docs: move commit-graph format docs to man section 5

Continue the move of existing Documentation/technical/* protocol and
file-format documentation into our main documentation space.

By moving the documentation for the commit-graph format into man
section 5 and the new "developerinterfaces" category. This change is
split from subsequent commits due to the relatively large amount of
ASCIIDOC formatting changes that are required.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 2 insertions, 168 deletions

diff --git a/Documentation/technical/chunk-format.txt b/Documentation/technical/chunk-format.txt
index 593614fced..f36ce42f37 100644
--- a/Documentation/technical/chunk-format.txt
+++ b/Documentation/technical/chunk-format.txt
@@ -6,7 +6,7 @@ sections of the file. This allows structured access to a large file by
 scanning a small "table of contents" for the remaining data. This common
 format is used by the `commit-graph` and `multi-pack-index` files. See
 link:technical/pack-format.html[the `multi-pack-index` format] and
-link:technical/commit-graph-format.html[the `commit-graph` format] for
+the `commit-graph` format in linkgit:gitformat-commit-graph[5] for
 how they use the chunks to describe structured data.
 
 A chunk-based file format begins with some header information custom to
@@ -108,7 +108,7 @@ for future formats:
 * *commit-graph:* see `write_commit_graph_file()` and `parse_commit_graph()`
   in `commit-graph.c` for how the chunk-format API is used to write and
   parse the commit-graph file format documented in
-  link:technical/commit-graph-format.html[the commit-graph file format].
+  the commit-graph file format in linkgit:gitformat-commit-graph[5].
 
 * *multi-pack-index:* see `write_midx_internal()` and `load_multi_pack_index()`
   in `midx.c` for how the chunk-format API is used to write and
diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
deleted file mode 100644
index 484b185ba9..0000000000
--- a/Documentation/technical/commit-graph-format.txt
+++ /dev/null
@@ -1,166 +0,0 @@
-Git commit graph format
-=======================
-
-The Git commit graph stores a list of commit OIDs and some associated
-metadata, including:
-
-- The generation number of the commit.
-
-- The root tree OID.
-
-- The commit date.
-
-- The parents of the commit, stored using positional references within
-  the graph file.
-
-- The Bloom filter of the commit carrying the paths that were changed between
-  the commit and its first parent, if requested.
-
-These positional references are stored as unsigned 32-bit integers
-corresponding to the array position within the list of commit OIDs. Due
-to some special constants we use to track parents, we can store at most
-(1 << 30) + (1 << 29) + (1 << 28) - 1 (around 1.8 billion) commits.
-
-== Commit graph files have the following format:
-
-In order to allow extensions that add extra data to the graph, we organize
-the body into "chunks" and provide a binary lookup table at the beginning
-of the body. The header includes certain values, such as number of chunks
-and hash type.
-
-All multi-byte numbers are in network byte order.
-
-HEADER:
-
-  4-byte signature:
-      The signature is: {'C', 'G', 'P', 'H'}
-
-  1-byte version number:
-      Currently, the only valid version is 1.
-
-  1-byte Hash Version
-      We infer the hash length (H) from this value:
-	1 => SHA-1
-	2 => SHA-256
-      If the hash type does not match the repository's hash algorithm, the
-      commit-graph file should be ignored with a warning presented to the
-      user.
-
-  1-byte number (C) of "chunks"
-
-  1-byte number (B) of base commit-graphs
-      We infer the length (H*B) of the Base Graphs chunk
-      from this value.
-
-CHUNK LOOKUP:
-
-  (C + 1) * 12 bytes listing the table of contents for the chunks:
-      First 4 bytes describe the chunk id. Value 0 is a terminating label.
-      Other 8 bytes provide the byte-offset in current file for chunk to
-      start. (Chunks are ordered contiguously in the file, so you can infer
-      the length using the next chunk position if necessary.) Each chunk
-      ID appears at most once.
-
-  The CHUNK LOOKUP matches the table of contents from
-  link:technical/chunk-format.html[the chunk-based file format].
-
-  The remaining data in the body is described one chunk at a time, and
-  these chunks may be given in any order. Chunks are required unless
-  otherwise specified.
-
-CHUNK DATA:
-
-  OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
-      The ith entry, F[i], stores the number of OIDs with first
-      byte at most i. Thus F[255] stores the total
-      number of commits (N).
-
-  OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
-      The OIDs for all commits in the graph, sorted in ascending order.
-
-  Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
-    * The first H bytes are for the OID of the root tree.
-    * The next 8 bytes are for the positions of the first two parents
-      of the ith commit. Stores value 0x70000000 if no parent in that
-      position. If there are more than two parents, the second value
-      has its most-significant bit on and the other bits store an array
-      position into the Extra Edge List chunk.
-    * The next 8 bytes store the topological level (generation number v1)
-      of the commit and
-      the commit time in seconds since EPOCH. The generation number
-      uses the higher 30 bits of the first 4 bytes, while the commit
-      time uses the 32 bits of the second 4 bytes, along with the lowest
-      2 bits of the lowest byte, storing the 33rd and 34th bit of the
-      commit time.
-
-  Generation Data (ID: {'G', 'D', 'A', '2' }) (N * 4 bytes) [Optional]
-    * This list of 4-byte values store corrected commit date offsets for the
-      commits, arranged in the same order as commit data chunk.
-    * If the corrected commit date offset cannot be stored within 31 bits,
-      the value has its most-significant bit on and the other bits store
-      the position of corrected commit date into the Generation Data Overflow
-      chunk.
-    * Generation Data chunk is present only when commit-graph file is written
-      by compatible versions of Git and in case of split commit-graph chains,
-      the topmost layer also has Generation Data chunk.
-
-  Generation Data Overflow (ID: {'G', 'D', 'O', '2' }) [Optional]
-    * This list of 8-byte values stores the corrected commit date offsets
-      for commits with corrected commit date offsets that cannot be
-      stored within 31 bits.
-    * Generation Data Overflow chunk is present only when Generation Data
-      chunk is present and atleast one corrected commit date offset cannot
-      be stored within 31 bits.
-
-  Extra Edge List (ID: {'E', 'D', 'G', 'E'}) [Optional]
-      This list of 4-byte values store the second through nth parents for
-      all octopus merges. The second parent value in the commit data stores
-      an array position within this list along with the most-significant bit
-      on. Starting at that array position, iterate through this list of commit
-      positions for the parents until reaching a value with the most-significant
-      bit on. The other bits correspond to the position of the last parent.
-
-  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
-    * The ith entry, BIDX[i], stores the number of bytes in all Bloom filters
-      from commit 0 to commit i (inclusive) in lexicographic order. The Bloom
-      filter for the i-th commit spans from BIDX[i-1] to BIDX[i] (plus header
-      length), where BIDX[-1] is 0.
-    * The BIDX chunk is ignored if the BDAT chunk is not present.
-
-  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
-    * It starts with header consisting of three unsigned 32-bit integers:
-      - Version of the hash algorithm being used. We currently only support
-	value 1 which corresponds to the 32-bit version of the murmur3 hash
-	implemented exactly as described in
-	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
-	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
-	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
-	in Probabilistic Verification"
-      - The number of times a path is hashed and hence the number of bit positions
-	      that cumulatively determine whether a file is present in the commit.
-      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
-	      contains 'n' entries, then the filter size is the minimum number of 64-bit
-	      words that contain n*b bits.
-    * The rest of the chunk is the concatenation of all the computed Bloom
-      filters for the commits in lexicographic order.
-    * Note: Commits with no changes or more than 512 changes have Bloom filters
-      of length one, with either all bits set to zero or one respectively.
-    * The BDAT chunk is present if and only if BIDX is present.
-
-  Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
-      This list of H-byte hashes describe a set of B commit-graph files that
-      form a commit-graph chain. The graph position for the ith commit in this
-      file's OID Lookup chunk is equal to i plus the number of commits in all
-      base graphs.  If B is non-zero, this chunk must exist.
-
-TRAILER:
-
-	H-byte HASH-checksum of all of the above.
-
-== Historical Notes:
-
-The Generation Data (GDA2) and Generation Data Overflow (GDO2) chunks have
-the number '2' in their chunk IDs because a previous version of Git wrote
-possibly erroneous data in these chunks with the IDs "GDAT" and "GDOV". By
-changing the IDs, newer versions of Git will silently ignore those older
-chunks and write the new information without trusting the incorrect data.