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commit-graph: add base graphs chunk

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To quickly verify a commit-graph chain is valid on load, we will
read from the new "Base Graphs Chunk" of each file in the chain.
This will prevent accidentally loading incorrect data from manually
editing the commit-graph-chain file or renaming graph-{hash}.graph
files.

The commit_graph struct already had an object_id struct "oid", but
it was never initialized or used. Add a line to read the hash from
the end of the commit-graph file and into the oid member.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee
2019-06-18 11:14:26 -07:00
committed by Junio C Hamano
parent 5c84b3396c
commit 118bd57002
3 changed files with 32 additions and 2 deletions
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11
Documentation/technical/commit-graph-format.txt
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@ -44,8 +44,9 @@ HEADER:
1-byte number (C) of "chunks"
1-byte (reserved for later use)
Current clients should ignore this value.
1-byte number (B) of base commit-graphs
We infer the length (H*B) of the Base Graphs chunk
from this value.
CHUNK LOOKUP:
@ -92,6 +93,12 @@ CHUNK DATA:
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.
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.