplicate entries (i.e. + separate values with the same key according to hashmap_cmp_fn). ++ +`map` is the hashmap structure. ++ +`entry` is the entry to add. + +`void *hashmap_put(struct hashmap *map, void *entry)`:: + + Adds or replaces a hashmap entry. If the hashmap contains duplicate + entries equal to the specified entry, only one of them will be replaced. ++ +`map` is the hashmap structure. ++ +`entry` is the entry to add or replace. ++ +Returns the replaced entry, or NULL if not found (i.e. the entry was added). + +`void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)`:: + + Removes a hashmap entry matching the specified key. If the hashmap + contains duplicate entries equal to the specified key, only one of + them will be removed. ++ +`map` is the hashmap structure. ++ +`key` is a hashmap_entry structure (or user data structure that starts with +hashmap_entry) that has at least been initialized with the proper hash code +(via `hashmap_entry_init`). ++ +If an entry with matching hash code is found, `key` and `keydata` are +passed to `hashmap_cmp_fn` to decide whether the entry matches the key. ++ +Returns the removed entry, or NULL if not found. + +`void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)`:: +`void *hashmap_iter_next(struct hashmap_iter *iter)`:: +`void *hashmap_iter_first(struct hashmap *map, struct hashmap_iter *iter)`:: + + Used to iterate over all entries of a hashmap. ++ +`hashmap_iter_init` initializes a `hashmap_iter` structure. ++ +`hashmap_iter_next` returns the next hashmap_entry, or NULL if there are no +more entries. ++ +`hashmap_iter_first` is a combination of both (i.e. initializes the iterator +and returns the first entry, if any). + +`const char *strintern(const char *string)`:: +`const void *memintern(const void *data, size_t len)`:: + + Returns the unique, interned version of the specified string or data, + similar to the `String.intern` API in Java and .NET, respectively. + Interned strings remain valid for the entire lifetime of the process. ++ +Can be used as `[x]strdup()` or `xmemdupz` replacement, except that interned +strings / data must not be modified or freed. ++ +Interned strings are best used for short strings with high probability of +duplicates. ++ +Uses a hashmap to store the pool of interned strings. + +Usage example +------------- + +Here's a simple usage example that maps long keys to double values. +------------ +struct hashmap map; + +struct long2double { + struct hashmap_entry ent; /* must be the first member! */ + long key; + double value; +}; + +static int long2double_cmp(const struct long2double *e1, const struct long2double *e2, const void *unused) +{ + return !(e1->key == e2->key); +} + +void long2double_init(void) +{ + hashmap_init(&map, (hashmap_cmp_fn) long2double_cmp, 0); +} + +void long2double_free(void) +{ + hashmap_free(&map, 1); +} + +static struct long2double *find_entry(long key) +{ + struct long2double k; + hashmap_entry_init(&k, memhash(&key, sizeof(long))); + k.key = key; + return hashmap_get(&map, &k, NULL); +} + +double get_value(long key) +{ + struct long2double *e = find_entry(key); + return e ? e->value : 0; +} + +void set_value(long key, double value) +{ + struct long2double *e = find_entry(key); + if (!e) { + e = malloc(sizeof(struct long2double)); + hashmap_entry_init(e, memhash(&key, sizeof(long))); + e->key = key; + hashmap_add(&map, e); + } + e->value = value; +} +------------ + +Using variable-sized keys +------------------------- + +The `hashmap_entry_get` and `hashmap_entry_remove` functions expect an ordinary +`hashmap_entry` structure as key to find the correct entry. If the key data is +variable-sized (e.g. a FLEX_ARRAY string) or quite large, it is undesirable +to create a full-fledged entry structure on the heap and copy all the key data +into the structure. + +In this case, the `keydata` parameter can be used to pass +variable-sized key data directly to the comparison function, and the `key` +parameter can be a stripped-down, fixed size entry structure allocated on the +stack. + +See test-hashmap.c for an example using arbitrary-length strings as keys. diff --git a/Documentation/technical/api-history-graph.txt b/Documentation/technical/api-history-graph.txt new file mode 100644 index 0000000000..18142b6d29 --- /dev/null +++ b/Documentation/technical/api-history-graph.txt @@ -0,0 +1,174 @@ +history graph API +================= + +The graph API is used to draw a text-based representation of the commit +history. The API generates the graph in a line-by-line fashion. + +Functions +--------- + +Core functions: + +* `graph_init()` creates a new `struct git_graph` + +* `graph_update()` moves the graph to a new commit. + +* `graph_next_line()` outputs the next line of the graph into a strbuf. It + does not add a terminating newline. + +* `graph_padding_line()` outputs a line of vertical padding in the graph. It + is similar to `graph_next_line()`, but is guaranteed to never print the line + containing the current commit. Where `graph_next_line()` would print the + commit line next, `graph_padding_line()` prints a line that simply extends + all branch lines downwards one row, leaving their positions unchanged. + +* `graph_is_commit_finished()` determines if the graph has output all lines + necessary for the current commit. If `graph_update()` is called before all + lines for the current commit have been printed, the next call to + `graph_next_line()` will output an ellipsis, to indicate that a portion of + the graph was omitted. + +The following utility functions are wrappers around `graph_next_line()` and +`graph_is_commit_finished()`. They always print the output to stdout. +They can all be called with a NULL graph argument, in which case no graph +output will be printed. + +* `graph_show_commit()` calls `graph_next_line()` and + `graph_is_commit_finished()` until one of them return non-zero. This prints + all graph lines up to, and including, the line containing this commit. + Output is printed to stdout. The last line printed does not contain a + terminating newline. + +* `graph_show_oneline()` calls `graph_next_line()` and prints the result to + stdout. The line printed does not contain a terminating newline. + +* `graph_show_padding()` calls `graph_padding_line()` and prints the result to + stdout. The line printed does not contain a terminating newline. + +* `graph_show_remainder()` calls `graph_next_line()` until + `graph_is_commit_finished()` returns non-zero. Output is printed to stdout. + The last line printed does not contain a terminating newline. Returns 1 if + output was printed, and 0 if no output was necessary. + +* `graph_show_strbuf()` prints the specified strbuf to stdout, prefixing all + lines but the first with a graph line. The caller is responsible for + ensuring graph output for the first line has already been printed to stdout. + (This can be done with `graph_show_commit()` or `graph_show_oneline()`.) If + a NULL graph is supplied, the strbuf is printed as-is. + +* `graph_show_commit_msg()` is similar to `graph_show_strbuf()`, but it also + prints the remainder of the graph, if more lines are needed after the strbuf + ends. It is better than directly calling `graph_show_strbuf()` followed by + `graph_show_remainder()` since it properly handles buffers that do not end in + a terminating newline. The output printed by `graph_show_commit_msg()` will + end in a newline if and only if the strbuf ends in a newline. + +Data structure +-------------- +`struct git_graph` is an opaque data type used to store the current graph +state. + +Calling sequence +---------------- + +* Create a `struct git_graph` by calling `graph_init()`. When using the + revision walking API, this is done automatically by `setup_revisions()` if + the '--graph' option is supplied. + +* Use the revision walking API to walk through a group of contiguous commits. + The `get_revision()` function automatically calls `graph_update()` each time + it is invoked. + +* For each commit, call `graph_next_line()` repeatedly, until + `graph_is_commit_finished()` returns non-zero. Each call go + `graph_next_line()` will output a single line of the graph. The resulting + lines will not contain any newlines. `graph_next_line()` returns 1 if the + resulting line contains the current commit, or 0 if this is merely a line + needed to adjust the graph before or after the current commit. This return + value can be used to determine where to print the commit summary information + alongside the graph output. + +Limitations +----------- + +* `graph_update()` must be called with commits in topological order. It should + not be called on a commit if it has already been invoked with an ancestor of + that commit, or the graph output will be incorrect. + +* `graph_update()` must be called on a contiguous group of commits. If + `graph_update()` is called on a particular commit, it should later be called + on all parents of that commit. Parents must not be skipped, or the graph + output will appear incorrect. ++ +`graph_update()` may be used on a pruned set of commits only if the parent list +has been rewritten so as to include only ancestors from the pruned set. + +* The graph API does not currently support reverse commit ordering. In + order to implement reverse ordering, the graphing API needs an + (efficient) mechanism to find the children of a commit. + +Sample usage +------------ + +------------ +struct commit *commit; +struct git_graph *graph = graph_init(opts); + +while ((commit = get_revision(opts)) != NULL) { + graph_update(graph, commit); + while (!graph_is_commit_finished(graph)) + { + struct strbuf sb; + int is_commit_line; + + strbuf_init(&sb, 0); + is_commit_line = graph_next_line(graph, &sb); + fputs(sb.buf, stdout); + + if (is_commit_line) + log_tree_commit(opts, commit); + else + putchar(opts->diffopt.line_termination); + } +} +------------ + +Sample output +------------- + +The following is an example of the output from the graph API. This output does +not include any commit summary information--callers are responsible for +outputting that information, if desired. + +------------ +* +* +* +|\ +* | +| | * +| \ \ +| \ \ +*-. \ \ +|\ \ \ \ +| | * | | +| | | | | * +| | | | | * +| | | | | * +| | | | | |\ +| | | | | | * +| * | | | | | +| | | | | * \ +| | | | | |\ | +| | | | * | | | +| | | | * | | | +* | | | | | | | +| |/ / / / / / +|/| / / / / / +* | | | | | | +|/ / / / / / +* | | | | | +| | | | | * +| | | | |/ +| | | | * +------------ diff --git a/Documentation/technical/api-in-core-index.txt b/Documentation/technical/api-in-core-index.txt new file mode 100644 index 0000000000..adbdbf5d75 --- /dev/null +++ b/Documentation/technical/api-in-core-index.txt @@ -0,0 +1,21 @@ +in-core index API +================= + +Talk about <read-cache.c> and <cache-tree.c>, things like: + +* cache -> the_index macros +* read_index() +* write_index() +* ie_match_stat() and ie_modified(); how they are different and when to + use which. +* index_name_pos() +* remove_index_entry_at() +* remove_file_from_index() +* add_file_to_index() +* add_index_entry() +* refresh_index() +* discard_index() +* cache_tree_invalidate_path() +* cache_tree_update() + +(JC, Linus) diff --git a/Documentation/technical/api-index-skel.txt b/Documentation/technical/api-index-skel.txt new file mode 100644 index 0000000000..eda8c195c1 --- /dev/null +++ b/Documentation/technical/api-index-skel.txt @@ -0,0 +1,13 @@ +Git API Documents +================= + +Git has grown a set of internal API over time. This collection +documents them. + +//////////////////////////////////////////////////////////////// +// table of contents begin +//////////////////////////////////////////////////////////////// + +//////////////////////////////////////////////////////////////// +// table of contents end +//////////////////////////////////////////////////////////////// diff --git a/Documentation/technical/api-index.sh b/Documentation/technical/api-index.sh new file mode 100755 index 0000000000..9c3f4131b8 --- /dev/null +++ b/Documentation/technical/api-index.sh @@ -0,0 +1,28 @@ +#!/bin/sh + +( + c=//////////////////////////////////////////////////////////////// + skel=api-index-skel.txt + sed -e '/^\/\/ table of contents begin/q' "$skel" + echo "$c" + + ls api-*.txt | + while read filename + do + case "$filename" in + api-index-skel.txt | api-index.txt) continue ;; + esac + title=$(sed -e 1q "$filename") + html=${filename%.txt}.html + echo "* link:$html[$title]" + done + echo "$c" + sed -n -e '/^\/\/ table of contents end/,$p' "$skel" +) >api-index.txt+ + +if test -f api-index.txt && cmp api-index.txt api-index.txt+ >/dev/null +then + rm -f api-index.txt+ +else + mv api-index.txt+ api-index.txt +fi diff --git a/Documentation/technical/api-lockfile.txt b/Documentation/technical/api-lockfile.txt new file mode 100644 index 0000000000..93b5f23e4c --- /dev/null +++ b/Documentation/technical/api-lockfile.txt @@ -0,0 +1,220 @@ +lockfile API +============ + +The lockfile API serves two purposes: + +* Mutual exclusion and atomic file updates. When we want to change a + file, we create a lockfile `<filename>.lock`, write the new file + contents into it, and then rename the lockfile to its final + destination `<filename>`. We create the `<filename>.lock` file with + `O_CREAT|O_EXCL` so that we can notice and fail if somebody else has + already locked the file, then atomically rename the lockfile to its + final destination to commit the changes and unlock the file. + +* Automatic cruft removal. If the program exits after we lock a file + but before the changes have been committed, we want to make sure + that we remove the lockfile. This is done by remembering the + lockfiles we have created in a linked list and setting up an + `atexit(3)` handler and a signal handler that clean up the + lockfiles. This mechanism ensures that outstanding lockfiles are + cleaned up if the program exits (including when `die()` is called) + or if the program dies on a signal. + +Please note that lockfiles only block other writers. Readers do not +block, but they are guaranteed to see either the old contents of the +file or the new contents of the file (assuming that the filesystem +implements `rename(2)` atomically). + + +Calling sequence +---------------- + +The caller: + +* Allocates a `struct lock_file` either as a static variable or on the + heap, initialized to zeros. Once you use the structure to call the + `hold_lock_file_*` family of functions, it belongs to the lockfile + subsystem and its storage must remain valid throughout the life of + the program (i.e. you cannot use an on-stack variable to hold this + structure). + +* Attempts to create a lockfile by passing that variable and the path + of the final destination (e.g. `$GIT_DIR/index`) to + `hold_lock_file_for_update` or `hold_lock_file_for_append`. + +* Writes new content for the destination file by either: + + * writing to the file descriptor returned by the `hold_lock_file_*` + functions (also available via `lock->fd`). + + * calling `fdopen_lock_file` to get a `FILE` pointer for the open + file and writing to the file using stdio. + +When finished writing, the caller can: + +* Close the file descriptor and rename the lockfile to its final + destination by calling `commit_lock_file` or `commit_lock_file_to`. + +* Close the file descriptor and remove the lockfile by calling + `rollback_lock_file`. + +* Close the file descriptor without removing or renaming the lockfile + by calling `close_lock_file`, and later call `commit_lock_file`, + `commit_lock_file_to`, `rollback_lock_file`, or `reopen_lock_file`. + +Even after the lockfile is committed or rolled back, the `lock_file` +object must not be freed or altered by the caller. However, it may be +reused; just pass it to another call of `hold_lock_file_for_update` or +`hold_lock_file_for_append`. + +If the program exits before you have called one of `commit_lock_file`, +`commit_lock_file_to`, `rollback_lock_file`, or `close_lock_file`, an +`atexit(3)` handler will close and remove the lockfile, rolling back +any uncommitted changes. + +If you need to close the file descriptor you obtained from a +`hold_lock_file_*` function yourself, do so by calling +`close_lock_file`. You should never call `close(2)` or `fclose(3)` +yourself! Otherwise the `struct lock_file` structure would still think +that the file descriptor needs to be closed, and a commit or rollback +would result in duplicate calls to `close(2)`. Worse yet, if you close +and then later open another file descriptor for a completely different +purpose, then a commit or rollback might close that unrelated file +descriptor. + + +Error handling +-------------- + +The `hold_lock_file_*` functions return a file descriptor on success +or -1 on failure (unless `LOCK_DIE_ON_ERROR` is used; see below). On +errors, `errno` describes the reason for failure. Errors can be +reported by passing `errno` to one of the following helper functions: + +unable_to_lock_message:: + + Append an appropriate error message to a `strbuf`. + +unable_to_lock_error:: + + Emit an appropriate error message using `error()`. + +unable_to_lock_die:: + + Emit an appropriate error message and `die()`. + +Similarly, `commit_lock_file`, `commit_lock_file_to`, and +`close_lock_file` return 0 on success. On failure they set `errno` +appropriately, do their best to roll back the lockfile, and return -1. + + +Flags +----- + +The following flags can be passed to `hold_lock_file_for_update` or +`hold_lock_file_for_append`: + +LOCK_NO_DEREF:: + + Usually symbolic links in the destination path are resolved + and the lockfile is created by adding ".lock" to the resolved + path. If `LOCK_NO_DEREF` is set, then the lockfile is created + by adding ".lock" to the path argument itself. This option is + used, for example, when locking a symbolic reference, which + for backwards-compatibility reasons can be a symbolic link + containing the name of the referred-to-reference. + +LOCK_DIE_ON_ERROR:: + + If a lock is already taken for the file, `die()` with an error + message. If this option is not specified, trying to lock a + file that is already locked returns -1 to the caller. + + +The functions +------------- + +hold_lock_file_for_update:: + + Take a pointer to `struct lock_file`, the path of the file to + be locked (e.g. `$GIT_DIR/index`) and a flags argument (see + above). Attempt to create a lockfile for the destination and + return the file descriptor for writing to the file. + +hold_lock_file_for_append:: + + Like `hold_lock_file_for_update`, but before returning copy + the existing contents of the file (if any) to the lockfile and + position its write pointer at the end of the file. + +fdopen_lock_file:: + + Associate a stdio stream with the lockfile. Return NULL + (*without* rolling back the lockfile) on error. The stream is + closed automatically when `close_lock_file` is called or when + the file is committed or rolled back. + +get_locked_file_path:: + + Return the path of the file that is locked by the specified + lock_file object. The caller must free the memory. + +commit_lock_file:: + + Take a pointer to the `struct lock_file` initialized with an + earlier call to `hold_lock_file_for_update` or + `hold_lock_file_for_append`, close the file descriptor, and + rename the lockfile to its final destination. Return 0 upon + success. On failure, roll back the lock file and return -1, + with `errno` set to the value from the failing call to + `close(2)` or `rename(2)`. It is a bug to call + `commit_lock_file` for a `lock_file` object that is not + currently locked. + +commit_lock_file_to:: + + Like `commit_lock_file()`, except that it takes an explicit + `path` argument to which the lockfile should be renamed. The + `path` must be on the same filesystem as the lock file. + +rollback_lock_file:: + + Take a pointer to the `struct lock_file` initialized with an + earlier call to `hold_lock_file_for_update` or + `hold_lock_file_for_append`, close the file descriptor and + remove the lockfile. It is a NOOP to call + `rollback_lock_file()` for a `lock_file` object that has + already been committed or rolled back. + +close_lock_file:: + + Take a pointer to the `struct lock_file` initialized with an + earlier call to `hold_lock_file_for_update` or + `hold_lock_file_for_append`. Close the file descriptor (and + the file pointer if it has been opened using + `fdopen_lock_file`). Return 0 upon success. On failure to + `close(2)`, return a negative value and roll back the lock + file. Usually `commit_lock_file`, `commit_lock_file_to`, or + `rollback_lock_file` should eventually be called if + `close_lock_file` succeeds. + +reopen_lock_file:: + + Re-open a lockfile that has been closed (using + `close_lock_file`) but not yet committed or rolled back. This + can be used to implement a sequence of operations like the + following: + + * Lock file. + + * Write new contents to lockfile, then `close_lock_file` to + cause the contents to be written to disk. + + * Pass the name of the lockfile to another program to allow it + (and nobody else) to inspect the contents you wrote, while + still holding the lock yourself. + + * `reopen_lock_file` to reopen the lockfile. Make further + updates to the contents. + + * `commit_lock_file` to make the final version permanent. diff --git a/Documentation/technical/api-merge.txt b/Documentation/technical/api-merge.txt new file mode 100644 index 0000000000..9dc1bed768 --- /dev/null +++ b/Documentation/technical/api-merge.txt @@ -0,0 +1,104 @@ +merge API +========= + +The merge API helps a program to reconcile two competing sets of +improvements to some files (e.g., unregistered changes from the work +tree versus changes involved in switching to a new branch), reporting +conflicts if found. The library called through this API is +responsible for a few things. + + * determining which trees to merge (recursive ancestor consolidation); + + * lining up corresponding files in the trees to be merged (rename + detection, subtree shifting), reporting edge cases like add/add + and rename/rename conflicts to the user; + + * performing a three-way merge of corresponding files, taking + path-specific merge drivers (specified in `.gitattributes`) + into account. + +Data structures +--------------- + +* `mmbuffer_t`, `mmfile_t` + +These store data usable for use by the xdiff backend, for writing and +for reading, respectively. See `xdiff/xdiff.h` for the definitions +and `diff.c` for examples. + +* `struct ll_merge_options` + +This describes the set of options the calling program wants to affect +the operation of a low-level (single file) merge. Some options: + +`virtual_ancestor`:: + Behave as though this were part of a merge between common + ancestors in a recursive merge. + If a helper program is specified by the + `[merge "<driver>"] recursive` configuration, it will + be used (see linkgit:gitattributes[5]). + +`variant`:: + Resolve local conflicts automatically in favor + of one side or the other (as in 'git merge-file' + `--ours`/`--theirs`/`--union`). Can be `0`, + `XDL_MERGE_FAVOR_OURS`, `XDL_MERGE_FAVOR_THEIRS`, or + `XDL_MERGE_FAVOR_UNION`. + +`renormalize`:: + Resmudge and clean the "base", "theirs" and "ours" files + before merging. Use this when the merge is likely to have + overlapped with a change in smudge/clean or end-of-line + normalization rules. + +Low-level (single file) merge +----------------------------- + +`ll_merge`:: + + Perform a three-way single-file merge in core. This is + a thin wrapper around `xdl_merge` that takes the path and + any merge backend specified in `.gitattributes` or + `.git/info/attributes` into account. Returns 0 for a + clean merge. + +Calling sequence: + +* Prepare a `struct ll_merge_options` to record options. + If you have no special requests, skip this and pass `NULL` + as the `opts` parameter to use the default options. + +* Allocate an mmbuffer_t variable for the result. + +* Allocate and fill variables with the file's original content + and two modified versions (using `read_mmfile`, for example). + +* Call `ll_merge()`. + +* Read the merged content from `result_buf.ptr` and `result_buf.size`. + +* Release buffers when finished. A simple + `free(ancestor.ptr); free(ours.ptr); free(theirs.ptr); + free(result_buf.ptr);` will do. + +If the modifications do not merge cleanly, `ll_merge` will return a +nonzero value and `result_buf` will generally include a description of +the conflict bracketed by markers such as the traditional `<<<<<<<` +and `>>>>>>>`. + +The `ancestor_label`, `our_label`, and `their_label` parameters are +used to label the different sides of a conflict if the merge driver +supports this. + +Everything else +--------------- + +Talk about <merge-recursive.h> and merge_file(): + + - merge_trees() to merge with rename detection + - merge_recursive() for ancestor consolidation + - try_merge_command() for other strategies + - conflict format + - merge options + +(Daniel, Miklos, Stephan, JC) diff --git a/Documentation/technical/api-object-access.txt b/Documentation/technical/api-object-access.txt new file mode 100644 index 0000000000..03bb0e950d --- /dev/null +++ b/Documentation/technical/api-object-access.txt @@ -0,0 +1,15 @@ +object access API +================= + +Talk about <sha1_file.c> and <object.h> family, things like + +* read_sha1_file() +* read_object_with_reference() +* has_sha1_file() +* write_sha1_file() +* pretend_sha1_file() +* lookup_{object,commit,tag,blob,tree} +* parse_{object,commit,tag,blob,tree} +* Use of object flags + +(JC, Shawn, Daniel, Dscho, Linus) diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt new file mode 100644 index 0000000000..1f2db31312 --- /dev/null +++ b/Documentation/technical/api-parse-options.txt @@ -0,0 +1,280 @@ +parse-options API +================= + +The parse-options API is used to parse and massage options in Git +and to provide a usage help with consistent look. + +Basics +------ + +The argument vector `argv[]` may usually contain mandatory or optional +'non-option arguments', e.g. a filename or a branch, and 'options'. +Options are optional arguments that start with a dash and +that allow to change the behavior of a command. + +* There are basically three types of options: + 'boolean' options, + options with (mandatory) 'arguments' and + options with 'optional arguments' + (i.e. a boolean option that can be adjusted). + +* There are basically two forms of options: + 'Short options' consist of one dash (`-`) and one alphanumeric + character. + 'Long options' begin with two dashes (`--`) and some + alphanumeric characters. + +* Options are case-sensitive. + Please define 'lower-case long options' only. + +The parse-options API allows: + +* 'stuck' and 'separate form' of options with arguments. + `-oArg` is stuck, `-o Arg` is separate form. + `--option=Arg` is stuck, `--option Arg` is separate form. + +* Long options may be 'abbreviated', as long as the abbreviation + is unambiguous. + +* Short options may be bundled, e.g. `-a -b` can be specified as `-ab`. + +* Boolean long options can be 'negated' (or 'unset') by prepending + `no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely, + options that begin with `no-` can be 'negated' by removing it. + Other long options can be unset (e.g., set string to NULL, set + integer to 0) by prepending `no-`. + +* Options and non-option arguments can clearly be separated using the `--` + option, e.g. `-a -b --option -- --this-is-a-file` indicates that + `--this-is-a-file` must not be processed as an option. + +Steps to parse options +---------------------- + +. `#include "parse-options.h"` + +. define a NULL-terminated + `static const char * const builtin_foo_usage[]` array + containing alternative usage strings + +. define `builtin_foo_options` array as described below + in section 'Data Structure'. + +. in `cmd_foo(int argc, const char **argv, const char *prefix)` + call + + argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags); ++ +`parse_options()` will filter out the processed options of `argv[]` and leave the +non-option arguments in `argv[]`. +`argc` is updated appropriately because of the assignment. ++ +You can also pass NULL instead of a usage array as the fifth parameter of +parse_options(), to avoid displaying a help screen with usage info and +option list. This should only be done if necessary, e.g. to implement +a limited parser for only a subset of the options that needs to be run +before the full parser, which in turn shows the full help message. ++ +Flags are the bitwise-or of: + +`PARSE_OPT_KEEP_DASHDASH`:: + Keep the `--` that usually separates options from + non-option arguments. + +`PARSE_OPT_STOP_AT_NON_OPTION`:: + Usually the whole argument vector is massaged and reordered. + Using this flag, processing is stopped at the first non-option + argument. + +`PARSE_OPT_KEEP_ARGV0`:: + Keep the first argument, which contains the program name. It's + removed from argv[] by default. + +`PARSE_OPT_KEEP_UNKNOWN`:: + Keep unknown arguments instead of erroring out. This doesn't + work for all combinations of arguments as users might expect + it to do. E.g. if the first argument in `--unknown --known` + takes a value (which we can't know), the second one is + mistakenly interpreted as a known option. Similarly, if + `PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in + `--unknown value` will be mistakenly interpreted as a + non-option, not as a value belonging to the unknown option, + the parser early. That's why parse_options() errors out if + both options are set. + +`PARSE_OPT_NO_INTERNAL_HELP`:: + By default, parse_options() handles `-h`, `--help` and + `--help-all` internally, by showing a help screen. This option + turns it off and allows one to add custom handlers for these + options, or to just leave them unknown. + +Data Structure +-------------- + +The main data structure is an array of the `option` struct, +say `static struct option builtin_add_options[]`. +There are some macros to easily define options: + +`OPT__ABBREV(&int_var)`:: + Add `--abbrev[=<n>]`. + +`OPT__COLOR(&int_var, description)`:: + Add `--color[=<when>]` and `--no-color`. + +`OPT__DRY_RUN(&int_var, description)`:: + Add `-n, --dry-run`. + +`OPT__FORCE(&int_var, description)`:: + Add `-f, --force`. + +`OPT__QUIET(&int_var, description)`:: + Add `-q, --quiet`. + +`OPT__VERBOSE(&int_var, description)`:: + Add `-v, --verbose`. + +`OPT_GROUP(description)`:: + Start an option group. `description` is a short string that + describes the group or an empty string. + Start the description with an upper-case letter. + +`OPT_BOOL(short, long, &int_var, description)`:: + Introduce a boolean option. `int_var` is set to one with + `--option` and set to zero with `--no-option`. + +`OPT_COUNTUP(short, long, &int_var, description)`:: + Introduce a count-up option. + `int_var` is incremented on each use of `--option`, and + reset to zero with `--no-option`. + +`OPT_BIT(short, long, &int_var, description, mask)`:: + Introduce a boolean option. + If used, `int_var` is bitwise-ored with `mask`. + +`OPT_NEGBIT(short, long, &int_var, description, mask)`:: + Introduce a boolean option. + If used, `int_var` is bitwise-anded with the inverted `mask`. + +`OPT_SET_INT(short, long, &int_var, description, integer)`:: + Introduce an integer option. + `int_var` is set to `integer` with `--option`, and + reset to zero with `--no-option`. + +`OPT_STRING(short, long, &str_var, arg_str, description)`:: + Introduce an option with string argument. + The string argument is put into `str_var`. + +`OPT_INTEGER(short, long, &int_var, description)`:: + Introduce an option with integer argument. + The integer is put into `int_var`. + +`OPT_DATE(short, long, &int_var, description)`:: + Introduce an option with date argument, see `approxidate()`. + The timestamp is put into `int_var`. + +`OPT_EXPIRY_DATE(short, long, &int_var, description)`:: + Introduce an option with expiry date argument, see `parse_expiry_date()`. + The timestamp is put into `int_var`. + +`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`:: + Introduce an option with argument. + The argument will be fed into the function given by `func_ptr` + and the result will be put into `var`. + See 'Option Callbacks' below for a more elaborate description. + +`OPT_FILENAME(short, long, &var, description)`:: + Introduce an option with a filename argument. + The filename will be prefixed by passing the filename along with + the prefix argument of `parse_options()` to `prefix_filename()`. + +`OPT_ARGUMENT(long, description)`:: + Introduce a long-option argument that will be kept in `argv[]`. + +`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`:: + Recognize numerical options like -123 and feed the integer as + if it was an argument to the function given by `func_ptr`. + The result will be put into `var`. There can be only one such + option definition. It cannot be negated and it takes no + arguments. Short options that happen to be digits take + precedence over it. + +`OPT_COLOR_FLAG(short, long, &int_var, description)`:: + Introduce an option that takes an optional argument that can + have one of three values: "always", "never", or "auto". If the + argument is not given, it defaults to "always". The `--no-` form + works like `--long=never`; it cannot take an argument. If + "always", set `int_var` to 1; if "never", set `int_var` to 0; if + "auto", set `int_var` to 1 if stdout is a tty or a pager, + 0 otherwise. + +`OPT_NOOP_NOARG(short, long)`:: + Introduce an option that has no effect and takes no arguments. + Use it to hide deprecated options that are still to be recognized + and ignored silently. + + +The last element of the array must be `OPT_END()`. + +If not stated otherwise, interpret the arguments as follows: + +* `short` is a character for the short option + (e.g. `'e'` for `-e`, use `0` to omit), + +* `long` is a string for the long option + (e.g. `"example"` for `--example`, use `NULL` to omit), + +* `int_var` is an integer variable, + +* `str_var` is a string variable (`char *`), + +* `arg_str` is the string that is shown as argument + (e.g. `"branch"` will result in `<branch>`). + If set to `NULL`, three dots (`...`) will be displayed. + +* `description` is a short string to describe the effect of the option. + It shall begin with a lower-case letter and a full stop (`.`) shall be + omitted at the end. + +Option Callbacks +---------------- + +The function must be defined in this form: + + int func(const struct option *opt, const char *arg, int unset) + +The callback mechanism is as follows: + +* Inside `func`, the only interesting member of the structure + given by `opt` is the void pointer `opt->value`. + `*opt->value` will be the value that is saved into `var`, if you + use `OPT_CALLBACK()`. + For example, do `*(unsigned long *)opt->value = 42;` to get 42 + into an `unsigned long` variable. + +* Return value `0` indicates success and non-zero return + value will invoke `usage_with_options()` and, thus, die. + +* If the user negates the option, `arg` is `NULL` and `unset` is 1. + +Sophisticated option parsing +---------------------------- + +If you need, for example, option callbacks with optional arguments +or without arguments at all, or if you need other special cases, +that are not handled by the macros above, you need to specify the +members of the `option` structure manually. + +This is not covered in this document, but well documented +in `parse-options.h` itself. + +Examples +-------- + +See `test-parse-options.c` and +`builtin/add.c`, +`builtin/clone.c`, +`builtin/commit.c`, +`builtin/fetch.c`, +`builtin/fsck.c`, +`builtin/rm.c` +for real-world examples. diff --git a/Documentation/technical/api-quote.txt b/Documentation/technical/api-quote.txt new file mode 100644 index 0000000000..e8a1bce94e --- /dev/null +++ b/Documentation/technical/api-quote.txt @@ -0,0 +1,10 @@ +quote API +========= + +Talk about <quote.h>, things like + +* sq_quote and unquote +* c_style quote and unquote +* quoting for foreign languages + +(JC) diff --git a/Documentation/technical/api-ref-iteration.txt b/Documentation/technical/api-ref-iteration.txt new file mode 100644 index 0000000000..37379d8337 --- /dev/null +++ b/Documentation/technical/api-ref-iteration.txt @@ -0,0 +1,81 @@ +ref iteration API +================= + + +Iteration of refs is done by using an iterate function which will call a +callback function for every ref. The callback function has this +signature: + + int handle_one_ref(const char *refname, const struct object_id *oid, + int flags, void *cb_data); + +There are different kinds of iterate functions which all take a +callback of this type. The callback is then called for each found ref +until the callback returns nonzero. The returned value is then also +returned by the iterate function. + +Iteration functions +------------------- + +* `head_ref()` just iterates the head ref. + +* `for_each_ref()` iterates all refs. + +* `for_each_ref_in()` iterates all refs which have a defined prefix and + strips that prefix from the passed variable refname. + +* `for_each_tag_ref()`, `for_each_branch_ref()`, `for_each_remote_ref()`, + `for_each_replace_ref()` iterate refs from the respective area. + +* `for_each_glob_ref()` iterates all refs that match the specified glob + pattern. + +* `for_each_glob_ref_in()` the previous and `for_each_ref_in()` combined. + +* `head_ref_submodule()`, `for_each_ref_submodule()`, + `for_each_ref_in_submodule()`, `for_each_tag_ref_submodule()`, + `for_each_branch_ref_submodule()`, `for_each_remote_ref_submodule()` + do the same as the functions described above but for a specified + submodule. + +* `for_each_rawref()` can be used to learn about broken ref and symref. + +* `for_each_reflog()` iterates each reflog file. + +Submodules +---------- + +If you want to iterate the refs of a submodule you first need to add the +submodules object database. You can do this by a code-snippet like +this: + + const char *path = "path/to/submodule" + if (add_submodule_odb(path)) + die("Error submodule '%s' not populated.", path); + +`add_submodule_odb()` will return zero on success. If you +do not do this you will get an error for each ref that it does not point +to a valid object. + +Note: As a side-effect of this you can not safely assume that all +objects you lookup are available in superproject. All submodule objects +will be available the same way as the superprojects objects. + +Example: +-------- + +---- +static int handle_remote_ref(const char *refname, + const unsigned char *sha1, int flags, void *cb_data) +{ + struct strbuf *output = cb_data; + strbuf_addf(output, "%s\n", refname); + return 0; +} + +... + + struct strbuf output = STRBUF_INIT; + for_each_remote_ref(handle_remote_ref, &output); + printf("%s", output.buf); +---- diff --git a/Documentation/technical/api-remote.txt b/Documentation/technical/api-remote.txt new file mode 100644 index 0000000000..2cfdd224a8 --- /dev/null +++ b/Documentation/technical/api-remote.txt @@ -0,0 +1,123 @@ +Remotes configuration API +========================= + +The API in remote.h gives access to the configuration related to +remotes. It handles all three configuration mechanisms historically +and currently used by Git, and presents the information in a uniform +fashion. Note that the code also handles plain URLs without any +configuration, giving them just the default information. + +struct remote +------------- + +`name`:: + + The user's nickname for the remote + +`url`:: + + An array of all of the url_nr URLs configured for the remote + +`pushurl`:: + + An array of all of the pushurl_nr push URLs configured for the remote + +`push`:: + + An array of refspecs configured for pushing, with + push_refspec being the literal strings, and push_refspec_nr + being the quantity. + +`fetch`:: + + An array of refspecs configured for fetching, with + fetch_refspec being the literal strings, and fetch_refspec_nr + being the quantity. + +`fetch_tags`:: + + The setting for whether to fetch tags (as a separate rule from + the configured refspecs); -1 means never to fetch tags, 0 + means to auto-follow tags based on the default heuristic, 1 + means to always auto-follow tags, and 2 means to fetch all + tags. + +`receivepack`, `uploadpack`:: + + The configured helper programs to run on the remote side, for + Git-native protocols. + +`http_proxy`:: + + The proxy to use for curl (http, https, ftp, etc.) URLs. + +struct remotes can be found by name with remote_get(), and iterated +through with for_each_remote(). remote_get(NULL) will return the +default remote, given the current branch and configuration. + +struct refspec +-------------- + +A struct refspec holds the parsed interpretation of a refspec. If it +will force updates (starts with a '+'), force is true. If it is a +pattern (sides end with '*') pattern is true. src and dest are the +two sides (including '*' characters if present); if there is only one +side, it is src, and dst is NULL; if sides exist but are empty (i.e., +the refspec either starts or ends with ':'), the corresponding side is +"". + +An array of strings can be parsed into an array of struct refspecs +using parse_fetch_refspec() or parse_push_refspec(). + +remote_find_tracking(), given a remote and a struct refspec with +either src or dst filled out, will fill out the other such that the +result is in the "fetch" specification for the remote (note that this +evaluates patterns and returns a single result). + +struct branch +------------- + +Note that this may end up moving to branch.h + +struct branch holds the configuration for a branch. It can be looked +up with branch_get(name) for "refs/heads/{name}", or with +branch_get(NULL) for HEAD. + +It contains: + +`name`:: + + The short name of the branch. + +`refname`:: + + The full path for the branch ref. + +`remote_name`:: + + The name of the remote listed in the configuration. + +`merge_name`:: + + An array of the "merge" lines in the configuration. + +`merge`:: + + An array of the struct refspecs used for the merge lines. That + is, merge[i]->dst is a local tracking ref which should be + merged into this branch by default. + +`merge_nr`:: + + The number of merge configurations + +branch_has_merge_config() returns true if the given branch has merge +configuration given. + +Other stuff +----------- + +There is other stuff in remote.h that is related, in general, to the +process of interacting with remotes. + +(Daniel Barkalow) diff --git a/Documentation/technical/api-revision-walking.txt b/Documentation/technical/api-revision-walking.txt new file mode 100644 index 0000000000..55b878ade8 --- /dev/null +++ b/Documentation/technical/api-revision-walking.txt @@ -0,0 +1,72 @@ +revision walking API +==================== + +The revision walking API offers functions to build a list of revisions +and then iterate over that list. + +Calling sequence +---------------- + +The walking API has a given calling sequence: first you need to +initialize a rev_info structure, then add revisions to control what kind +of revision list do you want to get, finally you can iterate over the +revision list. + +Functions +--------- + +`init_revisions`:: + + Initialize a rev_info structure with default values. The second + parameter may be NULL or can be prefix path, and then the `.prefix` + variable will be set to it. This is typically the first function you + want to call when you want to deal with a revision list. After calling + this function, you are free to customize options, like set + `.ignore_merges` to 0 if you don't want to ignore merges, and so on. See + `revision.h` for a complete list of available options. + +`add_pending_object`:: + + This function can be used if you want to add commit objects as revision + information. You can use the `UNINTERESTING` object flag to indicate if + you want to include or exclude the given commit (and commits reachable + from the given commit) from the revision list. ++ +NOTE: If you have the commits as a string list then you probably want to +use setup_revisions(), instead of parsing each string and using this +function. + +`setup_revisions`:: + + Parse revision information, filling in the `rev_info` structure, and + removing the used arguments from the argument list. Returns the number + of arguments left that weren't recognized, which are also moved to the + head of the argument list. The last parameter is used in case no + parameter given by the first two arguments. + +`prepare_revision_walk`:: + + Prepares the rev_info structure for a walk. You should check if it + returns any error (non-zero return code) and if it does not, you can + start using get_revision() to do the iteration. + +`get_revision`:: + + Takes a pointer to a `rev_info` structure and iterates over it, + returning a `struct commit *` each time you call it. The end of the + revision list is indicated by returning a NULL pointer. + +`reset_revision_walk`:: + + Reset the flags used by the revision walking api. You can use + this to do multiple sequential revision walks. + +Data structures +--------------- + +Talk about <revision.h>, things like: + +* two diff_options, one for path limiting, another for output; +* remaining functions; + +(Linus, JC, Dscho) diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt new file mode 100644 index 0000000000..a9fdb45b93 --- /dev/null +++ b/Documentation/technical/api-run-command.txt @@ -0,0 +1,257 @@ +run-command API +=============== + +The run-command API offers a versatile tool to run sub-processes with +redirected input and output as well as with a modified environment +and an alternate current directory. + +A similar API offers the capability to run a function asynchronously, +which is primarily used to capture the output that the function +produces in the caller in order to process it. + + +Functions +--------- + +`child_process_init`:: + + Initialize a struct child_process variable. + +`start_command`:: + + Start a sub-process. Takes a pointer to a `struct child_process` + that specifies the details and returns pipe FDs (if requested). + See below for details. + +`finish_command`:: + + Wait for the completion of a sub-process that was started with + start_command(). + +`run_command`:: + + A convenience function that encapsulates a sequence of + start_command() followed by finish_command(). Takes a pointer + to a `struct child_process` that specifies the details. + +`run_command_v_opt`, `run_command_v_opt_cd_env`:: + + Convenience functions that encapsulate a sequence of + start_command() followed by finish_command(). The argument argv + specifies the program and its arguments. The argument opt is zero + or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`, + `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE` + that correspond to the members .no_stdin, .git_cmd, + .stdout_to_stderr, .silent_exec_failure of `struct child_process`. + The argument dir corresponds the member .dir. The argument env + corresponds to the member .env. + +The functions above do the following: + +. If a system call failed, errno is set and -1 is returned. A diagnostic + is printed. + +. If the program was not found, then -1 is returned and errno is set to + ENOENT; a diagnostic is printed only if .silent_exec_failure is 0. + +. Otherwise, the program is run. If it terminates regularly, its exit + code is returned. No diagnostic is printed, even if the exit code is + non-zero. + +. If the program terminated due to a signal, then the return value is the + signal number + 128, ie. the same value that a POSIX shell's $? would + report. A diagnostic is printed. + + +`start_async`:: + + Run a function asynchronously. Takes a pointer to a `struct + async` that specifies the details and returns a set of pipe FDs + for communication with the function. See below for details. + +`finish_async`:: + + Wait for the completion of an asynchronous function that was + started with start_async(). + +`run_hook`:: + + Run a hook. + The first argument is a pathname to an index file, or NULL + if the hook uses the default index file or no index is needed. + The second argument is the name of the hook. + The further arguments correspond to the hook arguments. + The last argument has to be NULL to terminate the arguments list. + If the hook does not exist or is not executable, the return + value will be zero. + If it is executable, the hook will be executed and the exit + status of the hook is returned. + On execution, .stdout_to_stderr and .no_stdin will be set. + (See below.) + + +Data structures +--------------- + +* `struct child_process` + +This describes the arguments, redirections, and environment of a +command to run in a sub-process. + +The caller: + +1. allocates and clears (using child_process_init() or + CHILD_PROCESS_INIT) a struct child_process variable; +2. initializes the members; +3. calls start_command(); +4. processes the data; +5. closes file descriptors (if necessary; see below); +6. calls finish_command(). + +The .argv member is set up as an array of string pointers (NULL +terminated), of which .argv[0] is the program name to run (usually +without a path). If the command to run is a git command, set argv[0] to +the command name without the 'git-' prefix and set .git_cmd = 1. + +Note that the ownership of the memory pointed to by .argv stays with the +caller, but it should survive until `finish_command` completes. If the +.argv member is NULL, `start_command` will point it at the .args +`argv_array` (so you may use one or the other, but you must use exactly +one). The memory in .args will be cleaned up automatically during +`finish_command` (or during `start_command` when it is unsuccessful). + +The members .in, .out, .err are used to redirect stdin, stdout, +stderr as follows: + +. Specify 0 to request no special redirection. No new file descriptor + is allocated. The child process simply inherits the channel from the + parent. + +. Specify -1 to have a pipe allocated; start_command() replaces -1 + by the pipe FD in the following way: + + .in: Returns the writable pipe end into which the caller writes; + the readable end of the pipe becomes the child's stdin. + + .out, .err: Returns the readable pipe end from which the caller + reads; the writable end of the pipe end becomes child's + stdout/stderr. + + The caller of start_command() must close the so returned FDs + after it has completed reading from/writing to it! + +. Specify a file descriptor > 0 to be used by the child: + + .in: The FD must be readable; it becomes child's stdin. + .out: The FD must be writable; it becomes child's stdout. + .err: The FD must be writable; it becomes child's stderr. + + The specified FD is closed by start_command(), even if it fails to + run the sub-process! + +. Special forms of redirection are available by setting these members + to 1: + + .no_stdin, .no_stdout, .no_stderr: The respective channel is + redirected to /dev/null. + + .stdout_to_stderr: stdout of the child is redirected to its + stderr. This happens after stderr is itself redirected. + So stdout will follow stderr to wherever it is + redirected. + +To modify the environment of the sub-process, specify an array of +string pointers (NULL terminated) in .env: + +. If the string is of the form "VAR=value", i.e. it contains '=' + the variable is added to the child process's environment. + +. If the string does not contain '=', it names an environment + variable that will be removed from the child process's environment. + +If the .env member is NULL, `start_command` will point it at the +.env_array `argv_array` (so you may use one or the other, but not both). +The memory in .env_array will be cleaned up automatically during +`finish_command` (or during `start_command` when it is unsuccessful). + +To specify a new initial working directory for the sub-process, +specify it in the .dir member. + +If the program cannot be found, the functions return -1 and set +errno to ENOENT. Normally, an error message is printed, but if +.silent_exec_failure is set to 1, no message is printed for this +special error condition. + + +* `struct async` + +This describes a function to run asynchronously, whose purpose is +to produce output that the caller reads. + +The caller: + +1. allocates and clears (memset(&asy, 0, sizeof(asy));) a + struct async variable; +2. initializes .proc and .data; +3. calls start_async(); +4. processes communicates with proc through .in and .out; +5. closes .in and .out; +6. calls finish_async(). + +The members .in, .out are used to provide a set of fd's for +communication between the caller and the callee as follows: + +. Specify 0 to have no file descriptor passed. The callee will + receive -1 in the corresponding argument. + +. Specify < 0 to have a pipe allocated; start_async() replaces + with the pipe FD in the following way: + + .in: Returns the writable pipe end into which the caller + writes; the readable end of the pipe becomes the function's + in argument. + + .out: Returns the readable pipe end from which the caller + reads; the writable end of the pipe becomes the function's + out argument. + + The caller of start_async() must close the returned FDs after it + has completed reading from/writing from them. + +. Specify a file descriptor > 0 to be used by the function: + + .in: The FD must be readable; it becomes the function's in. + .out: The FD must be writable; it becomes the function's out. + + The specified FD is closed by start_async(), even if it fails to + run the function. + +The function pointer in .proc has the following signature: + + int proc(int in, int out, void *data); + +. in, out specifies a set of file descriptors to which the function + must read/write the data that it needs/produces. The function + *must* close these descriptors before it returns. A descriptor + may be -1 if the caller did not configure a descriptor for that + direction. + +. data is the value that the caller has specified in the .data member + of struct async. + +. The return value of the function is 0 on success and non-zero + on failure. If the function indicates failure, finish_async() will + report failure as well. + + +There are serious restrictions on what the asynchronous function can do +because this facility is implemented by a thread in the same address +space on most platforms (when pthreads is available), but by a pipe to +a forked process otherwise: + +. It cannot change the program's state (global variables, environment, + etc.) in a way that the caller notices; in other words, .in and .out + are the only communication channels to the caller. + +. It must not change the program's state that the caller of the + facility also uses. diff --git a/Documentation/technical/api-setup.txt b/Documentation/technical/api-setup.txt new file mode 100644 index 0000000000..540e455689 --- /dev/null +++ b/Documentation/technical/api-setup.txt @@ -0,0 +1,49 @@ +setup API +========= + +Talk about + +* setup_git_directory() +* setup_git_directory_gently() +* is_inside_git_dir() +* is_inside_work_tree() +* setup_work_tree() + +(Dscho) + +Pathspec +-------- + +See glossary-context.txt for the syntax of pathspec. In memory, a +pathspec set is represented by "struct pathspec" and is prepared by +parse_pathspec(). This function takes several arguments: + +- magic_mask specifies what features that are NOT supported by the + following code. If a user attempts to use such a feature, + parse_pathspec() can reject it early. + +- flags specifies other things that the caller wants parse_pathspec to + perform. + +- prefix and args come from cmd_* functions + +get_pathspec() is obsolete and should never be used in new code. + +parse_pathspec() helps catch unsupported features and reject them +politely. At a lower level, different pathspec-related functions may +not support the same set of features. Such pathspec-sensitive +functions are guarded with GUARD_PATHSPEC(), which will die in an +unfriendly way when an unsupported feature is requested. + +The command designers are supposed to make sure that GUARD_PATHSPEC() +never dies. They have to make sure all unsupported features are caught +by parse_pathspec(), not by GUARD_PATHSPEC. grepping GUARD_PATHSPEC() +should give the designers all pathspec-sensitive codepaths and what +features they support. + +A similar process is applied when a new pathspec magic is added. The +designer lifts the GUARD_PATHSPEC restriction in the functions that +support the new magic. At the same time (s)he has to make sure this +new feature will be caught at parse_pathspec() in commands that cannot +handle the new magic in some cases. grepping parse_pathspec() should +help. diff --git a/Documentation/technical/api-sha1-array.txt b/Documentation/technical/api-sha1-array.txt new file mode 100644 index 0000000000..3e75497a37 --- /dev/null +++ b/Documentation/technical/api-sha1-array.txt @@ -0,0 +1,76 @@ +sha1-array API +============== + +The sha1-array API provides storage and manipulation of sets of SHA-1 +identifiers. The emphasis is on storage and processing efficiency, +making them suitable for large lists. Note that the ordering of items is +not preserved over some operations. + +Data Structures +--------------- + +`struct sha1_array`:: + + A single array of SHA-1 hashes. This should be initialized by + assignment from `SHA1_ARRAY_INIT`. The `sha1` member contains + the actual data. The `nr` member contains the number of items in + the set. The `alloc` and `sorted` members are used internally, + and should not be needed by API callers. + +Functions +--------- + +`sha1_array_append`:: + Add an item to the set. The sha1 will be placed at the end of + the array (but note that some operations below may lose this + ordering). + +`sha1_array_lookup`:: + Perform a binary search of the array for a specific sha1. + If found, returns the offset (in number of elements) of the + sha1. If not found, returns a negative integer. If the array is + not sorted, this function has the side effect of sorting it. + +`sha1_array_clear`:: + Free all memory associated with the array and return it to the + initial, empty state. + +`sha1_array_for_each_unique`:: + Efficiently iterate over each unique element of the list, + executing the callback function for each one. If the array is + not sorted, this function has the side effect of sorting it. + +Examples +-------- + +----------------------------------------- +void print_callback(const unsigned char sha1[20], + void *data) +{ + printf("%s\n", sha1_to_hex(sha1)); +} + +void some_func(void) +{ + struct sha1_array hashes = SHA1_ARRAY_INIT; + unsigned char sha1[20]; + + /* Read objects into our set */ + while (read_object_from_stdin(sha1)) + sha1_array_append(&hashes, sha1); + + /* Check if some objects are in our set */ + while (read_object_from_stdin(sha1)) { + if (sha1_array_lookup(&hashes, sha1) >= 0) + printf("it's in there!\n"); + + /* + * Print the unique set of objects. We could also have + * avoided adding duplicate objects in the first place, + * but we would end up re-sorting the array repeatedly. + * Instead, this will sort once and then skip duplicates + * in linear time. + */ + sha1_array_for_each_unique(&hashes, print_callback, NULL); +} +----------------------------------------- diff --git a/Documentation/technical/api-sigchain.txt b/Documentation/technical/api-sigchain.txt new file mode 100644 index 0000000000..9e1189ef01 --- /dev/null +++ b/Documentation/technical/api-sigchain.txt @@ -0,0 +1,41 @@ +sigchain API +============ + +Code often wants to set a signal handler to clean up temporary files or +other work-in-progress when we die unexpectedly. For multiple pieces of +code to do this without conflicting, each piece of code must remember +the old value of the handler and restore it either when: + + 1. The work-in-progress is finished, and the handler is no longer + necessary. The handler should revert to the original behavior + (either another handler, SIG_DFL, or SIG_IGN). + + 2. The signal is received. We should then do our cleanup, then chain + to the next handler (or die if it is SIG_DFL). + +Sigchain is a tiny library for keeping a stack of handlers. Your handler +and installation code should look something like: + +------------------------------------------ + void clean_foo_on_signal(int sig) + { + clean_foo(); + sigchain_pop(sig); + raise(sig); + } + + void other_func() + { + sigchain_push_common(clean_foo_on_signal); + mess_up_foo(); + clean_foo(); + } +------------------------------------------ + +Handlers are given the typedef of sigchain_fun. This is the same type +that is given to signal() or sigaction(). It is perfectly reasonable to +push SIG_DFL or SIG_IGN onto the stack. + +You can sigchain_push and sigchain_pop individual signals. For +convenience, sigchain_push_common will push the handler onto the stack +for many common signals. diff --git a/Documentation/technical/api-string-list.txt b/Documentation/technical/api-string-list.txt new file mode 100644 index 0000000000..c08402b12e --- /dev/null +++ b/Documentation/technical/api-string-list.txt @@ -0,0 +1,209 @@ +string-list API +=============== + +The string_list API offers a data structure and functions to handle +sorted and unsorted string lists. A "sorted" list is one whose +entries are sorted by string value in `strcmp()` order. + +The 'string_list' struct used to be called 'path_list', but was renamed +because it is not specific to paths. + +The caller: + +. Allocates and clears a `struct string_list` variable. + +. Initializes the members. You might want to set the flag `strdup_strings` + if the strings should be strdup()ed. For example, this is necessary + when you add something like git_path("..."), since that function returns + a static buffer that will change with the next call to git_path(). ++ +If you need something advanced, you can manually malloc() the `items` +member (you need this if you add things later) and you should set the +`nr` and `alloc` members in that case, too. + +. Adds new items to the list, using `string_list_append`, + `string_list_append_nodup`, `string_list_insert`, + `string_list_split`, and/or `string_list_split_in_place`. + +. Can check if a string is in the list using `string_list_has_string` or + `unsorted_string_list_has_string` and get it from the list using + `string_list_lookup` for sorted lists. + +. Can sort an unsorted list using `string_list_sort`. + +. Can remove duplicate items from a sorted list using + `string_list_remove_duplicates`. + +. Can remove individual items of an unsorted list using + `unsorted_string_list_delete_item`. + +. Can remove items not matching a criterion from a sorted or unsorted + list using `filter_string_list`, or remove empty strings using + `string_list_remove_empty_items`. + +. Finally it should free the list using `string_list_clear`. + +Example: + +---- +struct string_list list = STRING_LIST_INIT_NODUP; +int i; + +string_list_append(&list, "foo"); +string_list_append(&list, "bar"); +for (i = 0; i < list.nr; i++) + printf("%s\n", list.items[i].string) +---- + +NOTE: It is more efficient to build an unsorted list and sort it +afterwards, instead of building a sorted list (`O(n log n)` instead of +`O(n^2)`). ++ +However, if you use the list to check if a certain string was added +already, you should not do that (using unsorted_string_list_has_string()), +because the complexity would be quadratic again (but with a worse factor). + +Functions +--------- + +* General ones (works with sorted and unsorted lists as well) + +`string_list_init`:: + + Initialize the members of the string_list, set `strdup_strings` + member according to the value of the second parameter. + +`filter_string_list`:: + + Apply a function to each item in a list, retaining only the + items for which the function returns true. If free_util is + true, call free() on the util members of any items that have + to be deleted. Preserve the order of the items that are + retained. + +`string_list_remove_empty_items`:: + + Remove any empty strings from the list. If free_util is true, + call free() on the util members of any items that have to be + deleted. Preserve the order of the items that are retained. + +`print_string_list`:: + + Dump a string_list to stdout, useful mainly for debugging purposes. It + can take an optional header argument and it writes out the + string-pointer pairs of the string_list, each one in its own line. + +`string_list_clear`:: + + Free a string_list. The `string` pointer of the items will be freed in + case the `strdup_strings` member of the string_list is set. The second + parameter controls if the `util` pointer of the items should be freed + or not. + +* Functions for sorted lists only + +`string_list_has_string`:: + + Determine if the string_list has a given string or not. + +`string_list_insert`:: + + Insert a new element to the string_list. The returned pointer can be + handy if you want to write something to the `util` pointer of the + string_list_item containing the just added string. If the given + string already exists the insertion will be skipped and the + pointer to the existing item returned. ++ +Since this function uses xrealloc() (which die()s if it fails) if the +list needs to grow, it is safe not to check the pointer. I.e. you may +write `string_list_insert(...)->util = ...;`. + +`string_list_lookup`:: + + Look up a given string in the string_list, returning the containing + string_list_item. If the string is not found, NULL is returned. + +`string_list_remove_duplicates`:: + + Remove all but the first of consecutive entries that have the + same string value. If free_util is true, call free() on the + util members of any items that have to be deleted. + +* Functions for unsorted lists only + +`string_list_append`:: + + Append a new string to the end of the string_list. If + `strdup_string` is set, then the string argument is copied; + otherwise the new `string_list_entry` refers to the input + string. + +`string_list_append_nodup`:: + + Append a new string to the end of the string_list. The new + `string_list_entry` always refers to the input string, even if + `strdup_string` is set. This function can be used to hand + ownership of a malloc()ed string to a `string_list` that has + `strdup_string` set. + +`string_list_sort`:: + + Sort the list's entries by string value in `strcmp()` order. + +`unsorted_string_list_has_string`:: + + It's like `string_list_has_string()` but for unsorted lists. + +`unsorted_string_list_lookup`:: + + It's like `string_list_lookup()` but for unsorted lists. ++ +The above two functions need to look through all items, as opposed to their +counterpart for sorted lists, which performs a binary search. + +`unsorted_string_list_delete_item`:: + + Remove an item from a string_list. The `string` pointer of the items + will be freed in case the `strdup_strings` member of the string_list + is set. The third parameter controls if the `util` pointer of the + items should be freed or not. + +`string_list_split`:: +`string_list_split_in_place`:: + + Split a string into substrings on a delimiter character and + append the substrings to a `string_list`. If `maxsplit` is + non-negative, then split at most `maxsplit` times. Return the + number of substrings appended to the list. ++ +`string_list_split` requires a `string_list` that has `strdup_strings` +set to true; it leaves the input string untouched and makes copies of +the substrings in newly-allocated memory. +`string_list_split_in_place` requires a `string_list` that has +`strdup_strings` set to false; it splits the input string in place, +overwriting the delimiter characters with NULs and creating new +string_list_items that point into the original string (the original +string must therefore not be modified or freed while the `string_list` +is in use). + + +Data structures +--------------- + +* `struct string_list_item` + +Represents an item of the list. The `string` member is a pointer to the +string, and you may use the `util` member for any purpose, if you want. + +* `struct string_list` + +Represents the list itself. + +. The array of items are available via the `items` member. +. The `nr` member contains the number of items stored in the list. +. The `alloc` member is used to avoid reallocating at every insertion. + You should not tamper with it. +. Setting the `strdup_strings` member to 1 will strdup() the strings + before adding them, see above. +. The `compare_strings_fn` member is used to specify a custom compare + function, otherwise `strcmp()` is used as the default function. diff --git a/Documentation/technical/api-trace.txt b/Documentation/technical/api-trace.txt new file mode 100644 index 0000000000..097a651d96 --- /dev/null +++ b/Documentation/technical/api-trace.txt @@ -0,0 +1,97 @@ +trace API +========= + +The trace API can be used to print debug messages to stderr or a file. Trace +code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment +variables. + +The trace implementation automatically adds `timestamp file:line ... \n` to +all trace messages. E.g.: + +------------ +23:59:59.123456 git.c:312 trace: built-in: git 'foo' +00:00:00.000001 builtin/foo.c:99 foo: some message +------------ + +Data Structures +--------------- + +`struct trace_key`:: + + Defines a trace key (or category). The default (for API functions that + don't take a key) is `GIT_TRACE`. ++ +E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`: ++ +------------ +static struct trace_key trace_foo = TRACE_KEY_INIT(FOO); + +static void trace_print_foo(const char *message) +{ + trace_print_key(&trace_foo, message); +} +------------ ++ +Note: don't use `const` as the trace implementation stores internal state in +the `trace_key` structure. + +Functions +--------- + +`int trace_want(struct trace_key *key)`:: + + Checks whether the trace key is enabled. Used to prevent expensive + string formatting before calling one of the printing APIs. + +`void trace_disable(struct trace_key *key)`:: + + Disables tracing for the specified key, even if the environment + variable was set. + +`void trace_printf(const char *format, ...)`:: +`void trace_printf_key(struct trace_key *key, const char *format, ...)`:: + + Prints a formatted message, similar to printf. + +`void trace_argv_printf(const char **argv, const char *format, ...)``:: + + Prints a formatted message, followed by a quoted list of arguments. + +`void trace_strbuf(struct trace_key *key, const struct strbuf *data)`:: + + Prints the strbuf, without additional formatting (i.e. doesn't + choke on `%` or even `\0`). + +`uint64_t getnanotime(void)`:: + + Returns nanoseconds since the epoch (01/01/1970), typically used + for performance measurements. ++ +Currently there are high precision timer implementations for Linux (using +`clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`). +Other platforms use `gettimeofday` as time source. + +`void trace_performance(uint64_t nanos, const char *format, ...)`:: +`void trace_performance_since(uint64_t start, const char *format, ...)`:: + + Prints the elapsed time (in nanoseconds), or elapsed time since + `start`, followed by a formatted message. Enabled via environment + variable `GIT_TRACE_PERFORMANCE`. Used for manual profiling, e.g.: ++ +------------ +uint64_t start = getnanotime(); +/* code section to measure */ +trace_performance_since(start, "foobar"); +------------ ++ +------------ +uint64_t t = 0; +for (;;) { + /* ignore */ + t -= getnanotime(); + /* code section to measure */ + t += getnanotime(); + /* ignore */ +} +trace_performance(t, "frotz"); +------------ diff --git a/Documentation/technical/api-tree-walking.txt b/Documentation/technical/api-tree-walking.txt new file mode 100644 index 0000000000..14af37c3f1 --- /dev/null +++ b/Documentation/technical/api-tree-walking.txt @@ -0,0 +1,147 @@ +tree walking API +================ + +The tree walking API is used to traverse and inspect trees. + +Data Structures +--------------- + +`struct name_entry`:: + + An entry in a tree. Each entry has a sha1 identifier, pathname, and + mode. + +`struct tree_desc`:: + + A semi-opaque data structure used to maintain the current state of the + walk. ++ +* `buffer` is a pointer into the memory representation of the tree. It always +points at the current entry being visited. + +* `size` counts the number of bytes left in the `buffer`. + +* `entry` points to the current entry being visited. + +`struct traverse_info`:: + + A structure used to maintain the state of a traversal. ++ +* `prev` points to the traverse_info which was used to descend into the +current tree. If this is the top-level tree `prev` will point to +a dummy traverse_info. + +* `name` is the entry for the current tree (if the tree is a subtree). + +* `pathlen` is the length of the full path for the current tree. + +* `conflicts` can be used by callbacks to maintain directory-file conflicts. + +* `fn` is a callback called for each entry in the tree. See Traversing for more +information. + +* `data` can be anything the `fn` callback would want to use. + +* `show_all_errors` tells whether to stop at the first error or not. + +Initializing +------------ + +`init_tree_desc`:: + + Initialize a `tree_desc` and decode its first entry. The buffer and + size parameters are assumed to be the same as the buffer and size + members of `struct tree`. + +`fill_tree_descriptor`:: + + Initialize a `tree_desc` and decode its first entry given the sha1 of + a tree. Returns the `buffer` member if the sha1 is a valid tree + identifier and NULL otherwise. + +`setup_traverse_info`:: + + Initialize a `traverse_info` given the pathname of the tree to start + traversing from. The `base` argument is assumed to be the `path` + member of the `name_entry` being recursed into unless the tree is a + top-level tree in which case the empty string ("") is used. + +Walking +------- + +`tree_entry`:: + + Visit the next entry in a tree. Returns 1 when there are more entries + left to visit and 0 when all entries have been visited. This is + commonly used in the test of a while loop. + +`tree_entry_len`:: + + Calculate the length of a tree entry's pathname. This utilizes the + memory structure of a tree entry to avoid the overhead of using a + generic strlen(). + +`update_tree_entry`:: + + Walk to the next entry in a tree. This is commonly used in conjunction + with `tree_entry_extract` to inspect the current entry. + +`tree_entry_extract`:: + + Decode the entry currently being visited (the one pointed to by + `tree_desc's` `entry` member) and return the sha1 of the entry. The + `pathp` and `modep` arguments are set to the entry's pathname and mode + respectively. + +`get_tree_entry`:: + + Find an entry in a tree given a pathname and the sha1 of a tree to + search. Returns 0 if the entry is found and -1 otherwise. The third + and fourth parameters are set to the entry's sha1 and mode + respectively. + +Traversing +---------- + +`traverse_trees`:: + + Traverse `n` number of trees in parallel. The `fn` callback member of + `traverse_info` is called once for each tree entry. + +`traverse_callback_t`:: + The arguments passed to the traverse callback are as follows: ++ +* `n` counts the number of trees being traversed. + +* `mask` has its nth bit set if something exists in the nth entry. + +* `dirmask` has its nth bit set if the nth tree's entry is a directory. + +* `entry` is an array of size `n` where the nth entry is from the nth tree. + +* `info` maintains the state of the traversal. + ++ +Returning a negative value will terminate the traversal. Otherwise the +return value is treated as an update mask. If the nth bit is set the nth tree +will be updated and if the bit is not set the nth tree entry will be the +same in the next callback invocation. + +`make_traverse_path`:: + + Generate the full pathname of a tree entry based from the root of the + traversal. For example, if the traversal has recursed into another + tree named "bar" the pathname of an entry "baz" in the "bar" + tree would be "bar/baz". + +`traverse_path_len`:: + + Calculate the length of a pathname returned by `make_traverse_path`. + This utilizes the memory structure of a tree entry to avoid the + overhead of using a generic strlen(). + +Authors +------- + +Written by Junio C Hamano <gitster@pobox.com> and Linus Torvalds +<torvalds@linux-foundation.org> diff --git a/Documentation/technical/api-xdiff-interface.txt b/Documentation/technical/api-xdiff-interface.txt new file mode 100644 index 0000000000..6296ecad1d --- /dev/null +++ b/Documentation/technical/api-xdiff-interface.txt @@ -0,0 +1,7 @@ +xdiff interface API +=================== + +Talk about our calling convention to xdiff library, including +xdiff_emit_consume_fn. + +(Dscho, JC) diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt new file mode 100644 index 0000000000..f8c18a0f7a --- /dev/null +++ b/Documentation/technical/bitmap-format.txt @@ -0,0 +1,164 @@ +GIT bitmap v1 format +==================== + + - A header appears at the beginning: + + 4-byte signature: {'B', 'I', 'T', 'M'} + + 2-byte version number (network byte order) + The current implementation only supports version 1 + of the bitmap index (the same one as JGit). + + 2-byte flags (network byte order) + + The following flags are supported: + + - BITMAP_OPT_FULL_DAG (0x1) REQUIRED + This flag must always be present. It implies that the bitmap + index has been generated for a packfile with full closure + (i.e. where every single object in the packfile can find + its parent links inside the same packfile). This is a + requirement for the bitmap index format, also present in JGit, + that greatly reduces the complexity of the implementation. + + - BITMAP_OPT_HASH_CACHE (0x4) + If present, the end of the bitmap file contains + `N` 32-bit name-hash values, one per object in the + pack. The format and meaning of the name-hash is + described below. + + 4-byte entry count (network byte order) + + The total count of entries (bitmapped commits) in this bitmap index. + + 20-byte checksum + + The SHA1 checksum of the pack this bitmap index belongs to. + + - 4 EWAH bitmaps that act as type indexes + + Type indexes are serialized after the hash cache in the shape + of four EWAH bitmaps stored consecutively (see Appendix A for + the serialization format of an EWAH bitmap). + + There is a bitmap for each Git object type, stored in the following + order: + + - Commits + - Trees + - Blobs + - Tags + + In each bitmap, the `n`th bit is set to true if the `n`th object + in the packfile is of that type. + + The obvious consequence is that the OR of all 4 bitmaps will result + in a full set (all bits set), and the AND of all 4 bitmaps will + result in an empty bitmap (no bits set). + + - N entries with compressed bitmaps, one for each indexed commit + + Where `N` is the total amount of entries in this bitmap index. + Each entry contains the following: + + - 4-byte object position (network byte order) + The position **in the index for the packfile** where the + bitmap for this commit is found. + + - 1-byte XOR-offset + The xor offset used to compress this bitmap. For an entry + in position `x`, a XOR offset of `y` means that the actual + bitmap representing this commit is composed by XORing the + bitmap for this entry with the bitmap in entry `x-y` (i.e. + the bitmap `y` entries before this one). + + Note that this compression can be recursive. In order to + XOR this entry with a previous one, the previous entry needs + to be decompressed first, and so on. + + The hard-limit for this offset is 160 (an entry can only be + xor'ed against one of the 160 entries preceding it). This + number is always positive, and hence entries are always xor'ed + with **previous** bitmaps, not bitmaps that will come afterwards + in the index. + + - 1-byte flags for this bitmap + At the moment the only available flag is `0x1`, which hints + that this bitmap can be re-used when rebuilding bitmap indexes + for the repository. + + - The compressed bitmap itself, see Appendix A. + +== Appendix A: Serialization format for an EWAH bitmap + +Ewah bitmaps are serialized in the same protocol as the JAVAEWAH +library, making them backwards compatible with the JGit +implementation: + + - 4-byte number of bits of the resulting UNCOMPRESSED bitmap + + - 4-byte number of words of the COMPRESSED bitmap, when stored + + - N x 8-byte words, as specified by the previous field + + This is the actual content of the compressed bitmap. + + - 4-byte position of the current RLW for the compressed + bitmap + +All words are stored in network byte order for their corresponding +sizes. + +The compressed bitmap is stored in a form of run-length encoding, as +follows. It consists of a concatenation of an arbitrary number of +chunks. Each chunk consists of one or more 64-bit words + + H L_1 L_2 L_3 .... L_M + +H is called RLW (run length word). It consists of (from lower to higher +order bits): + + - 1 bit: the repeated bit B + + - 32 bits: repetition count K (unsigned) + + - 31 bits: literal word count M (unsigned) + +The bitstream represented by the above chunk is then: + + - K repetitions of B + + - The bits stored in `L_1` through `L_M`. Within a word, bits at + lower order come earlier in the stream than those at higher + order. + +The next word after `L_M` (if any) must again be a RLW, for the next +chunk. For efficient appending to the bitstream, the EWAH stores a +pointer to the last RLW in the stream. + + +== Appendix B: Optional Bitmap Sections + +These sections may or may not be present in the `.bitmap` file; their +presence is indicated by the header flags section described above. + +Name-hash cache +--------------- + +If the BITMAP_OPT_HASH_CACHE flag is set, the end of the bitmap contains +a cache of 32-bit values, one per object in the pack. The value at +position `i` is the hash of the pathname at which the `i`th object +(counting in index order) in the pack can be found. This can be fed +into the delta heuristics to compare objects with similar pathnames. + +The hash algorithm used is: + + hash = 0; + while ((c = *name++)) + if (!isspace(c)) + hash = (hash >> 2) + (c << 24); + +Note that this hashing scheme is tied to the BITMAP_OPT_HASH_CACHE flag. +If implementations want to choose a different hashing scheme, they are +free to do so, but MUST allocate a new header flag (because comparing +hashes made under two different schemes would be pointless). diff --git a/Documentation/technical/http-protocol.txt b/Documentation/technical/http-protocol.txt new file mode 100644 index 0000000000..1c561bdd92 --- /dev/null +++ b/Documentation/technical/http-protocol.txt @@ -0,0 +1,507 @@ +HTTP transfer protocols +======================= + +Git supports two HTTP based transfer protocols. A "dumb" protocol +which requires only a standard HTTP server on the server end of the +connection, and a "smart" protocol which requires a Git aware CGI +(or server module). This document describes both protocols. + +As a design feature smart clients can automatically upgrade "dumb" +protocol URLs to smart URLs. This permits all users to have the +same published URL, and the peers automatically select the most +efficient transport available to them. + + +URL Format +---------- + +URLs for Git repositories accessed by HTTP use the standard HTTP +URL syntax documented by RFC 1738, so they are of the form: + + http://<host>:<port>/<path>?<searchpart> + +Within this documentation the placeholder `$GIT_URL` will stand for +the http:// repository URL entered by the end-user. + +Servers SHOULD handle all requests to locations matching `$GIT_URL`, as +both the "smart" and "dumb" HTTP protocols used by Git operate +by appending additional path components onto the end of the user +supplied `$GIT_URL` string. + +An example of a dumb client requesting for a loose object: + + $GIT_URL: http://example.com:8080/git/repo.git + URL request: http://example.com:8080/git/repo.git/objects/d0/49f6c27a2244e12041955e262a404c7faba355 + +An example of a smart request to a catch-all gateway: + + $GIT_URL: http://example.com/daemon.cgi?svc=git&q= + URL request: http://example.com/daemon.cgi?svc=git&q=/info/refs&service=git-receive-pack + +An example of a request to a submodule: + + $GIT_URL: http://example.com/git/repo.git/path/submodule.git + URL request: http://example.com/git/repo.git/path/submodule.git/info/refs + +Clients MUST strip a trailing `/`, if present, from the user supplied +`$GIT_URL` string to prevent empty path tokens (`//`) from appearing +in any URL sent to a server. Compatible clients MUST expand +`$GIT_URL/info/refs` as `foo/info/refs` and not `foo//info/refs`. + + +Authentication +-------------- + +Standard HTTP authentication is used if authentication is required +to access a repository, and MAY be configured and enforced by the +HTTP server software. + +Because Git repositories are accessed by standard path components +server administrators MAY use directory based permissions within +their HTTP server to control repository access. + +Clients SHOULD support Basic authentication as described by RFC 2617. +Servers SHOULD support Basic authentication by relying upon the +HTTP server placed in front of the Git server software. + +Servers SHOULD NOT require HTTP cookies for the purposes of +authentication or access control. + +Clients and servers MAY support other common forms of HTTP based +authentication, such as Digest authentication. + + +SSL +--- + +Clients and servers SHOULD support SSL, particularly to protect +passwords when relying on Basic HTTP authentication. + + +Session State +------------- + +The Git over HTTP protocol (much like HTTP itself) is stateless +from the perspective of the HTTP server side. All state MUST be +retained and managed by the client process. This permits simple +round-robin load-balancing on the server side, without needing to +worry about state management. + +Clients MUST NOT require state management on the server side in +order to function correctly. + +Servers MUST NOT require HTTP cookies in order to function correctly. +Clients MAY store and forward HTTP cookies during request processing +as described by RFC 2616 (HTTP/1.1). Servers SHOULD ignore any +cookies sent by a client. + + +General Request Processing +-------------------------- + +Except where noted, all standard HTTP behavior SHOULD be assumed +by both client and server. This includes (but is not necessarily +limited to): + +If there is no repository at `$GIT_URL`, or the resource pointed to by a +location matching `$GIT_URL` does not exist, the server MUST NOT respond +with `200 OK` response. A server SHOULD respond with +`404 Not Found`, `410 Gone`, or any other suitable HTTP status code +which does not imply the resource exists as requested. + +If there is a repository at `$GIT_URL`, but access is not currently +permitted, the server MUST respond with the `403 Forbidden` HTTP +status code. + +Servers SHOULD support both HTTP 1.0 and HTTP 1.1. +Servers SHOULD support chunked encoding for both request and response +bodies. + +Clients SHOULD support both HTTP 1.0 and HTTP 1.1. +Clients SHOULD support chunked encoding for both request and response +bodies. + +Servers MAY return ETag and/or Last-Modified headers. + +Clients MAY revalidate cached entities by including If-Modified-Since +and/or If-None-Match request headers. + +Servers MAY return `304 Not Modified` if the relevant headers appear +in the request and the entity has not changed. Clients MUST treat +`304 Not Modified` identical to `200 OK` by reusing the cached entity. + +Clients MAY reuse a cached entity without revalidation if the +Cache-Control and/or Expires header permits caching. Clients and +servers MUST follow RFC 2616 for cache controls. + + +Discovering References +---------------------- + +All HTTP clients MUST begin either a fetch or a push exchange by +discovering the references available on the remote repository. + +Dumb Clients +~~~~~~~~~~~~ + +HTTP clients that only support the "dumb" protocol MUST discover +references by making a request for the special info/refs file of +the repository. + +Dumb HTTP clients MUST make a `GET` request to `$GIT_URL/info/refs`, +without any search/query parameters. + + C: GET $GIT_URL/info/refs HTTP/1.0 + + S: 200 OK + S: + S: 95dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint + S: d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master + S: 2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0 + S: a3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{} + +The Content-Type of the returned info/refs entity SHOULD be +`text/plain; charset=utf-8`, but MAY be any content type. +Clients MUST NOT attempt to validate the returned Content-Type. +Dumb servers MUST NOT return a return type starting with +`application/x-git-`. + +Cache-Control headers MAY be returned to disable caching of the +returned entity. + +When examining the response clients SHOULD only examine the HTTP +status code. Valid responses are `200 OK`, or `304 Not Modified`. + +The returned content is a UNIX formatted text file describing +each ref and its known value. The file SHOULD be sorted by name +according to the C locale ordering. The file SHOULD NOT include +the default ref named `HEAD`. + + info_refs = *( ref_record ) + ref_record = any_ref / peeled_ref + + any_ref = obj-id HTAB refname LF + peeled_ref = obj-id HTAB refname LF + obj-id HTAB refname "^{}" LF + +Smart Clients +~~~~~~~~~~~~~ + +HTTP clients that support the "smart" protocol (or both the +"smart" and "dumb" protocols) MUST discover references by making +a parameterized request for the info/refs file of the repository. + +The request MUST contain exactly one query parameter, +`service=$servicename`, where `$servicename` MUST be the service +name the client wishes to contact to complete the operation. +The request MUST NOT contain additional query parameters. + + C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0 + +dumb server reply: + + S: 200 OK + S: + S: 95dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint + S: d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master + S: 2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0 + S: a3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{} + +smart server reply: + + S: 200 OK + S: Content-Type: application/x-git-upload-pack-advertisement + S: Cache-Control: no-cache + S: + S: 001e# service=git-upload-pack\n + S: 004895dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint\0multi_ack\n + S: 0042d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master\n + S: 003c2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0\n + S: 003fa3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{}\n + +Dumb Server Response +^^^^^^^^^^^^^^^^^^^^ +Dumb servers MUST respond with the dumb server reply format. + +See the prior section under dumb clients for a more detailed +description of the dumb server response. + +Smart Server Response +^^^^^^^^^^^^^^^^^^^^^ +If the server does not recognize the requested service name, or the +requested service name has been disabled by the server administrator, +the server MUST respond with the `403 Forbidden` HTTP status code. + +Otherwise, smart servers MUST respond with the smart server reply +format for the requested service name. + +Cache-Control headers SHOULD be used to disable caching of the +returned entity. + +The Content-Type MUST be `application/x-$servicename-advertisement`. +Clients SHOULD fall back to the dumb protocol if another content +type is returned. When falling back to the dumb protocol clients +SHOULD NOT make an additional request to `$GIT_URL/info/refs`, but +instead SHOULD use the response already in hand. Clients MUST NOT +continue if they do not support the dumb protocol. + +Clients MUST validate the status code is either `200 OK` or +`304 Not Modified`. + +Clients MUST validate the first five bytes of the response entity +matches the regex `^[0-9a-f]{4}#`. If this test fails, clients +MUST NOT continue. + +Clients MUST parse the entire response as a sequence of pkt-line +records. + +Clients MUST verify the first pkt-line is `# service=$servicename`. +Servers MUST set $servicename to be the request parameter value. +Servers SHOULD include an LF at the end of this line. +Clients MUST ignore an LF at the end of the line. + +Servers MUST terminate the response with the magic `0000` end +pkt-line marker. + +The returned response is a pkt-line stream describing each ref and +its known value. The stream SHOULD be sorted by name according to +the C locale ordering. The stream SHOULD include the default ref +named `HEAD` as the first ref. The stream MUST include capability +declarations behind a NUL on the first ref. + + smart_reply = PKT-LINE("# service=$servicename" LF) + ref_list + "0000" + ref_list = empty_list / non_empty_list + + empty_list = PKT-LINE(zero-id SP "capabilities^{}" NUL cap-list LF) + + non_empty_list = PKT-LINE(obj-id SP name NUL cap_list LF) + *ref_record + + cap-list = capability *(SP capability) + capability = 1*(LC_ALPHA / DIGIT / "-" / "_") + LC_ALPHA = %x61-7A + + ref_record = any_ref / peeled_ref + any_ref = PKT-LINE(obj-id SP name LF) + peeled_ref = PKT-LINE(obj-id SP name LF) + PKT-LINE(obj-id SP name "^{}" LF + + +Smart Service git-upload-pack +------------------------------ +This service reads from the repository pointed to by `$GIT_URL`. + +Clients MUST first perform ref discovery with +`$GIT_URL/info/refs?service=git-upload-pack`. + + C: POST $GIT_URL/git-upload-pack HTTP/1.0 + C: Content-Type: application/x-git-upload-pack-request + C: + C: 0032want 0a53e9ddeaddad63ad106860237bbf53411d11a7\n + C: 0032have 441b40d833fdfa93eb2908e52742248faf0ee993\n + C: 0000 + + S: 200 OK + S: Content-Type: application/x-git-upload-pack-result + S: Cache-Control: no-cache + S: + S: ....ACK %s, continue + S: ....NAK + +Clients MUST NOT reuse or revalidate a cached response. +Servers MUST include sufficient Cache-Control headers +to prevent caching of the response. + +Servers SHOULD support all capabilities defined here. + +Clients MUST send at least one "want" command in the request body. +Clients MUST NOT reference an id in a "want" command which did not +appear in the response obtained through ref discovery unless the +server advertises capability `allow-tip-sha1-in-want` or +`allow-reachable-sha1-in-want`. + + compute_request = want_list + have_list + request_end + request_end = "0000" / "done" + + want_list = PKT-LINE(want NUL cap_list LF) + *(want_pkt) + want_pkt = PKT-LINE(want LF) + want = "want" SP id + cap_list = *(SP capability) SP + + have_list = *PKT-LINE("have" SP id LF) + +TODO: Document this further. + +The Negotiation Algorithm +~~~~~~~~~~~~~~~~~~~~~~~~~ +The computation to select the minimal pack proceeds as follows +(C = client, S = server): + +'init step:' + +C: Use ref discovery to obtain the advertised refs. + +C: Place any object seen into set `advertised`. + +C: Build an empty set, `common`, to hold the objects that are later + determined to be on both ends. + +C: Build a set, `want`, of the objects from `advertised` the client + wants to fetch, based on what it saw during ref discovery. + +C: Start a queue, `c_pending`, ordered by commit time (popping newest + first). Add all client refs. When a commit is popped from + the queue its parents SHOULD be automatically inserted back. + Commits MUST only enter the queue once. + +'one compute step:' + +C: Send one `$GIT_URL/git-upload-pack` request: + + C: 0032want <want #1>............................... + C: 0032want <want #2>............................... + .... + C: 0032have <common #1>............................. + C: 0032have <common #2>............................. + .... + C: 0032have <have #1>............................... + C: 0032have <have #2>............................... + .... + C: 0000 + +The stream is organized into "commands", with each command +appearing by itself in a pkt-line. Within a command line, +the text leading up to the first space is the command name, +and the remainder of the line to the first LF is the value. +Command lines are terminated with an LF as the last byte of +the pkt-line value. + +Commands MUST appear in the following order, if they appear +at all in the request stream: + +* "want" +* "have" + +The stream is terminated by a pkt-line flush (`0000`). + +A single "want" or "have" command MUST have one hex formatted +SHA-1 as its value. Multiple SHA-1s MUST be sent by sending +multiple commands. + +The `have` list is created by popping the first 32 commits +from `c_pending`. Less can be supplied if `c_pending` empties. + +If the client has sent 256 "have" commits and has not yet +received one of those back from `s_common`, or the client has +emptied `c_pending` it SHOULD include a "done" command to let +the server know it won't proceed: + + C: 0009done + +S: Parse the git-upload-pack request: + +Verify all objects in `want` are directly reachable from refs. + +The server MAY walk backwards through history or through +the reflog to permit slightly stale requests. + +If no "want" objects are received, send an error: +TODO: Define error if no "want" lines are requested. + +If any "want" object is not reachable, send an error: +TODO: Define error if an invalid "want" is requested. + +Create an empty list, `s_common`. + +If "have" was sent: + +Loop through the objects in the order supplied by the client. + +For each object, if the server has the object reachable from +a ref, add it to `s_common`. If a commit is added to `s_common`, +do not add any ancestors, even if they also appear in `have`. + +S: Send the git-upload-pack response: + +If the server has found a closed set of objects to pack or the +request ends with "done", it replies with the pack. +TODO: Document the pack based response + + S: PACK... + +The returned stream is the side-band-64k protocol supported +by the git-upload-pack service, and the pack is embedded into +stream 1. Progress messages from the server side MAY appear +in stream 2. + +Here a "closed set of objects" is defined to have at least +one path from every "want" to at least one "common" object. + +If the server needs more information, it replies with a +status continue response: +TODO: Document the non-pack response + +C: Parse the upload-pack response: + TODO: Document parsing response + +'Do another compute step.' + + +Smart Service git-receive-pack +------------------------------ +This service reads from the repository pointed to by `$GIT_URL`. + +Clients MUST first perform ref discovery with +`$GIT_URL/info/refs?service=git-receive-pack`. + + C: POST $GIT_URL/git-receive-pack HTTP/1.0 + C: Content-Type: application/x-git-receive-pack-request + C: + C: ....0a53e9ddeaddad63ad106860237bbf53411d11a7 441b40d833fdfa93eb2908e52742248faf0ee993 refs/heads/maint\0 report-status + C: 0000 + C: PACK.... + + S: 200 OK + S: Content-Type: application/x-git-receive-pack-result + S: Cache-Control: no-cache + S: + S: .... + +Clients MUST NOT reuse or revalidate a cached response. +Servers MUST include sufficient Cache-Control headers +to prevent caching of the response. + +Servers SHOULD support all capabilities defined here. + +Clients MUST send at least one command in the request body. +Within the command portion of the request body clients SHOULD send +the id obtained through ref discovery as old_id. + + update_request = command_list + "PACK" <binary data> + + command_list = PKT-LINE(command NUL cap_list LF) + *(command_pkt) + command_pkt = PKT-LINE(command LF) + cap_list = *(SP capability) SP + + command = create / delete / update + create = zero-id SP new_id SP name + delete = old_id SP zero-id SP name + update = old_id SP new_id SP name + +TODO: Document this further. + + +References +---------- + +http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)] +http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1] +link:technical/pack-protocol.html +link:technical/protocol-capabilities.html diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt new file mode 100644 index 0000000000..7392ff636c --- /dev/null +++ b/Documentation/technical/index-format.txt @@ -0,0 +1,297 @@ +Git index format +================ + +== The Git index file has the following format + + All binary numbers are in network byte order. Version 2 is described + here unless stated otherwise. + + - A 12-byte header consisting of + + 4-byte signature: + The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache") + + 4-byte version number: + The current supported versions are 2, 3 and 4. + + 32-bit number of index entries. + + - A number of sorted index entries (see below). + + - Extensions + + Extensions are identified by signature. Optional extensions can + be ignored if Git does not understand them. + + Git currently supports cached tree and resolve undo extensions. + + 4-byte extension signature. If the first byte is 'A'..'Z' the + extension is optional and can be ignored. + + 32-bit size of the extension + + Extension data + + - 160-bit SHA-1 over the content of the index file before this + checksum. + +== Index entry + + Index entries are sorted in ascending order on the name field, + interpreted as a string of unsigned bytes (i.e. memcmp() order, no + localization, no special casing of directory separator '/'). Entries + with the same name are sorted by their stage field. + + 32-bit ctime seconds, the last time a file's metadata changed + this is stat(2) data + + 32-bit ctime nanosecond fractions + this is stat(2) data + + 32-bit mtime seconds, the last time a file's data changed + this is stat(2) data + + 32-bit mtime nanosecond fractions + this is stat(2) data + + 32-bit dev + this is stat(2) data + + 32-bit ino + this is stat(2) data + + 32-bit mode, split into (high to low bits) + + 4-bit object type + valid values in binary are 1000 (regular file), 1010 (symbolic link) + and 1110 (gitlink) + + 3-bit unused + + 9-bit unix permission. Only 0755 and 0644 are valid for regular files. + Symbolic links and gitlinks have value 0 in this field. + + 32-bit uid + this is stat(2) data + + 32-bit gid + this is stat(2) data + + 32-bit file size + This is the on-disk size from stat(2), truncated to 32-bit. + + 160-bit SHA-1 for the represented object + + A 16-bit 'flags' field split into (high to low bits) + + 1-bit assume-valid flag + + 1-bit extended flag (must be zero in version 2) + + 2-bit stage (during merge) + + 12-bit name length if the length is less than 0xFFF; otherwise 0xFFF + is stored in this field. + + (Version 3 or later) A 16-bit field, only applicable if the + "extended flag" above is 1, split into (high to low bits). + + 1-bit reserved for future + + 1-bit skip-worktree flag (used by sparse checkout) + + 1-bit intent-to-add flag (used by "git add -N") + + 13-bit unused, must be zero + + Entry path name (variable length) relative to top level directory + (without leading slash). '/' is used as path separator. The special + path components ".", ".." and ".git" (without quotes) are disallowed. + Trailing slash is also disallowed. + + The exact encoding is undefined, but the '.' and '/' characters + are encoded in 7-bit ASCII and the encoding cannot contain a NUL + byte (iow, this is a UNIX pathname). + + (Version 4) In version 4, the entry path name is prefix-compressed + relative to the path name for the previous entry (the very first + entry is encoded as if the path name for the previous entry is an + empty string). At the beginning of an entry, an integer N in the + variable width encoding (the same encoding as the offset is encoded + for OFS_DELTA pack entries; see pack-format.txt) is stored, followed + by a NUL-terminated string S. Removing N bytes from the end of the + path name for the previous entry, and replacing it with the string S + yields the path name for this entry. + + 1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes + while keeping the name NUL-terminated. + + (Version 4) In version 4, the padding after the pathname does not + exist. + + Interpretation of index entries in split index mode is completely + different. See below for details. + +== Extensions + +=== Cached tree + + Cached tree extension contains pre-computed hashes for trees that can + be derived from the index. It helps speed up tree object generation + from index for a new commit. + + When a path is updated in index, the path must be invalidated and + removed from tree cache. + + The signature for this extension is { 'T', 'R', 'E', 'E' }. + + A series of entries fill the entire extension; each of which + consists of: + + - NUL-terminated path component (relative to its parent directory); + + - ASCII decimal number of entries in the index that is covered by the + tree this entry represents (entry_count); + + - A space (ASCII 32); + + - ASCII decimal number that represents the number of subtrees this + tree has; + + - A newline (ASCII 10); and + + - 160-bit object name for the object that would result from writing + this span of index as a tree. + + An entry can be in an invalidated state and is represented by having + a negative number in the entry_count field. In this case, there is no + object name and the next entry starts immediately after the newline. + When writing an invalid entry, -1 should always be used as entry_count. + + The entries are written out in the top-down, depth-first order. The + first entry represents the root level of the repository, followed by the + first subtree---let's call this A---of the root level (with its name + relative to the root level), followed by the first subtree of A (with + its name relative to A), ... + +=== Resolve undo + + A conflict is represented in the index as a set of higher stage entries. + When a conflict is resolved (e.g. with "git add path"), these higher + stage entries will be removed and a stage-0 entry with proper resolution + is added. + + When these higher stage entries are removed, they are saved in the + resolve undo extension, so that conflicts can be recreated (e.g. with + "git checkout -m"), in case users want to redo a conflict resolution + from scratch. + + The signature for this extension is { 'R', 'E', 'U', 'C' }. + + A series of entries fill the entire extension; each of which + consists of: + + - NUL-terminated pathname the entry describes (relative to the root of + the repository, i.e. full pathname); + + - Three NUL-terminated ASCII octal numbers, entry mode of entries in + stage 1 to 3 (a missing stage is represented by "0" in this field); + and + + - At most three 160-bit object names of the entry in stages from 1 to 3 + (nothing is written for a missing stage). + +=== Split index + + In split index mode, the majority of index entries could be stored + in a separate file. This extension records the changes to be made on + top of that to produce the final index. + + The signature for this extension is { 'l', 'i', 'n', 'k' }. + + The extension consists of: + + - 160-bit SHA-1 of the shared index file. The shared index file path + is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the + index does not require a shared index file. + + - An ewah-encoded delete bitmap, each bit represents an entry in the + shared index. If a bit is set, its corresponding entry in the + shared index will be removed from the final index. Note, because + a delete operation changes index entry positions, but we do need + original positions in replace phase, it's best to just mark + entries for removal, then do a mass deletion after replacement. + + - An ewah-encoded replace bitmap, each bit represents an entry in + the shared index. If a bit is set, its corresponding entry in the + shared index will be replaced with an entry in this index + file. All replaced entries are stored in sorted order in this + index. The first "1" bit in the replace bitmap corresponds to the + first index entry, the second "1" bit to the second entry and so + on. Replaced entries may have empty path names to save space. + + The remaining index entries after replaced ones will be added to the + final index. These added entries are also sorted by entry name then + stage. + +== Untracked cache + + Untracked cache saves the untracked file list and necessary data to + verify the cache. The signature for this extension is { 'U', 'N', + 'T', 'R' }. + + The extension starts with + + - A sequence of NUL-terminated strings, preceded by the size of the + sequence in variable width encoding. Each string describes the + environment where the cache can be used. + + - Stat data of $GIT_DIR/info/exclude. See "Index entry" section from + ctime field until "file size". + + - Stat data of core.excludesfile + + - 32-bit dir_flags (see struct dir_struct) + + - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file + does not exist. + + - 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does + not exist. + + - NUL-terminated string of per-dir exclude file name. This usually + is ".gitignore". + + - The number of following directory blocks, variable width + encoding. If this number is zero, the extension ends here with a + following NUL. + + - A number of directory blocks in depth-first-search order, each + consists of + + - The number of untracked entries, variable width encoding. + + - The number of sub-directory blocks, variable width encoding. + + - The directory name terminated by NUL. + + - A number of untracked file/dir names terminated by NUL. + +The remaining data of each directory block is grouped by type: + + - An ewah bitmap, the n-th bit marks whether the n-th directory has + valid untracked cache entries. + + - An ewah bitmap, the n-th bit records "check-only" bit of + read_directory_recursive() for the n-th directory. + + - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data + is valid for the n-th directory and exists in the next data. + + - An array of stat data. The n-th data corresponds with the n-th + "one" bit in the previous ewah bitmap. + + - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit + in the previous ewah bitmap. + + - One NUL. diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index e5b31c81fa..8e5bf60be3 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -1,15 +1,15 @@ -GIT pack format +Git pack format =============== -= pack-*.pack file has the following format: +== pack-*.pack files have the following format: - - The header appears at the beginning and consists of the following: + - A header appears at the beginning and consists of the following: 4-byte signature: The signature is: {'P', 'A', 'C', 'K'} 4-byte version number (network byte order): - GIT currently accepts version number 2 or 3 but + Git currently accepts version number 2 or 3 but generates version 2 only. 4-byte number of objects contained in the pack (network byte order) @@ -26,26 +26,24 @@ GIT pack format (deltified representation) n-byte type and length (3-bit type, (n-1)*7+4-bit length) - 20-byte base object name + 20-byte base object name if OBJ_REF_DELTA or a negative relative + offset from the delta object's position in the pack if this + is an OBJ_OFS_DELTA object compressed delta data Observation: length of each object is encoded in a variable length format and is not constrained to 32-bit or anything. - - The trailer records 20-byte SHA1 checksum of all of the above. + - The trailer records 20-byte SHA-1 checksum of all of the above. -= pack-*.idx file has the following format: +== Original (version 1) pack-*.idx files have the following format: - The header consists of 256 4-byte network byte order integers. N-th entry of this table records the number of objects in the corresponding pack, the first byte of whose - object name are smaller than N. This is called the + object name is less than or equal to N. This is called the 'first-level fan-out' table. - Observation: we would need to extend this to an array of - 8-byte integers to go beyond 4G objects per pack, but it is - not strictly necessary. - - The header is followed by sorted 24-byte entries, one entry per object in the pack. Each entry is: @@ -55,44 +53,39 @@ GIT pack format 20-byte object name. - Observation: we would definitely need to extend this to - 8-byte integer plus 20-byte object name to handle a packfile - that is larger than 4GB. - - The file is concluded with a trailer: - A copy of the 20-byte SHA1 checksum at the end of + A copy of the 20-byte SHA-1 checksum at the end of corresponding packfile. - 20-byte SHA1-checksum of all of the above. + 20-byte SHA-1-checksum of all of the above. Pack Idx file: - idx - +--------------------------------+ - | fanout[0] = 2 |-. - +--------------------------------+ | + -- +--------------------------------+ +fanout | fanout[0] = 2 (for example) |-. +table +--------------------------------+ | | fanout[1] | | +--------------------------------+ | | fanout[2] | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | - | fanout[255] | | - +--------------------------------+ | -main | offset | | -index | object name 00XXXXXXXXXXXXXXXX | | -table +--------------------------------+ | - | offset | | - | object name 00XXXXXXXXXXXXXXXX | | - +--------------------------------+ | - .-| offset |<+ - | | object name 01XXXXXXXXXXXXXXXX | - | +--------------------------------+ - | | offset | - | | object name 01XXXXXXXXXXXXXXXX | - | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - | | offset | - | | object name FFXXXXXXXXXXXXXXXX | - | +--------------------------------+ + | fanout[255] = total objects |---. + -- +--------------------------------+ | | +main | offset | | | +index | object name 00XXXXXXXXXXXXXXXX | | | +table +--------------------------------+ | | + | offset | | | + | object name 00XXXXXXXXXXXXXXXX | | | + +--------------------------------+<+ | + .-| offset | | + | | object name 01XXXXXXXXXXXXXXXX | | + | +--------------------------------+ | + | | offset | | + | | object name 01XXXXXXXXXXXXXXXX | | + | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | + | | offset | | + | | object name FFXXXXXXXXXXXXXXXX | | + --| +--------------------------------+<--+ trailer | | packfile checksum | | +--------------------------------+ | | idxfile checksum | @@ -112,7 +105,58 @@ Pack file entry: <+ packed object data: If it is not DELTA, then deflated bytes (the size above is the size before compression). - If it is DELTA, then - 20-byte base object name SHA1 (the size above is the + If it is REF_DELTA, then + 20-byte base object name SHA-1 (the size above is the size of the delta data that follows). delta data, deflated. + If it is OFS_DELTA, then + n-byte offset (see below) interpreted as a negative + offset from the type-byte of the header of the + ofs-delta entry (the size above is the size of + the delta data that follows). + delta data, deflated. + + offset encoding: + n bytes with MSB set in all but the last one. + The offset is then the number constructed by + concatenating the lower 7 bit of each byte, and + for n >= 2 adding 2^7 + 2^14 + ... + 2^(7*(n-1)) + to the result. + + + +== Version 2 pack-*.idx files support packs larger than 4 GiB, and + have some other reorganizations. They have the format: + + - A 4-byte magic number '\377tOc' which is an unreasonable + fanout[0] value. + + - A 4-byte version number (= 2) + + - A 256-entry fan-out table just like v1. + + - A table of sorted 20-byte SHA-1 object names. These are + packed together without offset values to reduce the cache + footprint of the binary search for a specific object name. + + - A table of 4-byte CRC32 values of the packed object data. + This is new in v2 so compressed data can be copied directly + from pack to pack during repacking without undetected + data corruption. + + - A table of 4-byte offset values (in network byte order). + These are usually 31-bit pack file offsets, but large + offsets are encoded as an index into the next table with + the msbit set. + + - A table of 8-byte offset entries (empty for pack files less + than 2 GiB). Pack files are organized with heavily used + objects toward the front, so most object references should + not need to refer to this table. + + - The same trailer as a v1 pack file: + + A copy of the 20-byte SHA-1 checksum at the end of + corresponding packfile. + + 20-byte SHA-1-checksum of all of the above. diff --git a/Documentation/technical/pack-heuristics.txt b/Documentation/technical/pack-heuristics.txt index 103eb5d989..95a07db6e8 100644 --- a/Documentation/technical/pack-heuristics.txt +++ b/Documentation/technical/pack-heuristics.txt @@ -1,15 +1,15 @@ - Concerning Git's Packing Heuristics - =================================== +Concerning Git's Packing Heuristics +=================================== Oh, here's a really stupid question: Where do I go to learn the details - of git's packing heuristics? + of Git's packing heuristics? Be careful what you ask! -Followers of the git, please open the git IRC Log and turn to +Followers of the Git, please open the Git IRC Log and turn to February 10, 2006. It's a rare occasion, and we are joined by the King Git Himself, @@ -19,7 +19,7 @@ and seeks enlightenment. Others are present, but silent. Let's listen in! <njs`> Oh, here's a really stupid question -- where do I go to - learn the details of git's packing heuristics? google avails + learn the details of Git's packing heuristics? google avails me not, reading the source didn't help a lot, and wading through the whole mailing list seems less efficient than any of that. @@ -37,7 +37,7 @@ Ah! Modesty after all. <linus> njs, I don't think the docs exist. That's something where I don't think anybody else than me even really got involved. - Most of the rest of git others have been busy with (especially + Most of the rest of Git others have been busy with (especially Junio), but packing nobody touched after I did it. It's cryptic, yet vague. Linus in style for sure. Wise men @@ -57,7 +57,7 @@ Bait... And switch. That ought to do it! - <linus> Remember: git really doesn't follow files. So what it does is + <linus> Remember: Git really doesn't follow files. So what it does is - generate a list of all objects - sort the list according to magic heuristics - walk the list, using a sliding window, seeing if an object @@ -89,7 +89,7 @@ Ah, grasshopper! And thus the enlightenment begins anew. <linus> The "magic" is actually in theory totally arbitrary. ANY order will give you a working pack, but no, it's not - ordered by SHA1. + ordered by SHA-1. Before talking about the ordering for the sliding delta window, let's talk about the recency order. That's more @@ -366,12 +366,6 @@ been detailed! <linus> Yes, we always write out most recent first -For the other record: - - <pasky> njs`: http://pastebin.com/547965 - -The 'net never forgets, so that should be good until the end of time. - <njs`> And, yeah, I got the part about deeper-in-history stuff having worse IO characteristics, one sort of doesn't care. @@ -382,7 +376,7 @@ The 'net never forgets, so that should be good until the end of time. <njs`> (if only it happened more...) <linus> Anyway, the pack-file could easily be denser still, but - because it's used both for streaming (the git protocol) and + because it's used both for streaming (the Git protocol) and for on-disk, it has a few pessimizations. Actually, it is a made-up word. But it is a made-up word being @@ -432,12 +426,12 @@ Gasp! OK, saved. That's a fair Engineering trade off. Close call! In fact, Linus reflects on some Basic Engineering Fundamentals, design options, etc. - <linus> More importantly, they allow git to still _conceptually_ + <linus> More importantly, they allow Git to still _conceptually_ never deal with deltas at all, and be a "whole object" store. Which has some problems (we discussed bad huge-file - behaviour on the git lists the other day), but it does mean - that the basic git concepts are really really simple and + behaviour on the Git lists the other day), but it does mean + that the basic Git concepts are really really simple and straightforward. It's all been quite stable. @@ -461,6 +455,6 @@ Nuff said. <njs`> :-) <njs`> appreciate the infodump, I really was failing to find the - details on git packs :-) + details on Git packs :-) And now you know the rest of the story. diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt index 9cd48b4859..4064fc796f 100644 --- a/Documentation/technical/pack-protocol.txt +++ b/Documentation/technical/pack-protocol.txt @@ -1,41 +1,597 @@ -Pack transfer protocols -======================= - -There are two Pack push-pull protocols. - -upload-pack (S) | fetch/clone-pack (C) protocol: - - # Tell the puller what commits we have and what their names are - S: SHA1 name - S: ... - S: SHA1 name - S: # flush -- it's your turn - # Tell the pusher what commits we want, and what we have - C: want name - C: .. - C: want name - C: have SHA1 - C: have SHA1 - C: ... - C: # flush -- occasionally ask "had enough?" - S: NAK - C: have SHA1 - C: ... - C: have SHA1 - S: ACK - C: done - S: XXXXXXX -- packfile contents. - -send-pack | receive-pack protocol. - - # Tell the pusher what commits we have and what their names are - C: SHA1 name - C: ... - C: SHA1 name - C: # flush -- it's your turn - # Tell the puller what the pusher has - S: old-SHA1 new-SHA1 name - S: old-SHA1 new-SHA1 name - S: ... - S: # flush -- done with the list - S: XXXXXXX --- packfile contents. +Packfile transfer protocols +=========================== + +Git supports transferring data in packfiles over the ssh://, git://, http:// and +file:// transports. There exist two sets of protocols, one for pushing +data from a client to a server and another for fetching data from a +server to a client. The three transports (ssh, git, file) use the same +protocol to transfer data. http is documented in http-protocol.txt. + +The processes invoked in the canonical Git implementation are 'upload-pack' +on the server side and 'fetch-pack' on the client side for fetching data; +then 'receive-pack' on the server and 'send-pack' on the client for pushing +data. The protocol functions to have a server tell a client what is +currently on the server, then for the two to negotiate the smallest amount +of data to send in order to fully update one or the other. + +Transports +---------- +There are three transports over which the packfile protocol is +initiated. The Git transport is a simple, unauthenticated server that +takes the command (almost always 'upload-pack', though Git +servers can be configured to be globally writable, in which 'receive- +pack' initiation is also allowed) with which the client wishes to +communicate and executes it and connects it to the requesting +process. + +In the SSH transport, the client just runs the 'upload-pack' +or 'receive-pack' process on the server over the SSH protocol and then +communicates with that invoked process over the SSH connection. + +The file:// transport runs the 'upload-pack' or 'receive-pack' +process locally and communicates with it over a pipe. + +Git Transport +------------- + +The Git transport starts off by sending the command and repository +on the wire using the pkt-line format, followed by a NUL byte and a +hostname parameter, terminated by a NUL byte. + + 0032git-upload-pack /project.git\0host=myserver.com\0 + +-- + git-proto-request = request-command SP pathname NUL [ host-parameter NUL ] + request-command = "git-upload-pack" / "git-receive-pack" / + "git-upload-archive" ; case sensitive + pathname = *( %x01-ff ) ; exclude NUL + host-parameter = "host=" hostname [ ":" port ] +-- + +Only host-parameter is allowed in the git-proto-request. Clients +MUST NOT attempt to send additional parameters. It is used for the +git-daemon name based virtual hosting. See --interpolated-path +option to git daemon, with the %H/%CH format characters. + +Basically what the Git client is doing to connect to an 'upload-pack' +process on the server side over the Git protocol is this: + + $ echo -e -n \ + "0039git-upload-pack /schacon/gitbook.git\0host=example.com\0" | + nc -v example.com 9418 + +If the server refuses the request for some reasons, it could abort +gracefully with an error message. + +---- + error-line = PKT-LINE("ERR" SP explanation-text) +---- + + +SSH Transport +------------- + +Initiating the upload-pack or receive-pack processes over SSH is +executing the binary on the server via SSH remote execution. +It is basically equivalent to running this: + + $ ssh git.example.com "git-upload-pack '/project.git'" + +For a server to support Git pushing and pulling for a given user over +SSH, that user needs to be able to execute one or both of those +commands via the SSH shell that they are provided on login. On some +systems, that shell access is limited to only being able to run those +two commands, or even just one of them. + +In an ssh:// format URI, it's absolute in the URI, so the '/' after +the host name (or port number) is sent as an argument, which is then +read by the remote git-upload-pack exactly as is, so it's effectively +an absolute path in the remote filesystem. + + git clone ssh://user@example.com/project.git + | + v + ssh user@example.com "git-upload-pack '/project.git'" + +In a "user@host:path" format URI, its relative to the user's home +directory, because the Git client will run: + + git clone user@example.com:project.git + | + v + ssh user@example.com "git-upload-pack 'project.git'" + +The exception is if a '~' is used, in which case +we execute it without the leading '/'. + + ssh://user@example.com/~alice/project.git, + | + v + ssh user@example.com "git-upload-pack '~alice/project.git'" + +A few things to remember here: + +- The "command name" is spelled with dash (e.g. git-upload-pack), but + this can be overridden by the client; + +- The repository path is always quoted with single quotes. + +Fetching Data From a Server +--------------------------- + +When one Git repository wants to get data that a second repository +has, the first can 'fetch' from the second. This operation determines +what data the server has that the client does not then streams that +data down to the client in packfile format. + + +Reference Discovery +------------------- + +When the client initially connects the server will immediately respond +with a listing of each reference it has (all branches and tags) along +with the object name that each reference currently points to. + + $ echo -e -n "0039git-upload-pack /schacon/gitbook.git\0host=example.com\0" | + nc -v example.com 9418 + 00887217a7c7e582c46cec22a130adf4b9d7d950fba0 HEAD\0multi_ack thin-pack + side-band side-band-64k ofs-delta shallow no-progress include-tag + 00441d3fcd5ced445d1abc402225c0b8a1299641f497 refs/heads/integration + 003f7217a7c7e582c46cec22a130adf4b9d7d950fba0 refs/heads/master + 003cb88d2441cac0977faf98efc80305012112238d9d refs/tags/v0.9 + 003c525128480b96c89e6418b1e40909bf6c5b2d580f refs/tags/v1.0 + 003fe92df48743b7bc7d26bcaabfddde0a1e20cae47c refs/tags/v1.0^{} + 0000 + +Server SHOULD terminate each non-flush line using LF ("\n") terminator; +client MUST NOT complain if there is no terminator. + +The returned response is a pkt-line stream describing each ref and +its current value. The stream MUST be sorted by name according to +the C locale ordering. + +If HEAD is a valid ref, HEAD MUST appear as the first advertised +ref. If HEAD is not a valid ref, HEAD MUST NOT appear in the +advertisement list at all, but other refs may still appear. + +The stream MUST include capability declarations behind a NUL on the +first ref. The peeled value of a ref (that is "ref^{}") MUST be +immediately after the ref itself, if presented. A conforming server +MUST peel the ref if it's an annotated tag. + +---- + advertised-refs = (no-refs / list-of-refs) + *shallow + flush-pkt + + no-refs = PKT-LINE(zero-id SP "capabilities^{}" + NUL capability-list LF) + + list-of-refs = first-ref *other-ref + first-ref = PKT-LINE(obj-id SP refname + NUL capability-list LF) + + other-ref = PKT-LINE(other-tip / other-peeled) + other-tip = obj-id SP refname LF + other-peeled = obj-id SP refname "^{}" LF + + shallow = PKT-LINE("shallow" SP obj-id) + + capability-list = capability *(SP capability) + capability = 1*(LC_ALPHA / DIGIT / "-" / "_") + LC_ALPHA = %x61-7A +---- + +Server and client MUST use lowercase for obj-id, both MUST treat obj-id +as case-insensitive. + +See protocol-capabilities.txt for a list of allowed server capabilities +and descriptions. + +Packfile Negotiation +-------------------- +After reference and capabilities discovery, the client can decide to +terminate the connection by sending a flush-pkt, telling the server it can +now gracefully terminate, and disconnect, when it does not need any pack +data. This can happen with the ls-remote command, and also can happen when +the client already is up-to-date. + +Otherwise, it enters the negotiation phase, where the client and +server determine what the minimal packfile necessary for transport is, +by telling the server what objects it wants, its shallow objects +(if any), and the maximum commit depth it wants (if any). The client +will also send a list of the capabilities it wants to be in effect, +out of what the server said it could do with the first 'want' line. + +---- + upload-request = want-list + *shallow-line + *1depth-request + flush-pkt + + want-list = first-want + *additional-want + + shallow-line = PKT-LINE("shallow" SP obj-id) + + depth-request = PKT-LINE("deepen" SP depth) + + first-want = PKT-LINE("want" SP obj-id SP capability-list LF) + additional-want = PKT-LINE("want" SP obj-id LF) + + depth = 1*DIGIT +---- + +Clients MUST send all the obj-ids it wants from the reference +discovery phase as 'want' lines. Clients MUST send at least one +'want' command in the request body. Clients MUST NOT mention an +obj-id in a 'want' command which did not appear in the response +obtained through ref discovery. + +The client MUST write all obj-ids which it only has shallow copies +of (meaning that it does not have the parents of a commit) as +'shallow' lines so that the server is aware of the limitations of +the client's history. + +The client now sends the maximum commit history depth it wants for +this transaction, which is the number of commits it wants from the +tip of the history, if any, as a 'deepen' line. A depth of 0 is the +same as not making a depth request. The client does not want to receive +any commits beyond this depth, nor does it want objects needed only to +complete those commits. Commits whose parents are not received as a +result are defined as shallow and marked as such in the server. This +information is sent back to the client in the next step. + +Once all the 'want's and 'shallow's (and optional 'deepen') are +transferred, clients MUST send a flush-pkt, to tell the server side +that it is done sending the list. + +Otherwise, if the client sent a positive depth request, the server +will determine which commits will and will not be shallow and +send this information to the client. If the client did not request +a positive depth, this step is skipped. + +---- + shallow-update = *shallow-line + *unshallow-line + flush-pkt + + shallow-line = PKT-LINE("shallow" SP obj-id) + + unshallow-line = PKT-LINE("unshallow" SP obj-id) +---- + +If the client has requested a positive depth, the server will compute +the set of commits which are no deeper than the desired depth. The set +of commits start at the client's wants. + +The server writes 'shallow' lines for each +commit whose parents will not be sent as a result. The server writes +an 'unshallow' line for each commit which the client has indicated is +shallow, but is no longer shallow at the currently requested depth +(that is, its parents will now be sent). The server MUST NOT mark +as unshallow anything which the client has not indicated was shallow. + +Now the client will send a list of the obj-ids it has using 'have' +lines, so the server can make a packfile that only contains the objects +that the client needs. In multi_ack mode, the canonical implementation +will send up to 32 of these at a time, then will send a flush-pkt. The +canonical implementation will skip ahead and send the next 32 immediately, +so that there is always a block of 32 "in-flight on the wire" at a time. + +---- + upload-haves = have-list + compute-end + + have-list = *have-line + have-line = PKT-LINE("have" SP obj-id LF) + compute-end = flush-pkt / PKT-LINE("done") +---- + +If the server reads 'have' lines, it then will respond by ACKing any +of the obj-ids the client said it had that the server also has. The +server will ACK obj-ids differently depending on which ack mode is +chosen by the client. + +In multi_ack mode: + + * the server will respond with 'ACK obj-id continue' for any common + commits. + + * once the server has found an acceptable common base commit and is + ready to make a packfile, it will blindly ACK all 'have' obj-ids + back to the client. + + * the server will then send a 'NACK' and then wait for another response + from the client - either a 'done' or another list of 'have' lines. + +In multi_ack_detailed mode: + + * the server will differentiate the ACKs where it is signaling + that it is ready to send data with 'ACK obj-id ready' lines, and + signals the identified common commits with 'ACK obj-id common' lines. + +Without either multi_ack or multi_ack_detailed: + + * upload-pack sends "ACK obj-id" on the first common object it finds. + After that it says nothing until the client gives it a "done". + + * upload-pack sends "NAK" on a flush-pkt if no common object + has been found yet. If one has been found, and thus an ACK + was already sent, it's silent on the flush-pkt. + +After the client has gotten enough ACK responses that it can determine +that the server has enough information to send an efficient packfile +(in the canonical implementation, this is determined when it has received +enough ACKs that it can color everything left in the --date-order queue +as common with the server, or the --date-order queue is empty), or the +client determines that it wants to give up (in the canonical implementation, +this is determined when the client sends 256 'have' lines without getting +any of them ACKed by the server - meaning there is nothing in common and +the server should just send all of its objects), then the client will send +a 'done' command. The 'done' command signals to the server that the client +is ready to receive its packfile data. + +However, the 256 limit *only* turns on in the canonical client +implementation if we have received at least one "ACK %s continue" +during a prior round. This helps to ensure that at least one common +ancestor is found before we give up entirely. + +Once the 'done' line is read from the client, the server will either +send a final 'ACK obj-id' or it will send a 'NAK'. 'obj-id' is the object +name of the last commit determined to be common. The server only sends +ACK after 'done' if there is at least one common base and multi_ack or +multi_ack_detailed is enabled. The server always sends NAK after 'done' +if there is no common base found. + +Then the server will start sending its packfile data. + +---- + server-response = *ack_multi ack / nak + ack_multi = PKT-LINE("ACK" SP obj-id ack_status LF) + ack_status = "continue" / "common" / "ready" + ack = PKT-LINE("ACK SP obj-id LF) + nak = PKT-LINE("NAK" LF) +---- + +A simple clone may look like this (with no 'have' lines): + +---- + C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \ + side-band-64k ofs-delta\n + C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\n + C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\n + C: 0032want 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\n + C: 0032want 74730d410fcb6603ace96f1dc55ea6196122532d\n + C: 0000 + C: 0009done\n + + S: 0008NAK\n + S: [PACKFILE] +---- + +An incremental update (fetch) response might look like this: + +---- + C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \ + side-band-64k ofs-delta\n + C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\n + C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\n + C: 0000 + C: 0032have 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\n + C: [30 more have lines] + C: 0032have 74730d410fcb6603ace96f1dc55ea6196122532d\n + C: 0000 + + S: 003aACK 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01 continue\n + S: 003aACK 74730d410fcb6603ace96f1dc55ea6196122532d continue\n + S: 0008NAK\n + + C: 0009done\n + + S: 0031ACK 74730d410fcb6603ace96f1dc55ea6196122532d\n + S: [PACKFILE] +---- + + +Packfile Data +------------- + +Now that the client and server have finished negotiation about what +the minimal amount of data that needs to be sent to the client is, the server +will construct and send the required data in packfile format. + +See pack-format.txt for what the packfile itself actually looks like. + +If 'side-band' or 'side-band-64k' capabilities have been specified by +the client, the server will send the packfile data multiplexed. + +Each packet starting with the packet-line length of the amount of data +that follows, followed by a single byte specifying the sideband the +following data is coming in on. + +In 'side-band' mode, it will send up to 999 data bytes plus 1 control +code, for a total of up to 1000 bytes in a pkt-line. In 'side-band-64k' +mode it will send up to 65519 data bytes plus 1 control code, for a +total of up to 65520 bytes in a pkt-line. + +The sideband byte will be a '1', '2' or a '3'. Sideband '1' will contain +packfile data, sideband '2' will be used for progress information that the +client will generally print to stderr and sideband '3' is used for error +information. + +If no 'side-band' capability was specified, the server will stream the +entire packfile without multiplexing. + + +Pushing Data To a Server +------------------------ + +Pushing data to a server will invoke the 'receive-pack' process on the +server, which will allow the client to tell it which references it should +update and then send all the data the server will need for those new +references to be complete. Once all the data is received and validated, +the server will then update its references to what the client specified. + +Authentication +-------------- + +The protocol itself contains no authentication mechanisms. That is to be +handled by the transport, such as SSH, before the 'receive-pack' process is +invoked. If 'receive-pack' is configured over the Git transport, those +repositories will be writable by anyone who can access that port (9418) as +that transport is unauthenticated. + +Reference Discovery +------------------- + +The reference discovery phase is done nearly the same way as it is in the +fetching protocol. Each reference obj-id and name on the server is sent +in packet-line format to the client, followed by a flush-pkt. The only +real difference is that the capability listing is different - the only +possible values are 'report-status', 'delete-refs' and 'ofs-delta'. + +Reference Update Request and Packfile Transfer +---------------------------------------------- + +Once the client knows what references the server is at, it can send a +list of reference update requests. For each reference on the server +that it wants to update, it sends a line listing the obj-id currently on +the server, the obj-id the client would like to update it to and the name +of the reference. + +This list is followed by a flush-pkt and then the packfile that should +contain all the objects that the server will need to complete the new +references. + +---- + update-request = *shallow ( command-list | push-cert ) [packfile] + + shallow = PKT-LINE("shallow" SP obj-id LF) + + command-list = PKT-LINE(command NUL capability-list LF) + *PKT-LINE(command LF) + flush-pkt + + command = create / delete / update + create = zero-id SP new-id SP name + delete = old-id SP zero-id SP name + update = old-id SP new-id SP name + + old-id = obj-id + new-id = obj-id + + push-cert = PKT-LINE("push-cert" NUL capability-list LF) + PKT-LINE("certificate version 0.1" LF) + PKT-LINE("pusher" SP ident LF) + PKT-LINE("pushee" SP url LF) + PKT-LINE("nonce" SP nonce LF) + PKT-LINE(LF) + *PKT-LINE(command LF) + *PKT-LINE(gpg-signature-lines LF) + PKT-LINE("push-cert-end" LF) + + packfile = "PACK" 28*(OCTET) +---- + +If the receiving end does not support delete-refs, the sending end MUST +NOT ask for delete command. + +If the receiving end does not support push-cert, the sending end +MUST NOT send a push-cert command. When a push-cert command is +sent, command-list MUST NOT be sent; the commands recorded in the +push certificate is used instead. + +The packfile MUST NOT be sent if the only command used is 'delete'. + +A packfile MUST be sent if either create or update command is used, +even if the server already has all the necessary objects. In this +case the client MUST send an empty packfile. The only time this +is likely to happen is if the client is creating +a new branch or a tag that points to an existing obj-id. + +The server will receive the packfile, unpack it, then validate each +reference that is being updated that it hasn't changed while the request +was being processed (the obj-id is still the same as the old-id), and +it will run any update hooks to make sure that the update is acceptable. +If all of that is fine, the server will then update the references. + +Push Certificate +---------------- + +A push certificate begins with a set of header lines. After the +header and an empty line, the protocol commands follow, one per +line. + +Currently, the following header fields are defined: + +`pusher` ident:: + Identify the GPG key in "Human Readable Name <email@address>" + format. + +`pushee` url:: + The repository URL (anonymized, if the URL contains + authentication material) the user who ran `git push` + intended to push into. + +`nonce` nonce:: + The 'nonce' string the receiving repository asked the + pushing user to include in the certificate, to prevent + replay attacks. + +The GPG signature lines are a detached signature for the contents +recorded in the push certificate before the signature block begins. +The detached signature is used to certify that the commands were +given by the pusher, who must be the signer. + +Report Status +------------- + +After receiving the pack data from the sender, the receiver sends a +report if 'report-status' capability is in effect. +It is a short listing of what happened in that update. It will first +list the status of the packfile unpacking as either 'unpack ok' or +'unpack [error]'. Then it will list the status for each of the references +that it tried to update. Each line is either 'ok [refname]' if the +update was successful, or 'ng [refname] [error]' if the update was not. + +---- + report-status = unpack-status + 1*(command-status) + flush-pkt + + unpack-status = PKT-LINE("unpack" SP unpack-result LF) + unpack-result = "ok" / error-msg + + command-status = command-ok / command-fail + command-ok = PKT-LINE("ok" SP refname LF) + command-fail = PKT-LINE("ng" SP refname SP error-msg LF) + + error-msg = 1*(OCTECT) ; where not "ok" +---- + +Updates can be unsuccessful for a number of reasons. The reference can have +changed since the reference discovery phase was originally sent, meaning +someone pushed in the meantime. The reference being pushed could be a +non-fast-forward reference and the update hooks or configuration could be +set to not allow that, etc. Also, some references can be updated while others +can be rejected. + +An example client/server communication might look like this: + +---- + S: 007c74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/local\0report-status delete-refs ofs-delta\n + S: 003e7d1665144a3a975c05f1f43902ddaf084e784dbe refs/heads/debug\n + S: 003f74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/master\n + S: 003f74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/team\n + S: 0000 + + C: 003e7d1665144a3a975c05f1f43902ddaf084e784dbe 74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/debug\n + C: 003e74730d410fcb6603ace96f1dc55ea6196122532d 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a refs/heads/master\n + C: 0000 + C: [PACKDATA] + + S: 000eunpack ok\n + S: 0018ok refs/heads/debug\n + S: 002ang refs/heads/master non-fast-forward\n +---- diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt new file mode 100644 index 0000000000..eaab6b4ac7 --- /dev/null +++ b/Documentation/technical/protocol-capabilities.txt @@ -0,0 +1,277 @@ +Git Protocol Capabilities +========================= + +Servers SHOULD support all capabilities defined in this document. + +On the very first line of the initial server response of either +receive-pack and upload-pack the first reference is followed by +a NUL byte and then a list of space delimited server capabilities. +These allow the server to declare what it can and cannot support +to the client. + +Client will then send a space separated list of capabilities it wants +to be in effect. The client MUST NOT ask for capabilities the server +did not say it supports. + +Server MUST diagnose and abort if capabilities it does not understand +was sent. Server MUST NOT ignore capabilities that client requested +and server advertised. As a consequence of these rules, server MUST +NOT advertise capabilities it does not understand. + +The 'atomic', 'report-status', 'delete-refs', 'quiet', and 'push-cert' +capabilities are sent and recognized by the receive-pack (push to server) +process. + +The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized +by both upload-pack and receive-pack protocols. The 'agent' capability +may optionally be sent in both protocols. + +All other capabilities are only recognized by the upload-pack (fetch +from server) process. + +multi_ack +--------- + +The 'multi_ack' capability allows the server to return "ACK obj-id +continue" as soon as it finds a commit that it can use as a common +base, between the client's wants and the client's have set. + +By sending this early, the server can potentially head off the client +from walking any further down that particular branch of the client's +repository history. The client may still need to walk down other +branches, sending have lines for those, until the server has a +complete cut across the DAG, or the client has said "done". + +Without multi_ack, a client sends have lines in --date-order until +the server has found a common base. That means the client will send +have lines that are already known by the server to be common, because +they overlap in time with another branch that the server hasn't found +a common base on yet. + +For example suppose the client has commits in caps that the server +doesn't and the server has commits in lower case that the client +doesn't, as in the following diagram: + + +---- u ---------------------- x + / +----- y + / / + a -- b -- c -- d -- E -- F + \ + +--- Q -- R -- S + +If the client wants x,y and starts out by saying have F,S, the server +doesn't know what F,S is. Eventually the client says "have d" and +the server sends "ACK d continue" to let the client know to stop +walking down that line (so don't send c-b-a), but it's not done yet, +it needs a base for x. The client keeps going with S-R-Q, until a +gets reached, at which point the server has a clear base and it all +ends. + +Without multi_ack the client would have sent that c-b-a chain anyway, +interleaved with S-R-Q. + +multi_ack_detailed +------------------ +This is an extension of multi_ack that permits client to better +understand the server's in-memory state. See pack-protocol.txt, +section "Packfile Negotiation" for more information. + +no-done +------- +This capability should only be used with the smart HTTP protocol. If +multi_ack_detailed and no-done are both present, then the sender is +free to immediately send a pack following its first "ACK obj-id ready" +message. + +Without no-done in the smart HTTP protocol, the server session would +end and the client has to make another trip to send "done" before +the server can send the pack. no-done removes the last round and +thus slightly reduces latency. + +thin-pack +--------- + +A thin pack is one with deltas which reference base objects not +contained within the pack (but are known to exist at the receiving +end). This can reduce the network traffic significantly, but it +requires the receiving end to know how to "thicken" these packs by +adding the missing bases to the pack. + +The upload-pack server advertises 'thin-pack' when it can generate +and send a thin pack. A client requests the 'thin-pack' capability +when it understands how to "thicken" it, notifying the server that +it can receive such a pack. A client MUST NOT request the +'thin-pack' capability if it cannot turn a thin pack into a +self-contained pack. + +Receive-pack, on the other hand, is assumed by default to be able to +handle thin packs, but can ask the client not to use the feature by +advertising the 'no-thin' capability. A client MUST NOT send a thin +pack if the server advertises the 'no-thin' capability. + +The reasons for this asymmetry are historical. The receive-pack +program did not exist until after the invention of thin packs, so +historically the reference implementation of receive-pack always +understood thin packs. Adding 'no-thin' later allowed receive-pack +to disable the feature in a backwards-compatible manner. + + +side-band, side-band-64k +------------------------ + +This capability means that server can send, and client understand multiplexed +progress reports and error info interleaved with the packfile itself. + +These two options are mutually exclusive. A modern client always +favors 'side-band-64k'. + +Either mode indicates that the packfile data will be streamed broken +up into packets of up to either 1000 bytes in the case of 'side_band', +or 65520 bytes in the case of 'side_band_64k'. Each packet is made up +of a leading 4-byte pkt-line length of how much data is in the packet, +followed by a 1-byte stream code, followed by the actual data. + +The stream code can be one of: + + 1 - pack data + 2 - progress messages + 3 - fatal error message just before stream aborts + +The "side-band-64k" capability came about as a way for newer clients +that can handle much larger packets to request packets that are +actually crammed nearly full, while maintaining backward compatibility +for the older clients. + +Further, with side-band and its up to 1000-byte messages, it's actually +999 bytes of payload and 1 byte for the stream code. With side-band-64k, +same deal, you have up to 65519 bytes of data and 1 byte for the stream +code. + +The client MUST send only maximum of one of "side-band" and "side- +band-64k". Server MUST diagnose it as an error if client requests +both. + +ofs-delta +--------- + +Server can send, and client understand PACKv2 with delta referring to +its base by position in pack rather than by an obj-id. That is, they can +send/read OBJ_OFS_DELTA (aka type 6) in a packfile. + +agent +----- + +The server may optionally send a capability of the form `agent=X` to +notify the client that the server is running version `X`. The client may +optionally return its own agent string by responding with an `agent=Y` +capability (but it MUST NOT do so if the server did not mention the +agent capability). The `X` and `Y` strings may contain any printable +ASCII characters except space (i.e., the byte range 32 < x < 127), and +are typically of the form "package/version" (e.g., "git/1.8.3.1"). The +agent strings are purely informative for statistics and debugging +purposes, and MUST NOT be used to programmatically assume the presence +or absence of particular features. + +shallow +------- + +This capability adds "deepen", "shallow" and "unshallow" commands to +the fetch-pack/upload-pack protocol so clients can request shallow +clones. + +no-progress +----------- + +The client was started with "git clone -q" or something, and doesn't +want that side band 2. Basically the client just says "I do not +wish to receive stream 2 on sideband, so do not send it to me, and if +you did, I will drop it on the floor anyway". However, the sideband +channel 3 is still used for error responses. + +include-tag +----------- + +The 'include-tag' capability is about sending annotated tags if we are +sending objects they point to. If we pack an object to the client, and +a tag object points exactly at that object, we pack the tag object too. +In general this allows a client to get all new annotated tags when it +fetches a branch, in a single network connection. + +Clients MAY always send include-tag, hardcoding it into a request when +the server advertises this capability. The decision for a client to +request include-tag only has to do with the client's desires for tag +data, whether or not a server had advertised objects in the +refs/tags/* namespace. + +Servers MUST pack the tags if their referrant is packed and the client +has requested include-tags. + +Clients MUST be prepared for the case where a server has ignored +include-tag and has not actually sent tags in the pack. In such +cases the client SHOULD issue a subsequent fetch to acquire the tags +that include-tag would have otherwise given the client. + +The server SHOULD send include-tag, if it supports it, regardless +of whether or not there are tags available. + +report-status +------------- + +The receive-pack process can receive a 'report-status' capability, +which tells it that the client wants a report of what happened after +a packfile upload and reference update. If the pushing client requests +this capability, after unpacking and updating references the server +will respond with whether the packfile unpacked successfully and if +each reference was updated successfully. If any of those were not +successful, it will send back an error message. See pack-protocol.txt +for example messages. + +delete-refs +----------- + +If the server sends back the 'delete-refs' capability, it means that +it is capable of accepting a zero-id value as the target +value of a reference update. It is not sent back by the client, it +simply informs the client that it can be sent zero-id values +to delete references. + +quiet +----- + +If the receive-pack server advertises the 'quiet' capability, it is +capable of silencing human-readable progress output which otherwise may +be shown when processing the received pack. A send-pack client should +respond with the 'quiet' capability to suppress server-side progress +reporting if the local progress reporting is also being suppressed +(e.g., via `push -q`, or if stderr does not go to a tty). + +atomic +------ + +If the server sends the 'atomic' capability it is capable of accepting +atomic pushes. If the pushing client requests this capability, the server +will update the refs in one atomic transaction. Either all refs are +updated or none. + +allow-tip-sha1-in-want +---------------------- + +If the upload-pack server advertises this capability, fetch-pack may +send "want" lines with SHA-1s that exist at the server but are not +advertised by upload-pack. + +allow-reachable-sha1-in-want +---------------------------- + +If the upload-pack server advertises this capability, fetch-pack may +send "want" lines with SHA-1s that exist at the server but are not +advertised by upload-pack. + +push-cert=<nonce> +----------------- + +The receive-pack server that advertises this capability is willing +to accept a signed push certificate, and asks the <nonce> to be +included in the push certificate. A send-pack client MUST NOT +send a push-cert packet unless the receive-pack server advertises +this capability. diff --git a/Documentation/technical/protocol-common.txt b/Documentation/technical/protocol-common.txt new file mode 100644 index 0000000000..889985f707 --- /dev/null +++ b/Documentation/technical/protocol-common.txt @@ -0,0 +1,96 @@ +Documentation Common to Pack and Http Protocols +=============================================== + +ABNF Notation +------------- + +ABNF notation as described by RFC 5234 is used within the protocol documents, +except the following replacement core rules are used: +---- + HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" +---- + +We also define the following common rules: +---- + NUL = %x00 + zero-id = 40*"0" + obj-id = 40*(HEXDIGIT) + + refname = "HEAD" + refname /= "refs/" <see discussion below> +---- + +A refname is a hierarchical octet string beginning with "refs/" and +not violating the 'git-check-ref-format' command's validation rules. +More specifically, they: + +. They can include slash `/` for hierarchical (directory) + grouping, but no slash-separated component can begin with a + dot `.`. + +. They must contain at least one `/`. This enforces the presence of a + category like `heads/`, `tags/` etc. but the actual names are not + restricted. + +. They cannot have two consecutive dots `..` anywhere. + +. They cannot have ASCII control characters (i.e. bytes whose + values are lower than \040, or \177 `DEL`), space, tilde `~`, + caret `^`, colon `:`, question-mark `?`, asterisk `*`, + or open bracket `[` anywhere. + +. They cannot end with a slash `/` or a dot `.`. + +. They cannot end with the sequence `.lock`. + +. They cannot contain a sequence `@{`. + +. They cannot contain a `\\`. + + +pkt-line Format +--------------- + +Much (but not all) of the payload is described around pkt-lines. + +A pkt-line is a variable length binary string. The first four bytes +of the line, the pkt-len, indicates the total length of the line, +in hexadecimal. The pkt-len includes the 4 bytes used to contain +the length's hexadecimal representation. + +A pkt-line MAY contain binary data, so implementors MUST ensure +pkt-line parsing/formatting routines are 8-bit clean. + +A non-binary line SHOULD BE terminated by an LF, which if present +MUST be included in the total length. + +The maximum length of a pkt-line's data component is 65520 bytes. +Implementations MUST NOT send pkt-line whose length exceeds 65524 +(65520 bytes of payload + 4 bytes of length data). + +Implementations SHOULD NOT send an empty pkt-line ("0004"). + +A pkt-line with a length field of 0 ("0000"), called a flush-pkt, +is a special case and MUST be handled differently than an empty +pkt-line ("0004"). + +---- + pkt-line = data-pkt / flush-pkt + + data-pkt = pkt-len pkt-payload + pkt-len = 4*(HEXDIG) + pkt-payload = (pkt-len - 4)*(OCTET) + + flush-pkt = "0000" +---- + +Examples (as C-style strings): + +---- + pkt-line actual value + --------------------------------- + "0006a\n" "a\n" + "0005a" "a" + "000bfoobar\n" "foobar\n" + "0004" "" +---- diff --git a/Documentation/technical/racy-git.txt b/Documentation/technical/racy-git.txt index 5030d9f2f8..4a8be4d144 100644 --- a/Documentation/technical/racy-git.txt +++ b/Documentation/technical/racy-git.txt @@ -1,21 +1,21 @@ -Use of index and Racy git problem +Use of index and Racy Git problem ================================= Background ---------- -The index is one of the most important data structures in git. +The index is one of the most important data structures in Git. It represents a virtual working tree state by recording list of paths and their object names and serves as a staging area to write out the next tree object to be committed. The state is "virtual" in the sense that it does not necessarily have to, and often does not, match the files in the working tree. -There are cases git needs to examine the differences between the +There are cases Git needs to examine the differences between the virtual working tree state in the index and the files in the working tree. The most obvious case is when the user asks `git diff` (or its low level implementation, `git diff-files`) or -`git-ls-files --modified`. In addition, git internally checks +`git-ls-files --modified`. In addition, Git internally checks if the files in the working tree are different from what are recorded in the index to avoid stomping on local changes in them during patch application, switching branches, and merging. @@ -24,16 +24,16 @@ In order to speed up this comparison between the files in the working tree and the index entries, the index entries record the information obtained from the filesystem via `lstat(2)` system call when they were last updated. When checking if they differ, -git first runs `lstat(2)` on the files and compares the result +Git first runs `lstat(2)` on the files and compares the result with this information (this is what was originally done by the `ce_match_stat()` function, but the current code does it in `ce_match_stat_basic()` function). If some of these "cached -stat information" fields do not match, git can tell that the +stat information" fields do not match, Git can tell that the files are modified without even looking at their contents. Note: not all members in `struct stat` obtained via `lstat(2)` are used for this comparison. For example, `st_atime` obviously -is not useful. Currently, git compares the file type (regular +is not useful. Currently, Git compares the file type (regular files vs symbolic links) and executable bits (only for regular files) from `st_mode` member, `st_mtime` and `st_ctime` timestamps, `st_uid`, `st_gid`, `st_ino`, and `st_size` members. @@ -41,13 +41,19 @@ With a `USE_STDEV` compile-time option, `st_dev` is also compared, but this is not enabled by default because this member is not stable on network filesystems. With `USE_NSEC` compile-time option, `st_mtim.tv_nsec` and `st_ctim.tv_nsec` -members are also compared, but this is not enabled by default -because the value of this member becomes meaningless once the -inode is evicted from the inode cache on filesystems that do not -store it on disk. - - -Racy git +members are also compared. On Linux, this is not enabled by default +because in-core timestamps can have finer granularity than +on-disk timestamps, resulting in meaningless changes when an +inode is evicted from the inode cache. See commit 8ce13b0 +of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git +([PATCH] Sync in core time granularity with filesystems, +2005-01-04). This patch is included in kernel 2.6.11 and newer, but +only fixes the issue for file systems with exactly 1 ns or 1 s +resolution. Other file systems are still broken in current Linux +kernels (e.g. CEPH, CIFS, NTFS, UDF), see +https://lkml.org/lkml/2015/6/9/714 + +Racy Git -------- There is one slight problem with the optimization based on the @@ -65,13 +71,13 @@ timestamp does not change, after this sequence, the cached stat information the index entry records still exactly match what you would see in the filesystem, even though the file `foo` is now different. -This way, git can incorrectly think files in the working tree +This way, Git can incorrectly think files in the working tree are unmodified even though they actually are. This is called -the "racy git" problem (discovered by Pasky), and the entries +the "racy Git" problem (discovered by Pasky), and the entries that appear clean when they may not be because of this problem are called "racily clean". -To avoid this problem, git does two things: +To avoid this problem, Git does two things: . When the cached stat information says the file has not been modified, and the `st_mtime` is the same as (or newer than) @@ -114,7 +120,7 @@ timestamp comparison check done with the former logic anymore. The latter makes sure that the cached stat information for `foo` would never match with the file in the working tree, so later checks by `ce_match_stat_basic()` would report that the index entry -does not match the file and git does not have to fall back on more +does not match the file and Git does not have to fall back on more expensive `ce_modified_check_fs()`. @@ -133,9 +139,9 @@ them, and give the same timestamp to the index file: $ git ls-files | git update-index --stdin $ touch -r .datestamp .git/index -This will make all index entries racily clean. The linux-2.6 -project, for example, there are over 20,000 files in the working -tree. On my Athron 64X2 3800+, after the above: +This will make all index entries racily clean. The linux project, for +example, there are over 20,000 files in the working tree. On my +Athlon 64 X2 3800+, after the above: $ /usr/bin/time git diff-files 1.68user 0.54system 0:02.22elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k @@ -157,7 +163,7 @@ of the cached stat information. Avoiding runtime penalty ------------------------ -In order to avoid the above runtime penalty, post 1.4.2 git used +In order to avoid the above runtime penalty, post 1.4.2 Git used to have a code that made sure the index file got timestamp newer than the youngest files in the index when there are many young files with the same timestamp as the @@ -184,7 +190,7 @@ In a large project where raciness avoidance cost really matters, however, the initial computation of all object names in the index takes more than one second, and the index file is written out after all that happens. Therefore the timestamp of the -index file will be more than one seconds later than the the +index file will be more than one seconds later than the youngest file in the working tree. This means that in these cases there actually will not be any racily clean entry in the resulting index. diff --git a/Documentation/technical/send-pack-pipeline.txt b/Documentation/technical/send-pack-pipeline.txt index 681efe4219..9b5a0bc186 100644 --- a/Documentation/technical/send-pack-pipeline.txt +++ b/Documentation/technical/send-pack-pipeline.txt @@ -1,5 +1,5 @@ -git-send-pack -============= +Git-send-pack internals +======================= Overall operation ----------------- diff --git a/Documentation/technical/shallow.txt b/Documentation/technical/shallow.txt index 559263af48..5183b15422 100644 --- a/Documentation/technical/shallow.txt +++ b/Documentation/technical/shallow.txt @@ -1,8 +1,14 @@ -Def.: Shallow commits do have parents, but not in the shallow +Shallow commits +=============== + +.Definition +********************************************************* +Shallow commits do have parents, but not in the shallow repo, and therefore grafts are introduced pretending that these commits have no parents. +********************************************************* -The basic idea is to write the SHA1s of shallow commits into +The basic idea is to write the SHA-1s of shallow commits into $GIT_DIR/shallow, and handle its contents like the contents of $GIT_DIR/info/grafts (with the difference that shallow cannot contain parent information). @@ -12,7 +18,7 @@ even the config, since the user should not touch that file at all (even throughout development of the shallow clone, it was never manually edited!). -Each line contains exactly one SHA1. When read, a commit_graft +Each line contains exactly one SHA-1. When read, a commit_graft will be constructed, which has nr_parent < 0 to make it easier to discern from user provided grafts. @@ -47,3 +53,6 @@ It also writes an appropriate $GIT_DIR/shallow. You can deepen a shallow repository with "git-fetch --depth 20 repo branch", which will fetch branch from repo, but stop at depth 20, updating $GIT_DIR/shallow. + +The special depth 2147483647 (or 0x7fffffff, the largest positive +number a signed 32-bit integer can contain) means infinite depth. diff --git a/Documentation/technical/trivial-merge.txt b/Documentation/technical/trivial-merge.txt index 24c84100b0..c79d4a7c47 100644 --- a/Documentation/technical/trivial-merge.txt +++ b/Documentation/technical/trivial-merge.txt @@ -74,24 +74,24 @@ For multiple ancestors, a '+' means that this case applies even if only one ancestor or remote fits; a '^' means all of the ancestors must be the same. -case ancest head remote result ----------------------------------------- -1 (empty)+ (empty) (empty) (empty) -2ALT (empty)+ *empty* remote remote -2 (empty)^ (empty) remote no merge -3ALT (empty)+ head *empty* head -3 (empty)^ head (empty) no merge -4 (empty)^ head remote no merge -5ALT * head head head -6 ancest+ (empty) (empty) no merge -8 ancest^ (empty) ancest no merge -7 ancest+ (empty) remote no merge -10 ancest^ ancest (empty) no merge -9 ancest+ head (empty) no merge -16 anc1/anc2 anc1 anc2 no merge -13 ancest+ head ancest head -14 ancest+ ancest remote remote -11 ancest+ head remote no merge + case ancest head remote result + ---------------------------------------- + 1 (empty)+ (empty) (empty) (empty) + 2ALT (empty)+ *empty* remote remote + 2 (empty)^ (empty) remote no merge + 3ALT (empty)+ head *empty* head + 3 (empty)^ head (empty) no merge + 4 (empty)^ head remote no merge + 5ALT * head head head + 6 ancest+ (empty) (empty) no merge + 8 ancest^ (empty) ancest no merge + 7 ancest+ (empty) remote no merge + 10 ancest^ ancest (empty) no merge + 9 ancest+ head (empty) no merge + 16 anc1/anc2 anc1 anc2 no merge + 13 ancest+ head ancest head + 14 ancest+ ancest remote remote + 11 ancest+ head remote no merge Only #2ALT and #3ALT use *empty*, because these are the only cases where there can be conflicts that didn't exist before. Note that we |