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-rw-r--r--Documentation/technical/api-argv-array.txt7
-rw-r--r--Documentation/technical/api-config.txt7
-rw-r--r--Documentation/technical/api-credentials.txt4
-rw-r--r--Documentation/technical/api-gitattributes.txt86
-rw-r--r--Documentation/technical/api-hashmap.txt31
-rw-r--r--Documentation/technical/api-in-core-index.txt21
-rw-r--r--Documentation/technical/api-parse-options.txt20
-rw-r--r--Documentation/technical/api-remote.txt4
-rw-r--r--Documentation/technical/api-setup.txt2
-rw-r--r--Documentation/technical/api-sha1-array.txt8
-rw-r--r--Documentation/technical/api-submodule-config.txt14
-rw-r--r--Documentation/technical/api-trace.txt45
-rw-r--r--Documentation/technical/pack-protocol.txt18
-rw-r--r--Documentation/technical/protocol-capabilities.txt34
-rw-r--r--Documentation/technical/protocol-common.txt6
-rw-r--r--Documentation/technical/signature-format.txt186
16 files changed, 410 insertions, 83 deletions
diff --git a/Documentation/technical/api-argv-array.txt b/Documentation/technical/api-argv-array.txt
index 8076172a08..cfc063018c 100644
--- a/Documentation/technical/api-argv-array.txt
+++ b/Documentation/technical/api-argv-array.txt
@@ -56,3 +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-gitattributes.txt b/Documentation/technical/api-gitattributes.txt
index 2602668677..e7cbb7c13a 100644
--- a/Documentation/technical/api-gitattributes.txt
+++ b/Documentation/technical/api-gitattributes.txt
@@ -16,10 +16,15 @@ Data Structure
of no interest to the calling programs. The name of the
attribute can be retrieved by calling `git_attr_name()`.
-`struct git_attr_check`::
+`struct attr_check_item`::
- This structure represents a set of attributes to check in a call
- to `git_check_attr()` function, and receives the results.
+ This structure represents one attribute and its value.
+
+`struct attr_check`::
+
+ This structure represents a collection of `attr_check_item`.
+ It is passed to `git_check_attr()` function, specifying the
+ attributes to check, and receives their values.
Attribute Values
@@ -27,7 +32,7 @@ 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_check_item` records it. There are three macros to check these:
`ATTR_TRUE()`::
@@ -48,49 +53,51 @@ 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.
+* Prepare `struct attr_check` using attr_check_initl()
+ function, enumerating the names of attributes whose values you are
+ interested in, terminated with a NULL pointer. Alternatively, an
+ empty `struct attr_check` can be prepared by calling
+ `attr_check_alloc()` function and then attributes you want to
+ ask about can be added to it with `attr_check_append()`
+ 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.
+* Inspect `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.
+To see how attributes "crlf" and "ident" 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()`:
+. Prepare a `struct attr_check` with two elements (because
+ we are checking two attributes):
------------
-static struct git_attr_check check[2];
+static struct attr_check *check;
static void setup_check(void)
{
- if (check[0].attr)
+ if (check)
return; /* already done */
- check[0].attr = git_attr("crlf");
- check[1].attr = git_attr("ident");
+ check = attr_check_initl("crlf", "ident", NULL);
}
------------
-. Call `git_check_attr()` with the prepared array of `struct git_attr_check`:
+. Call `git_check_attr()` with the prepared `struct attr_check`:
------------
const char *path;
setup_check();
- git_check_attr(path, ARRAY_SIZE(check), check);
+ git_check_attr(path, check);
------------
-. Act on `.value` member of the result, left in `check[]`:
+. Act on `.value` member of the result, left in `check->items[]`:
------------
- const char *value = check[0].value;
+ const char *value = check->items[0].value;
if (ATTR_TRUE(value)) {
The attribute is Set, by listing only the name of the
@@ -109,20 +116,39 @@ static void setup_check(void)
}
------------
+To see how attributes in argv[] are set for different paths, only
+the first step in the above would be different.
+
+------------
+static struct attr_check *check;
+static void setup_check(const char **argv)
+{
+ check = attr_check_alloc();
+ while (*argv) {
+ struct git_attr *attr = git_attr(*argv);
+ attr_check_append(check, attr);
+ argv++;
+ }
+}
+------------
+
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.
+* Prepare an empty `attr_check` structure by calling
+ `attr_check_alloc()`.
+
+* Call `git_all_attrs()`, which populates the `attr_check`
+ with the attributes attached to the path.
-* 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.)
+* Iterate over the `attr_check.items[]` array to examine
+ the attribute names and values. The name of the attribute
+ described by a `attr_check.items[]` object can be retrieved via
+ `git_attr_name(check->items[i].attr)`. (Please note that no items
+ will be returned for unset attributes, so `ATTR_UNSET()` will return
+ false for all returned `attr_check.items[]` objects.)
-* Free the `git_array_check` array.
+* Free the `attr_check` struct by calling `attr_check_free()`.
diff --git a/Documentation/technical/api-hashmap.txt b/Documentation/technical/api-hashmap.txt
index ad7a5bddd2..ccc634bbd7 100644
--- a/Documentation/technical/api-hashmap.txt
+++ b/Documentation/technical/api-hashmap.txt
@@ -21,6 +21,9 @@ that the hashmap is initialized. It may also be useful for statistical purposes
`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.
++
+When `disallow_rehash` is set, automatic rehashes are prevented during inserts
+and deletes.
`struct hashmap_entry`::
@@ -57,6 +60,7 @@ Functions
`unsigned int strihash(const char *buf)`::
`unsigned int memhash(const void *buf, size_t len)`::
`unsigned int memihash(const void *buf, size_t len)`::
+`unsigned int memihash_cont(unsigned int hash_seed, 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).
@@ -65,6 +69,9 @@ Functions
`memihash` operate on arbitrary-length memory.
+
`strihash` and `memihash` are case insensitive versions.
++
+`memihash_cont` is a variant of `memihash` that allows a computation to be
+continued with another chunk of data.
`unsigned int sha1hash(const unsigned char *sha1)`::
@@ -104,6 +111,11 @@ If `free_entries` is true, each hashmap_entry in the map is freed as well
`entry` points to the entry to initialize.
+
`hash` is the hash code of the entry.
++
+The hashmap_entry structure does not hold references to external resources,
+and it is safe to just discard it once you are done with it (i.e. if
+your structure was allocated with xmalloc(), you can just free(3) it,
+and if it is on stack, you can just let it go out of scope).
`void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)`::
@@ -179,11 +191,28 @@ passed to `hashmap_cmp_fn` to decide whether the entry matches the key.
+
Returns the removed entry, or NULL if not found.
+`void hashmap_disallow_rehash(struct hashmap *map, unsigned value)`::
+
+ Disallow/allow automatic rehashing of the hashmap during inserts
+ and deletes.
++
+This is useful if the caller knows that the hashmap will be accessed
+by multiple threads.
++
+The caller is still responsible for any necessary locking; this simply
+prevents unexpected rehashing. The caller is also responsible for properly
+sizing the initial hashmap to ensure good performance.
++
+A call to allow rehashing does not force a rehash; that might happen
+with the next insert or delete.
+
`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.
+ Used to iterate over all entries of a hashmap. Note that it is
+ not safe to add or remove entries to the hashmap while
+ iterating.
+
`hashmap_iter_init` initializes a `hashmap_iter` structure.
+
diff --git a/Documentation/technical/api-in-core-index.txt b/Documentation/technical/api-in-core-index.txt
deleted file mode 100644
index adbdbf5d75..0000000000
--- a/Documentation/technical/api-in-core-index.txt
+++ /dev/null
@@ -1,21 +0,0 @@
-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-parse-options.txt b/Documentation/technical/api-parse-options.txt
index 5f0757dcc9..36768b479e 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.
@@ -164,6 +168,11 @@ There are some macros to easily define options:
Introduce an option with string argument.
The string argument is put into `str_var`.
+`OPT_STRING_LIST(short, long, &struct string_list, arg_str, description)`::
+ Introduce an option with string argument.
+ The string argument is stored as an element in `string_list`.
+ Use of `--no-option` will clear the list of preceding values.
+
`OPT_INTEGER(short, long, &int_var, description)`::
Introduce an option with integer argument.
The integer is put into `int_var`.
@@ -231,6 +240,13 @@ There are some macros to easily define options:
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-setup.txt b/Documentation/technical/api-setup.txt
index 540e455689..eb1fa9853e 100644
--- a/Documentation/technical/api-setup.txt
+++ b/Documentation/technical/api-setup.txt
@@ -27,8 +27,6 @@ parse_pathspec(). This function takes several arguments:
- 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
diff --git a/Documentation/technical/api-sha1-array.txt b/Documentation/technical/api-sha1-array.txt
index 3e75497a37..dcc52943a5 100644
--- a/Documentation/technical/api-sha1-array.txt
+++ b/Documentation/technical/api-sha1-array.txt
@@ -38,16 +38,20 @@ Functions
`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.
+ not sorted, this function has the side effect of sorting it. If
+ the callback returns a non-zero value, the iteration ends
+ immediately and the callback's return is propagated; otherwise,
+ 0 is returned.
Examples
--------
-----------------------------------------
-void print_callback(const unsigned char sha1[20],
+int print_callback(const unsigned char sha1[20],
void *data)
{
printf("%s\n", sha1_to_hex(sha1));
+ return 0; /* always continue */
}
void some_func(void)
diff --git a/Documentation/technical/api-submodule-config.txt b/Documentation/technical/api-submodule-config.txt
index 941fa178dd..3dce003fda 100644
--- a/Documentation/technical/api-submodule-config.txt
+++ b/Documentation/technical/api-submodule-config.txt
@@ -47,16 +47,20 @@ Functions
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)`::
+`const struct submodule *submodule_from_path(const unsigned char *treeish_name, const char *path)`::
- Lookup values for one submodule by its commit_sha1 and path.
+ Given a tree-ish in the superproject and a path, return the
+ submodule that is bound at the path in the named tree.
-`const struct submodule *submodule_from_name(const unsigned char *commit_sha1, const char *name)`::
+`const struct submodule *submodule_from_name(const unsigned char *treeish_name, 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
+Whenever a submodule configuration is parsed in `parse_submodule_config_option`
+via e.g. `gitmodules_config()`, it will overwrite the null_sha1 entry.
+So in the normal case, when HEAD:.gitmodules is parsed first and then overlayed
+with the repository configuration, the null_sha1 entry contains the local
+configuration of a submodule (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/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index c6977bbc5a..c59ac9936a 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -219,7 +219,9 @@ out of what the server said it could do with the first 'want' line.
shallow-line = PKT-LINE("shallow" SP obj-id)
- depth-request = PKT-LINE("deepen" SP depth)
+ depth-request = PKT-LINE("deepen" SP depth) /
+ PKT-LINE("deepen-since" SP timestamp) /
+ PKT-LINE("deepen-not" SP ref)
first-want = PKT-LINE("want" SP obj-id SP capability-list)
additional-want = PKT-LINE("want" SP obj-id)
@@ -307,7 +309,7 @@ In multi_ack mode:
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
+ * the server will then send a 'NAK' and then wait for another response
from the client - either a 'done' or another list of 'have' lines.
In multi_ack_detailed mode:
@@ -454,7 +456,8 @@ 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'.
+possible values are 'report-status', 'delete-refs', 'ofs-delta' and
+'push-options'.
Reference Update Request and Packfile Transfer
----------------------------------------------
@@ -465,9 +468,10 @@ 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.
+This list is followed by a flush-pkt. Then the push options are transmitted
+one per packet followed by another flush-pkt. After that the packfile that
+should contain all the objects that the server will need to complete the new
+references will be sent.
----
update-request = *shallow ( command-list | push-cert ) [packfile]
@@ -526,7 +530,7 @@ 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. Note that the the trailing LF in push-cert PKT-LINEs is _not_
+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:
diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index eaab6b4ac7..26dcc6f502 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -179,6 +179,31 @@ This capability adds "deepen", "shallow" and "unshallow" commands to
the fetch-pack/upload-pack protocol so clients can request shallow
clones.
+deepen-since
+------------
+
+This capability adds "deepen-since" command to fetch-pack/upload-pack
+protocol so the client can request shallow clones that are cut at a
+specific time, instead of depth. Internally it's equivalent of doing
+"rev-list --max-age=<timestamp>" on the server side. "deepen-since"
+cannot be used with "deepen".
+
+deepen-not
+----------
+
+This capability adds "deepen-not" command to fetch-pack/upload-pack
+protocol so the client can request shallow clones that are cut at a
+specific revision, instead of depth. Internally it's equivalent of
+doing "rev-list --not <rev>" on the server side. "deepen-not"
+cannot be used with "deepen", but can be used with "deepen-since".
+
+deepen-relative
+---------------
+
+If this capability is requested by the client, the semantics of
+"deepen" command is changed. The "depth" argument is the depth from
+the current shallow boundary, instead of the depth from remote refs.
+
no-progress
-----------
@@ -253,6 +278,15 @@ 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.
+push-options
+------------
+
+If the server sends the 'push-options' capability it is able to accept
+push options after the update commands have been sent, but before the
+packfile is streamed. If the pushing client requests this capability,
+the server will pass the options to the pre- and post- receive hooks
+that process this push request.
+
allow-tip-sha1-in-want
----------------------
diff --git a/Documentation/technical/protocol-common.txt b/Documentation/technical/protocol-common.txt
index bf30167ae3..ecedb34bba 100644
--- a/Documentation/technical/protocol-common.txt
+++ b/Documentation/technical/protocol-common.txt
@@ -67,9 +67,9 @@ 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
-(65520 bytes of payload + 4 bytes of length data).
+The maximum length of a pkt-line's data component is 65516 bytes.
+Implementations MUST NOT send pkt-line whose length exceeds 65520
+(65516 bytes of payload + 4 bytes of length data).
Implementations SHOULD NOT send an empty pkt-line ("0004").
diff --git a/Documentation/technical/signature-format.txt b/Documentation/technical/signature-format.txt
new file mode 100644
index 0000000000..2c9406a56a
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+Git signature format
+====================
+
+== Overview
+
+Git uses cryptographic signatures in various places, currently objects (tags,
+commits, mergetags) and transactions (pushes). In every case, the command which
+is about to create an object or transaction determines a payload from that,
+calls gpg to obtain a detached signature for the payload (`gpg -bsa`) and
+embeds the signature into the object or transaction.
+
+Signatures always begin with `-----BEGIN PGP SIGNATURE-----`
+and end with `-----END PGP SIGNATURE-----`, unless gpg is told to
+produce RFC1991 signatures which use `MESSAGE` instead of `SIGNATURE`.
+
+The signed payload and the way the signature is embedded depends
+on the type of the object resp. transaction.
+
+== Tag signatures
+
+- created by: `git tag -s`
+- payload: annotated tag object
+- embedding: append the signature to the unsigned tag object
+- example: tag `signedtag` with subject `signed tag`
+
+----
+object 04b871796dc0420f8e7561a895b52484b701d51a
+type commit
+tag signedtag
+tagger C O Mitter <committer@example.com> 1465981006 +0000
+
+signed tag
+
+signed tag message body
+-----BEGIN PGP SIGNATURE-----
+Version: GnuPG v1
+
+iQEcBAABAgAGBQJXYRhOAAoJEGEJLoW3InGJklkIAIcnhL7RwEb/+QeX9enkXhxn
+rxfdqrvWd1K80sl2TOt8Bg/NYwrUBw/RWJ+sg/hhHp4WtvE1HDGHlkEz3y11Lkuh
+8tSxS3qKTxXUGozyPGuE90sJfExhZlW4knIQ1wt/yWqM+33E9pN4hzPqLwyrdods
+q8FWEqPPUbSJXoMbRPw04S5jrLtZSsUWbRYjmJCHzlhSfFWW4eFd37uquIaLUBS0
+rkC3Jrx7420jkIpgFcTI2s60uhSQLzgcCwdA2ukSYIRnjg/zDkj8+3h/GaROJ72x
+lZyI6HWixKJkWw8lE9aAOD9TmTW9sFJwcVAzmAuFX2kUreDUKMZduGcoRYGpD7E=
+=jpXa
+-----END PGP SIGNATURE-----
+----
+
+- verify with: `git verify-tag [-v]` or `git tag -v`
+
+----
+gpg: Signature made Wed Jun 15 10:56:46 2016 CEST using RSA key ID B7227189
+gpg: Good signature from "Eris Discordia <discord@example.net>"
+gpg: WARNING: This key is not certified with a trusted signature!
+gpg: There is no indication that the signature belongs to the owner.
+Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
+object 04b871796dc0420f8e7561a895b52484b701d51a
+type commit
+tag signedtag
+tagger C O Mitter <committer@example.com> 1465981006 +0000
+
+signed tag
+
+signed tag message body
+----
+
+== Commit signatures
+
+- created by: `git commit -S`
+- payload: commit object
+- embedding: header entry `gpgsig`
+ (content is preceded by a space)
+- example: commit with subject `signed commit`
+
+----
+tree eebfed94e75e7760540d1485c740902590a00332
+parent 04b871796dc0420f8e7561a895b52484b701d51a
+author A U Thor <author@example.com> 1465981137 +0000
+committer C O Mitter <committer@example.com> 1465981137 +0000
+gpgsig -----BEGIN PGP SIGNATURE-----
+ Version: GnuPG v1
+
+ iQEcBAABAgAGBQJXYRjRAAoJEGEJLoW3InGJ3IwIAIY4SA6GxY3BjL60YyvsJPh/
+ HRCJwH+w7wt3Yc/9/bW2F+gF72kdHOOs2jfv+OZhq0q4OAN6fvVSczISY/82LpS7
+ DVdMQj2/YcHDT4xrDNBnXnviDO9G7am/9OE77kEbXrp7QPxvhjkicHNwy2rEflAA
+ zn075rtEERDHr8nRYiDh8eVrefSO7D+bdQ7gv+7GsYMsd2auJWi1dHOSfTr9HIF4
+ HJhWXT9d2f8W+diRYXGh4X0wYiGg6na/soXc+vdtDYBzIxanRqjg8jCAeo1eOTk1
+ EdTwhcTZlI0x5pvJ3H0+4hA2jtldVtmPM4OTB0cTrEWBad7XV6YgiyuII73Ve3I=
+ =jKHM
+ -----END PGP SIGNATURE-----
+
+signed commit
+
+signed commit message body
+----
+
+- verify with: `git verify-commit [-v]` (or `git show --show-signature`)
+
+----
+gpg: Signature made Wed Jun 15 10:58:57 2016 CEST using RSA key ID B7227189
+gpg: Good signature from "Eris Discordia <discord@example.net>"
+gpg: WARNING: This key is not certified with a trusted signature!
+gpg: There is no indication that the signature belongs to the owner.
+Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
+tree eebfed94e75e7760540d1485c740902590a00332
+parent 04b871796dc0420f8e7561a895b52484b701d51a
+author A U Thor <author@example.com> 1465981137 +0000
+committer C O Mitter <committer@example.com> 1465981137 +0000
+
+signed commit
+
+signed commit message body
+----
+
+== Mergetag signatures
+
+- created by: `git merge` on signed tag
+- payload/embedding: the whole signed tag object is embedded into
+ the (merge) commit object as header entry `mergetag`
+- example: merge of the signed tag `signedtag` as above
+
+----
+tree c7b1cff039a93f3600a1d18b82d26688668c7dea
+parent c33429be94b5f2d3ee9b0adad223f877f174b05d
+parent 04b871796dc0420f8e7561a895b52484b701d51a
+author A U Thor <author@example.com> 1465982009 +0000
+committer C O Mitter <committer@example.com> 1465982009 +0000
+mergetag object 04b871796dc0420f8e7561a895b52484b701d51a
+ type commit
+ tag signedtag
+ tagger C O Mitter <committer@example.com> 1465981006 +0000
+
+ signed tag
+
+ signed tag message body
+ -----BEGIN PGP SIGNATURE-----
+ Version: GnuPG v1
+
+ iQEcBAABAgAGBQJXYRhOAAoJEGEJLoW3InGJklkIAIcnhL7RwEb/+QeX9enkXhxn
+ rxfdqrvWd1K80sl2TOt8Bg/NYwrUBw/RWJ+sg/hhHp4WtvE1HDGHlkEz3y11Lkuh
+ 8tSxS3qKTxXUGozyPGuE90sJfExhZlW4knIQ1wt/yWqM+33E9pN4hzPqLwyrdods
+ q8FWEqPPUbSJXoMbRPw04S5jrLtZSsUWbRYjmJCHzlhSfFWW4eFd37uquIaLUBS0
+ rkC3Jrx7420jkIpgFcTI2s60uhSQLzgcCwdA2ukSYIRnjg/zDkj8+3h/GaROJ72x
+ lZyI6HWixKJkWw8lE9aAOD9TmTW9sFJwcVAzmAuFX2kUreDUKMZduGcoRYGpD7E=
+ =jpXa
+ -----END PGP SIGNATURE-----
+
+Merge tag 'signedtag' into downstream
+
+signed tag
+
+signed tag message body
+
+# gpg: Signature made Wed Jun 15 08:56:46 2016 UTC using RSA key ID B7227189
+# gpg: Good signature from "Eris Discordia <discord@example.net>"
+# gpg: WARNING: This key is not certified with a trusted signature!
+# gpg: There is no indication that the signature belongs to the owner.
+# Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
+----
+
+- verify with: verification is embedded in merge commit message by default,
+ alternatively with `git show --show-signature`:
+
+----
+commit 9863f0c76ff78712b6800e199a46aa56afbcbd49
+merged tag 'signedtag'
+gpg: Signature made Wed Jun 15 10:56:46 2016 CEST using RSA key ID B7227189
+gpg: Good signature from "Eris Discordia <discord@example.net>"
+gpg: WARNING: This key is not certified with a trusted signature!
+gpg: There is no indication that the signature belongs to the owner.
+Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
+Merge: c33429b 04b8717
+Author: A U Thor <author@example.com>
+Date: Wed Jun 15 09:13:29 2016 +0000
+
+ Merge tag 'signedtag' into downstream
+
+ signed tag
+
+ signed tag message body
+
+ # gpg: Signature made Wed Jun 15 08:56:46 2016 UTC using RSA key ID B7227189
+ # gpg: Good signature from "Eris Discordia <discord@example.net>"
+ # gpg: WARNING: This key is not certified with a trusted signature!
+ # gpg: There is no indication that the signature belongs to the owner.
+ # Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
+----