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commit-graph: writing missing parents is a BUG 

When writing a commit-graph, we write GRAPH_MISSING_PARENT if the
parent's object id does not appear in the list of commits to be
written into the commit-graph. This was done as the initial design
allowed commits to have missing parents, but the final version
requires the commit-graph to be closed under reachability. Thus,
this GRAPH_MISSING_PARENT value should never be written.

However, there are reasons why it could be written! These range
from a bug in the reachable-closure code to a memory error causing
the binary search into the list of object ids to fail. In either
case, we should fail fast and avoid writing the commit-graph file
with bad data.

Remove the GRAPH_MISSING_PARENT constant in favor of the constant
GRAPH_EDGE_LAST_MASK, which has the same value.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Derrick Stolee 2018-12-19 12:14:07 -08:00 committed by Junio C Hamano
parent 0d0ac3826a
commit cce99cd8c6
1 changed files with 11 additions and 6 deletions
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17
commit-graph.c
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@ -34,7 +34,6 @@
#define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1 #define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1


#define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000 #define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
#define GRAPH_PARENT_MISSING 0x7fffffff
#define GRAPH_EDGE_LAST_MASK 0x7fffffff #define GRAPH_EDGE_LAST_MASK 0x7fffffff
#define GRAPH_PARENT_NONE 0x70000000 #define GRAPH_PARENT_NONE 0x70000000


@ -496,7 +495,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
commit_to_sha1); commit_to_sha1);


if (edge_value < 0) if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING; BUG("missing parent %s for commit %s",
oid_to_hex(&parent->item->object.oid),
oid_to_hex(&(*list)->object.oid));
} }


hashwrite_be32(f, edge_value); hashwrite_be32(f, edge_value);
@ -514,7 +515,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
nr_commits, nr_commits,
commit_to_sha1); commit_to_sha1);
if (edge_value < 0) if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING; BUG("missing parent %s for commit %s",
oid_to_hex(&parent->item->object.oid),
oid_to_hex(&(*list)->object.oid));
} }


hashwrite_be32(f, edge_value); hashwrite_be32(f, edge_value);
@ -567,7 +570,9 @@ static void write_graph_chunk_large_edges(struct hashfile *f,
commit_to_sha1); commit_to_sha1);


if (edge_value < 0) if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING; BUG("missing parent %s for commit %s",
oid_to_hex(&parent->item->object.oid),
oid_to_hex(&(*list)->object.oid));
else if (!parent->next) else if (!parent->next)
edge_value |= GRAPH_LAST_EDGE; edge_value |= GRAPH_LAST_EDGE;


@ -864,7 +869,7 @@ void write_commit_graph(const char *obj_dir,
count_distinct++; count_distinct++;
} }


if (count_distinct >= GRAPH_PARENT_MISSING) if (count_distinct >= GRAPH_EDGE_LAST_MASK)
die(_("the commit graph format cannot write %d commits"), count_distinct); die(_("the commit graph format cannot write %d commits"), count_distinct);


commits.nr = 0; commits.nr = 0;
@ -891,7 +896,7 @@ void write_commit_graph(const char *obj_dir,
} }
num_chunks = num_extra_edges ? 4 : 3; num_chunks = num_extra_edges ? 4 : 3;


if (commits.nr >= GRAPH_PARENT_MISSING) if (commits.nr >= GRAPH_EDGE_LAST_MASK)
die(_("too many commits to write graph")); die(_("too many commits to write graph"));


compute_generation_numbers(&commits, report_progress); compute_generation_numbers(&commits, report_progress);