Merge branch 'jc/maint-fnmatch-old-style-definition' into maint
[git/git.git] / Documentation / technical / index-format.txt
1 GIT index format
2 ================
3
4 == The git index file has the following format
5
6 All binary numbers are in network byte order. Version 2 is described
7 here unless stated otherwise.
8
9 - A 12-byte header consisting of
10
11 4-byte signature:
12 The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")
13
14 4-byte version number:
15 The current supported versions are 2 and 3.
16
17 32-bit number of index entries.
18
19 - A number of sorted index entries (see below).
20
21 - Extensions
22
23 Extensions are identified by signature. Optional extensions can
24 be ignored if GIT does not understand them.
25
26 GIT currently supports cached tree and resolve undo extensions.
27
28 4-byte extension signature. If the first byte is 'A'..'Z' the
29 extension is optional and can be ignored.
30
31 32-bit size of the extension
32
33 Extension data
34
35 - 160-bit SHA-1 over the content of the index file before this
36 checksum.
37
38 == Index entry
39
40 Index entries are sorted in ascending order on the name field,
41 interpreted as a string of unsigned bytes (i.e. memcmp() order, no
42 localization, no special casing of directory separator '/'). Entries
43 with the same name are sorted by their stage field.
44
45 32-bit ctime seconds, the last time a file's metadata changed
46 this is stat(2) data
47
48 32-bit ctime nanosecond fractions
49 this is stat(2) data
50
51 32-bit mtime seconds, the last time a file's data changed
52 this is stat(2) data
53
54 32-bit mtime nanosecond fractions
55 this is stat(2) data
56
57 32-bit dev
58 this is stat(2) data
59
60 32-bit ino
61 this is stat(2) data
62
63 32-bit mode, split into (high to low bits)
64
65 4-bit object type
66 valid values in binary are 1000 (regular file), 1010 (symbolic link)
67 and 1110 (gitlink)
68
69 3-bit unused
70
71 9-bit unix permission. Only 0755 and 0644 are valid for regular files.
72 Symbolic links and gitlinks have value 0 in this field.
73
74 32-bit uid
75 this is stat(2) data
76
77 32-bit gid
78 this is stat(2) data
79
80 32-bit file size
81 This is the on-disk size from stat(2), truncated to 32-bit.
82
83 160-bit SHA-1 for the represented object
84
85 A 16-bit 'flags' field split into (high to low bits)
86
87 1-bit assume-valid flag
88
89 1-bit extended flag (must be zero in version 2)
90
91 2-bit stage (during merge)
92
93 12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
94 is stored in this field.
95
96 (Version 3) A 16-bit field, only applicable if the "extended flag"
97 above is 1, split into (high to low bits).
98
99 1-bit reserved for future
100
101 1-bit skip-worktree flag (used by sparse checkout)
102
103 1-bit intent-to-add flag (used by "git add -N")
104
105 13-bit unused, must be zero
106
107 Entry path name (variable length) relative to top level directory
108 (without leading slash). '/' is used as path separator. The special
109 path components ".", ".." and ".git" (without quotes) are disallowed.
110 Trailing slash is also disallowed.
111
112 The exact encoding is undefined, but the '.' and '/' characters
113 are encoded in 7-bit ASCII and the encoding cannot contain a NUL
114 byte (iow, this is a UNIX pathname).
115
116 (Version 4) In version 4, the entry path name is prefix-compressed
117 relative to the path name for the previous entry (the very first
118 entry is encoded as if the path name for the previous entry is an
119 empty string). At the beginning of an entry, an integer N in the
120 variable width encoding (the same encoding as the offset is encoded
121 for OFS_DELTA pack entries; see pack-format.txt) is stored, followed
122 by a NUL-terminated string S. Removing N bytes from the end of the
123 path name for the previous entry, and replacing it with the string S
124 yields the path name for this entry.
125
126 1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
127 while keeping the name NUL-terminated.
128
129 (Version 4) In version 4, the padding after the pathname does not
130 exist.
131
132 == Extensions
133
134 === Cached tree
135
136 Cached tree extension contains pre-computed hashes for trees that can
137 be derived from the index. It helps speed up tree object generation
138 from index for a new commit.
139
140 When a path is updated in index, the path must be invalidated and
141 removed from tree cache.
142
143 The signature for this extension is { 'T', 'R', 'E', 'E' }.
144
145 A series of entries fill the entire extension; each of which
146 consists of:
147
148 - NUL-terminated path component (relative to its parent directory);
149
150 - ASCII decimal number of entries in the index that is covered by the
151 tree this entry represents (entry_count);
152
153 - A space (ASCII 32);
154
155 - ASCII decimal number that represents the number of subtrees this
156 tree has;
157
158 - A newline (ASCII 10); and
159
160 - 160-bit object name for the object that would result from writing
161 this span of index as a tree.
162
163 An entry can be in an invalidated state and is represented by having
164 a negative number in the entry_count field. In this case, there is no
165 object name and the next entry starts immediately after the newline.
166 When writing an invalid entry, -1 should always be used as entry_count.
167
168 The entries are written out in the top-down, depth-first order. The
169 first entry represents the root level of the repository, followed by the
170 first subtree---let's call this A---of the root level (with its name
171 relative to the root level), followed by the first subtree of A (with
172 its name relative to A), ...
173
174 === Resolve undo
175
176 A conflict is represented in the index as a set of higher stage entries.
177 When a conflict is resolved (e.g. with "git add path"), these higher
178 stage entries will be removed and a stage-0 entry with proper resoluton
179 is added.
180
181 When these higher stage entries are removed, they are saved in the
182 resolve undo extension, so that conflicts can be recreated (e.g. with
183 "git checkout -m"), in case users want to redo a conflict resolution
184 from scratch.
185
186 The signature for this extension is { 'R', 'E', 'U', 'C' }.
187
188 A series of entries fill the entire extension; each of which
189 consists of:
190
191 - NUL-terminated pathname the entry describes (relative to the root of
192 the repository, i.e. full pathname);
193
194 - Three NUL-terminated ASCII octal numbers, entry mode of entries in
195 stage 1 to 3 (a missing stage is represented by "0" in this field);
196 and
197
198 - At most three 160-bit object names of the entry in stages from 1 to 3
199 (nothing is written for a missing stage).
200