1GITFORMAT-INDEX(5)                Git Manual                GITFORMAT-INDEX(5)
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NAME

6       gitformat-index - Git index format
7

SYNOPSIS

9       $GIT_DIR/index
10

DESCRIPTION

12       Git index format
13

THE GIT INDEX FILE HAS THE FOLLOWING FORMAT

15           All binary numbers are in network byte order.
16           In a repository using the traditional SHA-1, checksums and object IDs
17           (object names) mentioned below are all computed using SHA-1.  Similarly,
18           in SHA-256 repositories, these values are computed using SHA-256.
19           Version 2 is described here unless stated otherwise.
20
21       •   A 12-byte header consisting of
22
23               4-byte signature:
24                 The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")
25
26               4-byte version number:
27                 The current supported versions are 2, 3 and 4.
28
29               32-bit number of index entries.
30
31       •   A number of sorted index entries (see below).
32
33       •   Extensions
34
35               Extensions are identified by signature. Optional extensions can
36               be ignored if Git does not understand them.
37
38               4-byte extension signature. If the first byte is 'A'..'Z' the
39               extension is optional and can be ignored.
40
41               32-bit size of the extension
42
43               Extension data
44
45       •   Hash checksum over the content of the index file before this
46           checksum.
47

INDEX ENTRY

49           Index entries are sorted in ascending order on the name field,
50           interpreted as a string of unsigned bytes (i.e. memcmp() order, no
51           localization, no special casing of directory separator '/'). Entries
52           with the same name are sorted by their stage field.
53
54           An index entry typically represents a file. However, if sparse-checkout
55           is enabled in cone mode (`core.sparseCheckoutCone` is enabled) and the
56           `extensions.sparseIndex` extension is enabled, then the index may
57           contain entries for directories outside of the sparse-checkout definition.
58           These entries have mode `040000`, include the `SKIP_WORKTREE` bit, and
59           the path ends in a directory separator.
60
61           32-bit ctime seconds, the last time a file's metadata changed
62             this is stat(2) data
63
64           32-bit ctime nanosecond fractions
65             this is stat(2) data
66
67           32-bit mtime seconds, the last time a file's data changed
68             this is stat(2) data
69
70           32-bit mtime nanosecond fractions
71             this is stat(2) data
72
73           32-bit dev
74             this is stat(2) data
75
76           32-bit ino
77             this is stat(2) data
78
79           32-bit mode, split into (high to low bits)
80
81           16-bit unused, must be zero
82
83           4-bit object type
84             valid values in binary are 1000 (regular file), 1010 (symbolic link)
85             and 1110 (gitlink)
86
87           3-bit unused, must be zero
88
89           9-bit unix permission. Only 0755 and 0644 are valid for regular files.
90           Symbolic links and gitlinks have value 0 in this field.
91
92           32-bit uid
93             this is stat(2) data
94
95           32-bit gid
96             this is stat(2) data
97
98           32-bit file size
99             This is the on-disk size from stat(2), truncated to 32-bit.
100
101           Object name for the represented object
102
103           A 16-bit 'flags' field split into (high to low bits)
104
105           1-bit assume-valid flag
106
107           1-bit extended flag (must be zero in version 2)
108
109           2-bit stage (during merge)
110
111           12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
112           is stored in this field.
113
114           (Version 3 or later) A 16-bit field, only applicable if the
115           "extended flag" above is 1, split into (high to low bits).
116
117           1-bit reserved for future
118
119           1-bit skip-worktree flag (used by sparse checkout)
120
121           1-bit intent-to-add flag (used by "git add -N")
122
123           13-bit unused, must be zero
124
125           Entry path name (variable length) relative to top level directory
126             (without leading slash). '/' is used as path separator. The special
127             path components ".", ".." and ".git" (without quotes) are disallowed.
128             Trailing slash is also disallowed.
129
130           The exact encoding is undefined, but the '.' and '/' characters
131           are encoded in 7-bit ASCII and the encoding cannot contain a NUL
132           byte (iow, this is a UNIX pathname).
133
134           (Version 4) In version 4, the entry path name is prefix-compressed
135             relative to the path name for the previous entry (the very first
136             entry is encoded as if the path name for the previous entry is an
137             empty string).  At the beginning of an entry, an integer N in the
138             variable width encoding (the same encoding as the offset is encoded
139             for OFS_DELTA pack entries; see linkgit:gitformat-pack[5]) is stored, followed
140             by a NUL-terminated string S.  Removing N bytes from the end of the
141             path name for the previous entry, and replacing it with the string S
142             yields the path name for this entry.
143
144           1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
145           while keeping the name NUL-terminated.
146
147           (Version 4) In version 4, the padding after the pathname does not
148           exist.
149
150           Interpretation of index entries in split index mode is completely
151           different. See below for details.
152

EXTENSIONS

154   Cache tree
155           Since the index does not record entries for directories, the cache
156           entries cannot describe tree objects that already exist in the object
157           database for regions of the index that are unchanged from an existing
158           commit. The cache tree extension stores a recursive tree structure that
159           describes the trees that already exist and completely match sections of
160           the cache entries. This speeds up tree object generation from the index
161           for a new commit by only computing the trees that are "new" to that
162           commit. It also assists when comparing the index to another tree, such
163           as `HEAD^{tree}`, since sections of the index can be skipped when a tree
164           comparison demonstrates equality.
165
166           The recursive tree structure uses nodes that store a number of cache
167           entries, a list of subnodes, and an object ID (OID). The OID references
168           the existing tree for that node, if it is known to exist. The subnodes
169           correspond to subdirectories that themselves have cache tree nodes. The
170           number of cache entries corresponds to the number of cache entries in
171           the index that describe paths within that tree's directory.
172
173           The extension tracks the full directory structure in the cache tree
174           extension, but this is generally smaller than the full cache entry list.
175
176           When a path is updated in index, Git invalidates all nodes of the
177           recursive cache tree corresponding to the parent directories of that
178           path. We store these tree nodes as being "invalid" by using "-1" as the
179           number of cache entries. Invalid nodes still store a span of index
180           entries, allowing Git to focus its efforts when reconstructing a full
181           cache tree.
182
183           The signature for this extension is { 'T', 'R', 'E', 'E' }.
184
185           A series of entries fill the entire extension; each of which
186           consists of:
187
188       •   NUL-terminated path component (relative to its parent directory);
189
190       •   ASCII decimal number of entries in the index that is covered by the
191           tree this entry represents (entry_count);
192
193       •   A space (ASCII 32);
194
195       •   ASCII decimal number that represents the number of subtrees this
196           tree has;
197
198       •   A newline (ASCII 10); and
199
200       •   Object name for the object that would result from writing this span
201           of index as a tree.
202
203               An entry can be in an invalidated state and is represented by having
204               a negative number in the entry_count field. In this case, there is no
205               object name and the next entry starts immediately after the newline.
206               When writing an invalid entry, -1 should always be used as entry_count.
207
208               The entries are written out in the top-down, depth-first order.  The
209               first entry represents the root level of the repository, followed by the
210               first subtree--let's call this A--of the root level (with its name
211               relative to the root level), followed by the first subtree of A (with
212               its name relative to A), and so on. The specified number of subtrees
213               indicates when the current level of the recursive stack is complete.
214
215   Resolve undo
216           A conflict is represented in the index as a set of higher stage entries.
217           When a conflict is resolved (e.g. with "git add path"), these higher
218           stage entries will be removed and a stage-0 entry with proper resolution
219           is added.
220
221           When these higher stage entries are removed, they are saved in the
222           resolve undo extension, so that conflicts can be recreated (e.g. with
223           "git checkout -m"), in case users want to redo a conflict resolution
224           from scratch.
225
226           The signature for this extension is { 'R', 'E', 'U', 'C' }.
227
228           A series of entries fill the entire extension; each of which
229           consists of:
230
231       •   NUL-terminated pathname the entry describes (relative to the root
232           of the repository, i.e. full pathname);
233
234       •   Three NUL-terminated ASCII octal numbers, entry mode of entries in
235           stage 1 to 3 (a missing stage is represented by "0" in this field);
236           and
237
238       •   At most three object names of the entry in stages from 1 to 3
239           (nothing is written for a missing stage).
240
241   Split index
242           In split index mode, the majority of index entries could be stored
243           in a separate file. This extension records the changes to be made on
244           top of that to produce the final index.
245
246           The signature for this extension is { 'l', 'i', 'n', 'k' }.
247
248           The extension consists of:
249
250       •   Hash of the shared index file. The shared index file path is
251           $GIT_DIR/sharedindex.<hash>. If all bits are zero, the index does
252           not require a shared index file.
253
254       •   An ewah-encoded delete bitmap, each bit represents an entry in the
255           shared index. If a bit is set, its corresponding entry in the
256           shared index will be removed from the final index. Note, because a
257           delete operation changes index entry positions, but we do need
258           original positions in replace phase, it’s best to just mark entries
259           for removal, then do a mass deletion after replacement.
260
261       •   An ewah-encoded replace bitmap, each bit represents an entry in the
262           shared index. If a bit is set, its corresponding entry in the
263           shared index will be replaced with an entry in this index file. All
264           replaced entries are stored in sorted order in this index. The
265           first "1" bit in the replace bitmap corresponds to the first index
266           entry, the second "1" bit to the second entry and so on. Replaced
267           entries may have empty path names to save space.
268
269               The remaining index entries after replaced ones will be added to the
270               final index. These added entries are also sorted by entry name then
271               stage.
272

UNTRACKED CACHE

274           Untracked cache saves the untracked file list and necessary data to
275           verify the cache. The signature for this extension is { 'U', 'N',
276           'T', 'R' }.
277
278           The extension starts with
279
280       •   A sequence of NUL-terminated strings, preceded by the size of the
281           sequence in variable width encoding. Each string describes the
282           environment where the cache can be used.
283
284       •   Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
285           ctime field until "file size".
286
287       •   Stat data of core.excludesFile
288
289       •   32-bit dir_flags (see struct dir_struct)
290
291       •   Hash of $GIT_DIR/info/exclude. A null hash means the file does not
292           exist.
293
294       •   Hash of core.excludesFile. A null hash means the file does not
295           exist.
296
297       •   NUL-terminated string of per-dir exclude file name. This usually is
298           ".gitignore".
299
300       •   The number of following directory blocks, variable width encoding.
301           If this number is zero, the extension ends here with a following
302           NUL.
303
304       •   A number of directory blocks in depth-first-search order, each
305           consists of
306
307       •   The number of untracked entries, variable width encoding.
308
309       •   The number of sub-directory blocks, variable width encoding.
310
311       •   The directory name terminated by NUL.
312
313       •   A number of untracked file/dir names terminated by NUL.
314
315       The remaining data of each directory block is grouped by type:
316
317       •   An ewah bitmap, the n-th bit marks whether the n-th directory has
318           valid untracked cache entries.
319
320       •   An ewah bitmap, the n-th bit records "check-only" bit of
321           read_directory_recursive() for the n-th directory.
322
323       •   An ewah bitmap, the n-th bit indicates whether hash and stat data
324           is valid for the n-th directory and exists in the next data.
325
326       •   An array of stat data. The n-th data corresponds with the n-th
327           "one" bit in the previous ewah bitmap.
328
329       •   An array of hashes. The n-th hash corresponds with the n-th "one"
330           bit in the previous ewah bitmap.
331
332       •   One NUL.
333

FILE SYSTEM MONITOR CACHE

335           The file system monitor cache tracks files for which the core.fsmonitor
336           hook has told us about changes.  The signature for this extension is
337           { 'F', 'S', 'M', 'N' }.
338
339           The extension starts with
340
341       •   32-bit version number: the current supported versions are 1 and 2.
342
343       •   (Version 1) 64-bit time: the extension data reflects all changes
344           through the given time which is stored as the nanoseconds elapsed
345           since midnight, January 1, 1970.
346
347       •   (Version 2) A null terminated string: an opaque token defined by
348           the file system monitor application. The extension data reflects
349           all changes relative to that token.
350
351       •   32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
352
353       •   An ewah bitmap, the n-th bit indicates whether the n-th index entry
354           is not CE_FSMONITOR_VALID.
355

END OF INDEX ENTRY

357           The End of Index Entry (EOIE) is used to locate the end of the variable
358           length index entries and the beginning of the extensions. Code can take
359           advantage of this to quickly locate the index extensions without having
360           to parse through all of the index entries.
361
362           Because it must be able to be loaded before the variable length cache
363           entries and other index extensions, this extension must be written last.
364           The signature for this extension is { 'E', 'O', 'I', 'E' }.
365
366           The extension consists of:
367
368       •   32-bit offset to the end of the index entries
369
370       •   Hash over the extension types and their sizes (but not their
371           contents). E.g. if we have "TREE" extension that is N-bytes long,
372           "REUC" extension that is M-bytes long, followed by "EOIE", then the
373           hash would be:
374
375               Hash("TREE" + <binary representation of N> +
376                    "REUC" + <binary representation of M>)
377

INDEX ENTRY OFFSET TABLE

379           The Index Entry Offset Table (IEOT) is used to help address the CPU
380           cost of loading the index by enabling multi-threading the process of
381           converting cache entries from the on-disk format to the in-memory format.
382           The signature for this extension is { 'I', 'E', 'O', 'T' }.
383
384           The extension consists of:
385
386       •   32-bit version (currently 1)
387
388       •   A number of index offset entries each consisting of:
389
390       •   32-bit offset from the beginning of the file to the first cache
391           entry in this block of entries.
392
393       •   32-bit count of cache entries in this block
394

SPARSE DIRECTORY ENTRIES

396           When using sparse-checkout in cone mode, some entire directories within
397           the index can be summarized by pointing to a tree object instead of the
398           entire expanded list of paths within that tree. An index containing such
399           entries is a "sparse index". Index format versions 4 and less were not
400           implemented with such entries in mind. Thus, for these versions, an
401           index containing sparse directory entries will include this extension
402           with signature { 's', 'd', 'i', 'r' }. Like the split-index extension,
403           tools should avoid interacting with a sparse index unless they understand
404           this extension.
405

GIT

407       Part of the git(1) suite
408
409
410
411Git 2.43.0                        11/20/2023                GITFORMAT-INDEX(5)
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