| 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. |
| |
| == 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). |
| |