technical/index-format.html - external/gitster/git-htmldocs - Git at Google

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 </head>
 <body class="article">
 <div id="header">
 <h1>Git index format</h1>
 </div>
 <div id="content">
 <div class="sect1">
 <h2 id="_the_git_index_file_has_the_following_format">The Git index file has the following format</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>All binary numbers are in network byte order. Version 2 is described
 here unless stated otherwise.</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 A 12-byte header consisting of
 </p>
 <div class="literalblock">
 <div class="content">
 <pre><code>4-byte signature:
  The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>4-byte version number:
  The current supported versions are 2, 3 and 4.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit number of index entries.</code></pre>
 </div></div>
 </li>
 <li>
 <p>
 A number of sorted index entries (see below).
 </p>
 </li>
 <li>
 <p>
 Extensions
 </p>
 <div class="literalblock">
 <div class="content">
 <pre><code>Extensions are identified by signature. Optional extensions can
 be ignored if Git does not understand them.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>Git currently supports cached tree and resolve undo extensions.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>4-byte extension signature. If the first byte is 'A'..'Z' the
 extension is optional and can be ignored.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit size of the extension</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>Extension data</code></pre>
 </div></div>
 </li>
 <li>
 <p>
 160-bit SHA-1 over the content of the index file before this
  checksum.
 </p>
 </li>
 </ul></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_index_entry">Index entry</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit ctime seconds, the last time a file's metadata changed
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit ctime nanosecond fractions
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit mtime seconds, the last time a file's data changed
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit mtime nanosecond fractions
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit dev
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit ino
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit mode, split into (high to low bits)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>4-bit object type
  valid values in binary are 1000 (regular file), 1010 (symbolic link)
  and 1110 (gitlink)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>3-bit unused</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>9-bit unix permission. Only 0755 and 0644 are valid for regular files.
 Symbolic links and gitlinks have value 0 in this field.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit uid
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit gid
  this is stat(2) data</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>32-bit file size
  This is the on-disk size from stat(2), truncated to 32-bit.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>160-bit SHA-1 for the represented object</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>A 16-bit 'flags' field split into (high to low bits)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-bit assume-valid flag</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-bit extended flag (must be zero in version 2)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>2-bit stage (during merge)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
 is stored in this field.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>(Version 3 or later) A 16-bit field, only applicable if the
 "extended flag" above is 1, split into (high to low bits).</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-bit reserved for future</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-bit skip-worktree flag (used by sparse checkout)</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-bit intent-to-add flag (used by "git add -N")</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>13-bit unused, must be zero</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>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).</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>(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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
 while keeping the name NUL-terminated.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>(Version 4) In version 4, the padding after the pathname does not
 exist.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>Interpretation of index entries in split index mode is completely
 different. See below for details.</code></pre>
 </div></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_extensions">Extensions</h2>
 <div class="sectionbody">
 <div class="sect2">
 <h3 id="_cached_tree">Cached tree</h3>
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>When a path is updated in index, the path must be invalidated and
 removed from tree cache.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The signature for this extension is { 'T', 'R', 'E', 'E' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>A series of entries fill the entire extension; each of which
 consists of:</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 NUL-terminated path component (relative to its parent directory);
 </p>
 </li>
 <li>
 <p>
 ASCII decimal number of entries in the index that is covered by the
  tree this entry represents (entry_count);
 </p>
 </li>
 <li>
 <p>
 A space (ASCII 32);
 </p>
 </li>
 <li>
 <p>
 ASCII decimal number that represents the number of subtrees this
  tree has;
 </p>
 </li>
 <li>
 <p>
 A newline (ASCII 10); and
 </p>
 </li>
 <li>
 <p>
 160-bit object name for the object that would result from writing
  this span of index as a tree.
 </p>
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>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), ...</code></pre>
 </div></div>
 </li>
 </ul></div>
 </div>
 <div class="sect2">
 <h3 id="_resolve_undo">Resolve undo</h3>
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>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.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The signature for this extension is { 'R', 'E', 'U', 'C' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>A series of entries fill the entire extension; each of which
 consists of:</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 NUL-terminated pathname the entry describes (relative to the root of
  the repository, i.e. full pathname);
 </p>
 </li>
 <li>
 <p>
 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
 </p>
 </li>
 <li>
 <p>
 At most three 160-bit object names of the entry in stages from 1 to 3
  (nothing is written for a missing stage).
 </p>
 </li>
 </ul></div>
 </div>
 <div class="sect2">
 <h3 id="_split_index">Split index</h3>
 <div class="literalblock">
 <div class="content">
 <pre><code>In split index mode, the majority of index entries could be stored
 in a separate file. This extension records the changes to be made on
 top of that to produce the final index.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The signature for this extension is { 'l', 'i', 'n', 'k' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The extension consists of:</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 160-bit SHA-1 of the shared index file. The shared index file path
  is $GIT_DIR/sharedindex.&lt;SHA-1&gt;. If all 160 bits are zero, the
  index does not require a shared index file.
 </p>
 </li>
 <li>
 <p>
 An ewah-encoded delete bitmap, each bit represents an entry in the
  shared index. If a bit is set, its corresponding entry in the
  shared index will be removed from the final index. Note, because
  a delete operation changes index entry positions, but we do need
  original positions in replace phase, it&#8217;s best to just mark
  entries for removal, then do a mass deletion after replacement.
 </p>
 </li>
 <li>
 <p>
 An ewah-encoded replace bitmap, each bit represents an entry in
  the shared index. If a bit is set, its corresponding entry in the
  shared index will be replaced with an entry in this index
  file. All replaced entries are stored in sorted order in this
  index. The first "1" bit in the replace bitmap corresponds to the
  first index entry, the second "1" bit to the second entry and so
  on. Replaced entries may have empty path names to save space.
 </p>
 <div class="literalblock">
 <div class="content">
 <pre><code>The remaining index entries after replaced ones will be added to the
 final index. These added entries are also sorted by entry name then
 stage.</code></pre>
 </div></div>
 </li>
 </ul></div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_untracked_cache">Untracked cache</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>Untracked cache saves the untracked file list and necessary data to
 verify the cache. The signature for this extension is { 'U', 'N',
 'T', 'R' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The extension starts with</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 A sequence of NUL-terminated strings, preceded by the size of the
  sequence in variable width encoding. Each string describes the
  environment where the cache can be used.
 </p>
 </li>
 <li>
 <p>
 Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
  ctime field until "file size".
 </p>
 </li>
 <li>
 <p>
 Stat data of core.excludesfile
 </p>
 </li>
 <li>
 <p>
 32-bit dir_flags (see struct dir_struct)
 </p>
 </li>
 <li>
 <p>
 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
  does not exist.
 </p>
 </li>
 <li>
 <p>
 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does
  not exist.
 </p>
 </li>
 <li>
 <p>
 NUL-terminated string of per-dir exclude file name. This usually
  is ".gitignore".
 </p>
 </li>
 <li>
 <p>
 The number of following directory blocks, variable width
  encoding. If this number is zero, the extension ends here with a
  following NUL.
 </p>
 </li>
 <li>
 <p>
 A number of directory blocks in depth-first-search order, each
  consists of
 </p>
 </li>
 <li>
 <p>
 The number of untracked entries, variable width encoding.
 </p>
 </li>
 <li>
 <p>
 The number of sub-directory blocks, variable width encoding.
 </p>
 </li>
 <li>
 <p>
 The directory name terminated by NUL.
 </p>
 </li>
 <li>
 <p>
 A number of untracked file/dir names terminated by NUL.
 </p>
 </li>
 </ul></div>
 <div class="paragraph"><p>The remaining data of each directory block is grouped by type:</p></div>
 <div class="ulist"><ul>
 <li>
 <p>
 An ewah bitmap, the n-th bit marks whether the n-th directory has
  valid untracked cache entries.
 </p>
 </li>
 <li>
 <p>
 An ewah bitmap, the n-th bit records "check-only" bit of
  read_directory_recursive() for the n-th directory.
 </p>
 </li>
 <li>
 <p>
 An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
  is valid for the n-th directory and exists in the next data.
 </p>
 </li>
 <li>
 <p>
 An array of stat data. The n-th data corresponds with the n-th
  "one" bit in the previous ewah bitmap.
 </p>
 </li>
 <li>
 <p>
 An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
  in the previous ewah bitmap.
 </p>
 </li>
 <li>
 <p>
 One NUL.
 </p>
 </li>
 </ul></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_file_system_monitor_cache">File System Monitor cache</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>The file system monitor cache tracks files for which the core.fsmonitor
 hook has told us about changes. The signature for this extension is
 { 'F', 'S', 'M', 'N' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The extension starts with</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 32-bit version number: the current supported version is 1.
 </p>
 </li>
 <li>
 <p>
 64-bit time: the extension data reflects all changes through the given
  time which is stored as the nanoseconds elapsed since midnight,
  January 1, 1970.
 </p>
 </li>
 <li>
 <p>
 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
 </p>
 </li>
 <li>
 <p>
 An ewah bitmap, the n-th bit indicates whether the n-th index entry
  is not CE_FSMONITOR_VALID.
 </p>
 </li>
 </ul></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_end_of_index_entry">End of Index Entry</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>The End of Index Entry (EOIE) is used to locate the end of the variable
 length index entries and the begining of the extensions. Code can take
 advantage of this to quickly locate the index extensions without having
 to parse through all of the index entries.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>Because it must be able to be loaded before the variable length cache
 entries and other index extensions, this extension must be written last.
 The signature for this extension is { 'E', 'O', 'I', 'E' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The extension consists of:</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 32-bit offset to the end of the index entries
 </p>
 </li>
 <li>
 <p>
 160-bit SHA-1 over the extension types and their sizes (but not
  their contents). E.g. if we have "TREE" extension that is N-bytes
  long, "REUC" extension that is M-bytes long, followed by "EOIE",
  then the hash would be:
 </p>
 <div class="literalblock">
 <div class="content">
 <pre><code>SHA-1("TREE" + &lt;binary representation of N&gt; +
  "REUC" + &lt;binary representation of M&gt;)</code></pre>
 </div></div>
 </li>
 </ul></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_index_entry_offset_table">Index Entry Offset Table</h2>
 <div class="sectionbody">
 <div class="literalblock">
 <div class="content">
 <pre><code>The Index Entry Offset Table (IEOT) is used to help address the CPU
 cost of loading the index by enabling multi-threading the process of
 converting cache entries from the on-disk format to the in-memory format.
 The signature for this extension is { 'I', 'E', 'O', 'T' }.</code></pre>
 </div></div>
 <div class="literalblock">
 <div class="content">
 <pre><code>The extension consists of:</code></pre>
 </div></div>
 <div class="ulist"><ul>
 <li>
 <p>
 32-bit version (currently 1)
 </p>
 </li>
 <li>
 <p>
 A number of index offset entries each consisting of:
 </p>
 </li>
 <li>
 <p>
 32-bit offset from the begining of the file to the first cache entry
  in this block of entries.
 </p>
 </li>
 <li>
 <p>
 32-bit count of cache entries in this block
 </p>
 </li>
 </ul></div>
 </div>
 </div>
 </div>
 <div id="footnotes"><hr /></div>
 <div id="footer">
 <div id="footer-text">
 Last updated
  2018-10-19 14:42:33 JST
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