mirror of
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865e99b5fd
Update the index format documentation to mention the v4 format.
* nd/doc-index-format:
update-index: list supported idx versions and their features
read-cache.c: use INDEX_FORMAT_{LB,UB} in verify_hdr()
index-format.txt: mention of v4 is missing in some places
200 lines
6.3 KiB
Text
200 lines
6.3 KiB
Text
Git index format
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================
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== The Git index file has the following format
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All binary numbers are in network byte order. Version 2 is described
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here unless stated otherwise.
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- A 12-byte header consisting of
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4-byte signature:
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The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")
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4-byte version number:
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The current supported versions are 2, 3 and 4.
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32-bit number of index entries.
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- A number of sorted index entries (see below).
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- Extensions
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Extensions are identified by signature. Optional extensions can
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be ignored if Git does not understand them.
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Git currently supports cached tree and resolve undo extensions.
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4-byte extension signature. If the first byte is 'A'..'Z' the
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extension is optional and can be ignored.
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32-bit size of the extension
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Extension data
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- 160-bit SHA-1 over the content of the index file before this
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checksum.
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== Index entry
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Index entries are sorted in ascending order on the name field,
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interpreted as a string of unsigned bytes (i.e. memcmp() order, no
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localization, no special casing of directory separator '/'). Entries
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with the same name are sorted by their stage field.
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32-bit ctime seconds, the last time a file's metadata changed
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this is stat(2) data
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32-bit ctime nanosecond fractions
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this is stat(2) data
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32-bit mtime seconds, the last time a file's data changed
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this is stat(2) data
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32-bit mtime nanosecond fractions
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this is stat(2) data
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32-bit dev
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this is stat(2) data
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32-bit ino
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this is stat(2) data
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32-bit mode, split into (high to low bits)
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4-bit object type
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valid values in binary are 1000 (regular file), 1010 (symbolic link)
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and 1110 (gitlink)
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3-bit unused
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9-bit unix permission. Only 0755 and 0644 are valid for regular files.
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Symbolic links and gitlinks have value 0 in this field.
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32-bit uid
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this is stat(2) data
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32-bit gid
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this is stat(2) data
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32-bit file size
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This is the on-disk size from stat(2), truncated to 32-bit.
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160-bit SHA-1 for the represented object
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A 16-bit 'flags' field split into (high to low bits)
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1-bit assume-valid flag
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1-bit extended flag (must be zero in version 2)
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2-bit stage (during merge)
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12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
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is stored in this field.
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(Version 3 or later) A 16-bit field, only applicable if the
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"extended flag" above is 1, split into (high to low bits).
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1-bit reserved for future
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1-bit skip-worktree flag (used by sparse checkout)
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1-bit intent-to-add flag (used by "git add -N")
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13-bit unused, must be zero
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Entry path name (variable length) relative to top level directory
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(without leading slash). '/' is used as path separator. The special
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path components ".", ".." and ".git" (without quotes) are disallowed.
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Trailing slash is also disallowed.
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The exact encoding is undefined, but the '.' and '/' characters
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are encoded in 7-bit ASCII and the encoding cannot contain a NUL
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byte (iow, this is a UNIX pathname).
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(Version 4) In version 4, the entry path name is prefix-compressed
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relative to the path name for the previous entry (the very first
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entry is encoded as if the path name for the previous entry is an
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empty string). At the beginning of an entry, an integer N in the
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variable width encoding (the same encoding as the offset is encoded
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for OFS_DELTA pack entries; see pack-format.txt) is stored, followed
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by a NUL-terminated string S. Removing N bytes from the end of the
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path name for the previous entry, and replacing it with the string S
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yields the path name for this entry.
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1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
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while keeping the name NUL-terminated.
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(Version 4) In version 4, the padding after the pathname does not
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exist.
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== Extensions
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=== Cached tree
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Cached tree extension contains pre-computed hashes for trees that can
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be derived from the index. It helps speed up tree object generation
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from index for a new commit.
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When a path is updated in index, the path must be invalidated and
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removed from tree cache.
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The signature for this extension is { 'T', 'R', 'E', 'E' }.
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A series of entries fill the entire extension; each of which
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consists of:
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- NUL-terminated path component (relative to its parent directory);
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- ASCII decimal number of entries in the index that is covered by the
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tree this entry represents (entry_count);
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- A space (ASCII 32);
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- ASCII decimal number that represents the number of subtrees this
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tree has;
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- A newline (ASCII 10); and
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- 160-bit object name for the object that would result from writing
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this span of index as a tree.
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An entry can be in an invalidated state and is represented by having
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a negative number in the entry_count field. In this case, there is no
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object name and the next entry starts immediately after the newline.
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When writing an invalid entry, -1 should always be used as entry_count.
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The entries are written out in the top-down, depth-first order. The
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first entry represents the root level of the repository, followed by the
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first subtree---let's call this A---of the root level (with its name
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relative to the root level), followed by the first subtree of A (with
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its name relative to A), ...
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=== Resolve undo
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A conflict is represented in the index as a set of higher stage entries.
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When a conflict is resolved (e.g. with "git add path"), these higher
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stage entries will be removed and a stage-0 entry with proper resoluton
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is added.
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When these higher stage entries are removed, they are saved in the
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resolve undo extension, so that conflicts can be recreated (e.g. with
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"git checkout -m"), in case users want to redo a conflict resolution
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from scratch.
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The signature for this extension is { 'R', 'E', 'U', 'C' }.
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A series of entries fill the entire extension; each of which
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consists of:
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- NUL-terminated pathname the entry describes (relative to the root of
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the repository, i.e. full pathname);
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- Three NUL-terminated ASCII octal numbers, entry mode of entries in
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stage 1 to 3 (a missing stage is represented by "0" in this field);
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and
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- At most three 160-bit object names of the entry in stages from 1 to 3
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(nothing is written for a missing stage).
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