diff options
Diffstat (limited to 'Documentation/technical')
| -rw-r--r-- | Documentation/technical/api-argv-array.txt | 10 | ||||
| -rw-r--r-- | Documentation/technical/api-config.txt | 7 | ||||
| -rw-r--r-- | Documentation/technical/api-credentials.txt | 4 | ||||
| -rw-r--r-- | Documentation/technical/api-lockfile.txt | 220 | ||||
| -rw-r--r-- | Documentation/technical/api-parse-options.txt | 34 | ||||
| -rw-r--r-- | Documentation/technical/api-remote.txt | 4 | ||||
| -rw-r--r-- | Documentation/technical/api-run-command.txt | 7 | ||||
| -rw-r--r-- | Documentation/technical/api-submodule-config.txt | 62 | ||||
| -rw-r--r-- | Documentation/technical/api-trace.txt | 45 | ||||
| -rw-r--r-- | Documentation/technical/index-format.txt | 2 | ||||
| -rw-r--r-- | Documentation/technical/pack-protocol.txt | 46 | ||||
| -rw-r--r-- | Documentation/technical/protocol-common.txt | 5 | ||||
| -rw-r--r-- | Documentation/technical/repository-version.txt | 88 |
13 files changed, 280 insertions, 254 deletions
diff --git a/Documentation/technical/api-argv-array.txt b/Documentation/technical/api-argv-array.txt index 1a797812fb..cfc063018c 100644 --- a/Documentation/technical/api-argv-array.txt +++ b/Documentation/technical/api-argv-array.txt @@ -46,6 +46,9 @@ Functions 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_pushv`:: + Push a null-terminated array of strings onto the end of the array. + `argv_array_pop`:: Remove the final element from the array. If there are no elements in the array, do nothing. @@ -53,3 +56,10 @@ Functions `argv_array_clear`:: Free all memory associated with the array and return it to the initial, empty state. + +`argv_array_detach`:: + Disconnect the `argv` member from the `argv_array` struct and + return it. The caller is responsible for freeing the memory used + by the array, and by the strings it references. After detaching, + the `argv_array` is in a reinitialized state and can be pushed + into again. diff --git a/Documentation/technical/api-config.txt b/Documentation/technical/api-config.txt index 0d8b99b368..20741f345e 100644 --- a/Documentation/technical/api-config.txt +++ b/Documentation/technical/api-config.txt @@ -63,13 +63,6 @@ parse for configuration, rather than looking in the usual files. Regular 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 ---------------------- diff --git a/Documentation/technical/api-credentials.txt b/Documentation/technical/api-credentials.txt index e44426dd04..75368f26ca 100644 --- a/Documentation/technical/api-credentials.txt +++ b/Documentation/technical/api-credentials.txt @@ -243,7 +243,7 @@ appended to its command line, which is one of: 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). +FORMAT` in linkgit:git-credential[1] 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 @@ -268,4 +268,4 @@ See also linkgit:gitcredentials[7] -linkgit:git-config[5] (See configuration variables `credential.*`) +linkgit:git-config[1] (See configuration variables `credential.*`) diff --git a/Documentation/technical/api-lockfile.txt b/Documentation/technical/api-lockfile.txt deleted file mode 100644 index 93b5f23e4c..0000000000 --- a/Documentation/technical/api-lockfile.txt +++ /dev/null @@ -1,220 +0,0 @@ -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-parse-options.txt b/Documentation/technical/api-parse-options.txt index 1f2db31312..27bd701c0d 100644 --- a/Documentation/technical/api-parse-options.txt +++ b/Documentation/technical/api-parse-options.txt @@ -144,8 +144,12 @@ There are some macros to easily define options: `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`. + Each use of `--option` increments `int_var`, starting from zero + (even if initially negative), and `--no-option` resets it to + zero. To determine if `--option` or `--no-option` was encountered at + all, initialize `int_var` to a negative value, and if it is still + negative after parse_options(), then neither `--option` nor + `--no-option` was seen. `OPT_BIT(short, long, &int_var, description, mask)`:: Introduce a boolean option. @@ -168,6 +172,12 @@ There are some macros to easily define options: Introduce an option with integer argument. The integer is put into `int_var`. +`OPT_MAGNITUDE(short, long, &unsigned_long_var, description)`:: + Introduce an option with a size argument. The argument must be a + non-negative integer and may include a suffix of 'k', 'm' or 'g' to + scale the provided value by 1024, 1024^2 or 1024^3 respectively. + The scaled value is put into `unsigned_long_var`. + `OPT_DATE(short, long, &int_var, description)`:: Introduce an option with date argument, see `approxidate()`. The timestamp is put into `int_var`. @@ -212,6 +222,26 @@ There are some macros to easily define options: Use it to hide deprecated options that are still to be recognized and ignored silently. +`OPT_PASSTHRU(short, long, &char_var, arg_str, description, flags)`:: + Introduce an option that will be reconstructed into a char* string, + which must be initialized to NULL. This is useful when you need to + pass the command-line option to another command. Any previous value + will be overwritten, so this should only be used for options where + the last one specified on the command line wins. + +`OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`:: + Introduce an option where all instances of it on the command-line will + be reconstructed into an argv_array. This is useful when you need to + pass the command-line option, which can be specified multiple times, + to another command. + +`OPT_CMDMODE(short, long, &int_var, description, enum_val)`:: + Define an "operation mode" option, only one of which in the same + group of "operating mode" options that share the same `int_var` + can be given by the user. `enum_val` is set to `int_var` when the + option is used, but an error is reported if other "operating mode" + option has already set its value to the same `int_var`. + The last element of the array must be `OPT_END()`. diff --git a/Documentation/technical/api-remote.txt b/Documentation/technical/api-remote.txt index 2cfdd224a8..f10941b2e8 100644 --- a/Documentation/technical/api-remote.txt +++ b/Documentation/technical/api-remote.txt @@ -51,6 +51,10 @@ struct remote The proxy to use for curl (http, https, ftp, etc.) URLs. +`http_proxy_authmethod`:: + + The method used for authenticating against `http_proxy`. + 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. diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt index a9fdb45b93..8bf3e37f53 100644 --- a/Documentation/technical/api-run-command.txt +++ b/Documentation/technical/api-run-command.txt @@ -46,6 +46,13 @@ Functions The argument dir corresponds the member .dir. The argument env corresponds to the member .env. +`child_process_clear`:: + + Release the memory associated with the struct child_process. + Most users of the run-command API don't need to call this + function explicitly because `start_command` invokes it on + failure and `finish_command` calls it automatically already. + The functions above do the following: . If a system call failed, errno is set and -1 is returned. A diagnostic diff --git a/Documentation/technical/api-submodule-config.txt b/Documentation/technical/api-submodule-config.txt new file mode 100644 index 0000000000..941fa178dd --- /dev/null +++ b/Documentation/technical/api-submodule-config.txt @@ -0,0 +1,62 @@ +submodule config cache API +========================== + +The submodule config cache API allows to read submodule +configurations/information from specified revisions. Internally +information is lazily read into a cache that is used to avoid +unnecessary parsing of the same .gitmodule files. Lookups can be done by +submodule path or name. + +Usage +----- + +To initialize the cache with configurations from the worktree the caller +typically first calls `gitmodules_config()` to read values from the +worktree .gitmodules and then to overlay the local git config values +`parse_submodule_config_option()` from the config parsing +infrastructure. + +The caller can look up information about submodules by using the +`submodule_from_path()` or `submodule_from_name()` functions. They return +a `struct submodule` which contains the values. The API automatically +initializes and allocates the needed infrastructure on-demand. If the +caller does only want to lookup values from revisions the initialization +can be skipped. + +If the internal cache might grow too big or when the caller is done with +the API, all internally cached values can be freed with submodule_free(). + +Data Structures +--------------- + +`struct submodule`:: + + This structure is used to return the information about one + submodule for a certain revision. It is returned by the lookup + functions. + +Functions +--------- + +`void submodule_free()`:: + + Use these to free the internally cached values. + +`int parse_submodule_config_option(const char *var, const char *value)`:: + + Can be passed to the config parsing infrastructure to parse + local (worktree) submodule configurations. + +`const struct submodule *submodule_from_path(const unsigned char *commit_sha1, const char *path)`:: + + Lookup values for one submodule by its commit_sha1 and path. + +`const struct submodule *submodule_from_name(const unsigned char *commit_sha1, const char *name)`:: + + The same as above but lookup by name. + +If given the null_sha1 as commit_sha1 the local configuration of a +submodule will be returned (e.g. consolidated values from local git +configuration and the .gitmodules file in the worktree). + +For an example usage see test-submodule-config.c. diff --git a/Documentation/technical/api-trace.txt b/Documentation/technical/api-trace.txt index 097a651d96..fadb5979c4 100644 --- a/Documentation/technical/api-trace.txt +++ b/Documentation/technical/api-trace.txt @@ -28,7 +28,7 @@ static struct trace_key trace_foo = TRACE_KEY_INIT(FOO); static void trace_print_foo(const char *message) { - trace_print_key(&trace_foo, message); + trace_printf_key(&trace_foo, "%s", message); } ------------ + @@ -95,3 +95,46 @@ for (;;) { } trace_performance(t, "frotz"); ------------ + +Bugs & Caveats +-------------- + +GIT_TRACE_* environment variables can be used to tell Git to show +trace output to its standard error stream. Git can often spawn a pager +internally to run its subcommand and send its standard output and +standard error to it. + +Because GIT_TRACE_PERFORMANCE trace is generated only at the very end +of the program with atexit(), which happens after the pager exits, it +would not work well if you send its log to the standard error output +and let Git spawn the pager at the same time. + +As a work around, you can for example use '--no-pager', or set +GIT_TRACE_PERFORMANCE to another file descriptor which is redirected +to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its +absolute path. + +For example instead of the following command which by default may not +print any performance information: + +------------ +GIT_TRACE_PERFORMANCE=2 git log -1 +------------ + +you may want to use: + +------------ +GIT_TRACE_PERFORMANCE=2 git --no-pager log -1 +------------ + +or: + +------------ +GIT_TRACE_PERFORMANCE=3 3>&2 git log -1 +------------ + +or: + +------------ +GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1 +------------ diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt index 7392ff636c..ade0b0c445 100644 --- a/Documentation/technical/index-format.txt +++ b/Documentation/technical/index-format.txt @@ -170,7 +170,7 @@ Git index format 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 + 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), ... diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt index 4064fc796f..8b36343802 100644 --- a/Documentation/technical/pack-protocol.txt +++ b/Documentation/technical/pack-protocol.txt @@ -14,6 +14,14 @@ 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. +pkt-line Format +--------------- + +The descriptions below build on the pkt-line format described in +protocol-common.txt. When the grammar indicate `PKT-LINE(...)`, unless +otherwise noted the usual pkt-line LF rules apply: the sender SHOULD +include a LF, but the receiver MUST NOT complain if it is not present. + Transports ---------- There are three transports over which the packfile protocol is @@ -143,9 +151,6 @@ with the object name that each reference currently points to. 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. @@ -165,15 +170,15 @@ MUST peel the ref if it's an annotated tag. flush-pkt no-refs = PKT-LINE(zero-id SP "capabilities^{}" - NUL capability-list LF) + NUL capability-list) list-of-refs = first-ref *other-ref first-ref = PKT-LINE(obj-id SP refname - NUL capability-list LF) + NUL capability-list) other-ref = PKT-LINE(other-tip / other-peeled) - other-tip = obj-id SP refname LF - other-peeled = obj-id SP refname "^{}" LF + other-tip = obj-id SP refname + other-peeled = obj-id SP refname "^{}" shallow = PKT-LINE("shallow" SP obj-id) @@ -216,8 +221,8 @@ out of what the server said it could do with the first 'want' line. 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) + first-want = PKT-LINE("want" SP obj-id SP capability-list) + additional-want = PKT-LINE("want" SP obj-id) depth = 1*DIGIT ---- @@ -284,7 +289,7 @@ so that there is always a block of 32 "in-flight on the wire" at a time. compute-end have-list = *have-line - have-line = PKT-LINE("have" SP obj-id LF) + have-line = PKT-LINE("have" SP obj-id) compute-end = flush-pkt / PKT-LINE("done") ---- @@ -348,10 +353,10 @@ 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_multi = PKT-LINE("ACK" SP obj-id ack_status) ack_status = "continue" / "common" / "ready" - ack = PKT-LINE("ACK SP obj-id LF) - nak = PKT-LINE("NAK" LF) + ack = PKT-LINE("ACK" SP obj-id) + nak = PKT-LINE("NAK") ---- A simple clone may look like this (with no 'have' lines): @@ -467,10 +472,10 @@ references. ---- update-request = *shallow ( command-list | push-cert ) [packfile] - shallow = PKT-LINE("shallow" SP obj-id LF) + shallow = PKT-LINE("shallow" SP obj-id) - command-list = PKT-LINE(command NUL capability-list LF) - *PKT-LINE(command LF) + command-list = PKT-LINE(command NUL capability-list) + *PKT-LINE(command) flush-pkt command = create / delete / update @@ -521,7 +526,8 @@ 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. +line. Note that the trailing LF in push-cert PKT-LINEs is _not_ +optional; it must be present. Currently, the following header fields are defined: @@ -560,12 +566,12 @@ update was successful, or 'ng [refname] [error]' if the update was not. 1*(command-status) flush-pkt - unpack-status = PKT-LINE("unpack" SP unpack-result LF) + unpack-status = PKT-LINE("unpack" SP unpack-result) 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) + command-ok = PKT-LINE("ok" SP refname) + command-fail = PKT-LINE("ng" SP refname SP error-msg) error-msg = 1*(OCTECT) ; where not "ok" ---- diff --git a/Documentation/technical/protocol-common.txt b/Documentation/technical/protocol-common.txt index 889985f707..bf30167ae3 100644 --- a/Documentation/technical/protocol-common.txt +++ b/Documentation/technical/protocol-common.txt @@ -62,7 +62,10 @@ 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. +MUST be included in the total length. Receivers MUST treat pkt-lines +with non-binary data the same whether or not they contain the trailing +LF (stripping the LF if present, and not complaining when it is +missing). The maximum length of a pkt-line's data component is 65520 bytes. Implementations MUST NOT send pkt-line whose length exceeds 65524 diff --git a/Documentation/technical/repository-version.txt b/Documentation/technical/repository-version.txt new file mode 100644 index 0000000000..00ad37986e --- /dev/null +++ b/Documentation/technical/repository-version.txt @@ -0,0 +1,88 @@ +Git Repository Format Versions +============================== + +Every git repository is marked with a numeric version in the +`core.repositoryformatversion` key of its `config` file. This version +specifies the rules for operating on the on-disk repository data. An +implementation of git which does not understand a particular version +advertised by an on-disk repository MUST NOT operate on that repository; +doing so risks not only producing wrong results, but actually losing +data. + +Because of this rule, version bumps should be kept to an absolute +minimum. Instead, we generally prefer these strategies: + + - bumping format version numbers of individual data files (e.g., + index, packfiles, etc). This restricts the incompatibilities only to + those files. + + - introducing new data that gracefully degrades when used by older + clients (e.g., pack bitmap files are ignored by older clients, which + simply do not take advantage of the optimization they provide). + +A whole-repository format version bump should only be part of a change +that cannot be independently versioned. For instance, if one were to +change the reachability rules for objects, or the rules for locking +refs, that would require a bump of the repository format version. + +Note that this applies only to accessing the repository's disk contents +directly. An older client which understands only format `0` may still +connect via `git://` to a repository using format `1`, as long as the +server process understands format `1`. + +The preferred strategy for rolling out a version bump (whether whole +repository or for a single file) is to teach git to read the new format, +and allow writing the new format with a config switch or command line +option (for experimentation or for those who do not care about backwards +compatibility with older gits). Then after a long period to allow the +reading capability to become common, we may switch to writing the new +format by default. + +The currently defined format versions are: + +Version `0` +----------- + +This is the format defined by the initial version of git, including but +not limited to the format of the repository directory, the repository +configuration file, and the object and ref storage. Specifying the +complete behavior of git is beyond the scope of this document. + +Version `1` +----------- + +This format is identical to version `0`, with the following exceptions: + + 1. When reading the `core.repositoryformatversion` variable, a git + implementation which supports version 1 MUST also read any + configuration keys found in the `extensions` section of the + configuration file. + + 2. If a version-1 repository specifies any `extensions.*` keys that + the running git has not implemented, the operation MUST NOT + proceed. Similarly, if the value of any known key is not understood + by the implementation, the operation MUST NOT proceed. + +Note that if no extensions are specified in the config file, then +`core.repositoryformatversion` SHOULD be set to `0` (setting it to `1` +provides no benefit, and makes the repository incompatible with older +implementations of git). + +This document will serve as the master list for extensions. Any +implementation wishing to define a new extension should make a note of +it here, in order to claim the name. + +The defined extensions are: + +`noop` +~~~~~~ + +This extension does not change git's behavior at all. It is useful only +for testing format-1 compatibility. + +`preciousObjects` +~~~~~~~~~~~~~~~~~ + +When the config key `extensions.preciousObjects` is set to `true`, +objects in the repository MUST NOT be deleted (e.g., by `git-prune` or +`git repack -d`). |