eoie: add End of Index Entry (EOIE) extension
[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, 3 and 4.
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 or later) A 16-bit field, only applicable if the
97 "extended flag" 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 Interpretation of index entries in split index mode is completely
133 different. See below for details.
134
135 == Extensions
136
137 === Cached tree
138
139 Cached tree extension contains pre-computed hashes for trees that can
140 be derived from the index. It helps speed up tree object generation
141 from index for a new commit.
142
143 When a path is updated in index, the path must be invalidated and
144 removed from tree cache.
145
146 The signature for this extension is { 'T', 'R', 'E', 'E' }.
147
148 A series of entries fill the entire extension; each of which
149 consists of:
150
151 - NUL-terminated path component (relative to its parent directory);
152
153 - ASCII decimal number of entries in the index that is covered by the
154 tree this entry represents (entry_count);
155
156 - A space (ASCII 32);
157
158 - ASCII decimal number that represents the number of subtrees this
159 tree has;
160
161 - A newline (ASCII 10); and
162
163 - 160-bit object name for the object that would result from writing
164 this span of index as a tree.
165
166 An entry can be in an invalidated state and is represented by having
167 a negative number in the entry_count field. In this case, there is no
168 object name and the next entry starts immediately after the newline.
169 When writing an invalid entry, -1 should always be used as entry_count.
170
171 The entries are written out in the top-down, depth-first order. The
172 first entry represents the root level of the repository, followed by the
173 first subtree--let's call this A--of the root level (with its name
174 relative to the root level), followed by the first subtree of A (with
175 its name relative to A), ...
176
177 === Resolve undo
178
179 A conflict is represented in the index as a set of higher stage entries.
180 When a conflict is resolved (e.g. with "git add path"), these higher
181 stage entries will be removed and a stage-0 entry with proper resolution
182 is added.
183
184 When these higher stage entries are removed, they are saved in the
185 resolve undo extension, so that conflicts can be recreated (e.g. with
186 "git checkout -m"), in case users want to redo a conflict resolution
187 from scratch.
188
189 The signature for this extension is { 'R', 'E', 'U', 'C' }.
190
191 A series of entries fill the entire extension; each of which
192 consists of:
193
194 - NUL-terminated pathname the entry describes (relative to the root of
195 the repository, i.e. full pathname);
196
197 - Three NUL-terminated ASCII octal numbers, entry mode of entries in
198 stage 1 to 3 (a missing stage is represented by "0" in this field);
199 and
200
201 - At most three 160-bit object names of the entry in stages from 1 to 3
202 (nothing is written for a missing stage).
203
204 === Split index
205
206 In split index mode, the majority of index entries could be stored
207 in a separate file. This extension records the changes to be made on
208 top of that to produce the final index.
209
210 The signature for this extension is { 'l', 'i', 'n', 'k' }.
211
212 The extension consists of:
213
214 - 160-bit SHA-1 of the shared index file. The shared index file path
215 is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the
216 index does not require a shared index file.
217
218 - An ewah-encoded delete bitmap, each bit represents an entry in the
219 shared index. If a bit is set, its corresponding entry in the
220 shared index will be removed from the final index. Note, because
221 a delete operation changes index entry positions, but we do need
222 original positions in replace phase, it's best to just mark
223 entries for removal, then do a mass deletion after replacement.
224
225 - An ewah-encoded replace bitmap, each bit represents an entry in
226 the shared index. If a bit is set, its corresponding entry in the
227 shared index will be replaced with an entry in this index
228 file. All replaced entries are stored in sorted order in this
229 index. The first "1" bit in the replace bitmap corresponds to the
230 first index entry, the second "1" bit to the second entry and so
231 on. Replaced entries may have empty path names to save space.
232
233 The remaining index entries after replaced ones will be added to the
234 final index. These added entries are also sorted by entry name then
235 stage.
236
237 == Untracked cache
238
239 Untracked cache saves the untracked file list and necessary data to
240 verify the cache. The signature for this extension is { 'U', 'N',
241 'T', 'R' }.
242
243 The extension starts with
244
245 - A sequence of NUL-terminated strings, preceded by the size of the
246 sequence in variable width encoding. Each string describes the
247 environment where the cache can be used.
248
249 - Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
250 ctime field until "file size".
251
252 - Stat data of core.excludesfile
253
254 - 32-bit dir_flags (see struct dir_struct)
255
256 - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
257 does not exist.
258
259 - 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does
260 not exist.
261
262 - NUL-terminated string of per-dir exclude file name. This usually
263 is ".gitignore".
264
265 - The number of following directory blocks, variable width
266 encoding. If this number is zero, the extension ends here with a
267 following NUL.
268
269 - A number of directory blocks in depth-first-search order, each
270 consists of
271
272 - The number of untracked entries, variable width encoding.
273
274 - The number of sub-directory blocks, variable width encoding.
275
276 - The directory name terminated by NUL.
277
278 - A number of untracked file/dir names terminated by NUL.
279
280 The remaining data of each directory block is grouped by type:
281
282 - An ewah bitmap, the n-th bit marks whether the n-th directory has
283 valid untracked cache entries.
284
285 - An ewah bitmap, the n-th bit records "check-only" bit of
286 read_directory_recursive() for the n-th directory.
287
288 - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
289 is valid for the n-th directory and exists in the next data.
290
291 - An array of stat data. The n-th data corresponds with the n-th
292 "one" bit in the previous ewah bitmap.
293
294 - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
295 in the previous ewah bitmap.
296
297 - One NUL.
298
299 == File System Monitor cache
300
301 The file system monitor cache tracks files for which the core.fsmonitor
302 hook has told us about changes. The signature for this extension is
303 { 'F', 'S', 'M', 'N' }.
304
305 The extension starts with
306
307 - 32-bit version number: the current supported version is 1.
308
309 - 64-bit time: the extension data reflects all changes through the given
310 time which is stored as the nanoseconds elapsed since midnight,
311 January 1, 1970.
312
313 - 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
314
315 - An ewah bitmap, the n-th bit indicates whether the n-th index entry
316 is not CE_FSMONITOR_VALID.
317
318 == End of Index Entry
319
320 The End of Index Entry (EOIE) is used to locate the end of the variable
321 length index entries and the begining of the extensions. Code can take
322 advantage of this to quickly locate the index extensions without having
323 to parse through all of the index entries.
324
325 Because it must be able to be loaded before the variable length cache
326 entries and other index extensions, this extension must be written last.
327 The signature for this extension is { 'E', 'O', 'I', 'E' }.
328
329 The extension consists of:
330
331 - 32-bit offset to the end of the index entries
332
333 - 160-bit SHA-1 over the extension types and their sizes (but not
334 their contents). E.g. if we have "TREE" extension that is N-bytes
335 long, "REUC" extension that is M-bytes long, followed by "EOIE",
336 then the hash would be:
337
338 SHA-1("TREE" + <binary representation of N> +
339 "REUC" + <binary representation of M>)