Re: [PATCH] doc: technical details about the index file format
From: Robin Rosenberg <hidden>
Date: 2016-06-15 22:49:27
onsdagen den 1 september 2010 11.53.45 skrev Nguyễn Thái Ngọc Duy:
This bases on the original work by Robin Rosenberg: http://thread.gmane.org/gmane.comp.version-control.git/73471
No need for this. My name is enough
Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
Add Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
quoted hunk ↗ jump to hunk
--- I split index entry out so the overall format is clearer. Other changes: - mention of version 3 - added ino and mode - added extended flags (v3) - entry sort order Again I don't realy know REUC extension, so only placeholder Documentation/technical/index-format.txt | 139 ++++++++++++++++++++++++++++++ 1 files changed, 139 insertions(+), 0 deletions(-) create mode 100644 Documentation/technical/index-format.txtdiff --git a/Documentation/technical/index-format.txtb/Documentation/technical/index-format.txt new file mode 100644 index 0000000..3e113ca--- /dev/null +++ b/Documentation/technical/index-format.txt@@ -0,0 +1,139 @@ +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' } + + 4-byte version number: + The current supported versions are 2 and 3. + + 32-bit number of index entries. + + - A number of sorted index entries + + - Extensions + + Extensions are identified by signature. Optional extensions can + be ignored if GIT does not understand them. + + GIT currently supports tree cache 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 with memcmp() by entry name. Entries with + the same name are sorted by their stage.
Index entries are sorted in ascending order on the name field, interpreted as a string of unsigned bytes.
+ + 32-bit ctime seconds, the last time a file's metadata changed + this is stat(2) data + + 32-bit ctime nanoseconds (modulo 1G) + 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 nanoseconds (modulo 1G) + 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 (blob), 1010 (symbolic link) + and 1110 (gitlink) + + 3-bit unused + + 9-bit unix permission (only 0755 and 0644 are valid) + + 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) + + 160-bit SHA-1 for the represented object + + A 16-bit 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 0x0FFF + + (Version 3) 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
...to the top level...
+ (without leading slash). '/' is used as path separator. Special
The special...
+ paths ".", ".." and ".git" (without quotes) are disallowed. + Trailing slash is also disallowed.
Why would anyone even consider adding a trailing slash to a _file_ name? The exact encoding is undefined, but the '.', and '/' characters are encoded in 7-bit ASCII and the encoding cannot contain a nul byte. Generally a superset of ASCII
+ + 1-8 nul bytes as necessary to pad the entry to a multiple ot eight bytes
...of eight bytes A typo of mine.
+ while keeping the name NUL-terminated.
+
+== Extensions
+
+=== Tree cache
+
+ Tree cache extension contains pre-computes hashes for all trees that
+ can be derived from the index
+
+ - Extension tag { 'T', 'R', 'E', 'E' }
+
+ - 32-bit size
+
+ - A number of entries
+
+ NUL-terminated tree name
+
+ Blank-terminated ASCII decimal number of entries in this tree
+
+ Newline-terminated position of this tree in the parent tree. 0 for
+ the root tree
+
+ 160-bit SHA-1 for this tree and it's children
+
+=== Resolve undo
+
+ TODO
+
+ - Extension tag { 'R', 'E', 'U', 'C' }
+
+ - 32-bit size