[1/1] commit-graph: writing missing parents is a BUG

Commit Message

Linus Arver via GitGitGadget Dec. 19, 2018, 8:14 p.m. UTC

From: Derrick Stolee <[e-mail]>

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 <[e-mail]>
---
 commit-graph.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

Comments

Junio C Hamano Jan. 2, 2019, 11:01 p.m. UTC | #1

"Derrick Stolee via GitGitGadget" <[e-mail]> writes:

> From: Derrick Stolee <[e-mail]>
>
> 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 <[e-mail]>
> ---

Thanks, will queue.

Patch

diff --git a/commit-graph.c b/commit-graph.c
index 40c855f185..c14ada6918 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -34,7 +34,6 @@ 
 #define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1
 
 #define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
-#define GRAPH_PARENT_MISSING 0x7fffffff
 #define GRAPH_EDGE_LAST_MASK 0x7fffffff
 #define GRAPH_PARENT_NONE 0x70000000
 
@@ -496,7 +495,9 @@  static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 					      commit_to_sha1);
 
 			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);
@@ -514,7 +515,9 @@  static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 					      nr_commits,
 					      commit_to_sha1);
 			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);
@@ -567,7 +570,9 @@  static void write_graph_chunk_large_edges(struct hashfile *f,
 						  commit_to_sha1);
 
 			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)
 				edge_value |= GRAPH_LAST_EDGE;
 
@@ -864,7 +869,7 @@  void write_commit_graph(const char *obj_dir,
 			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);
 
 	commits.nr = 0;
@@ -891,7 +896,7 @@  void write_commit_graph(const char *obj_dir,
 	}
 	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"));
 
 	compute_generation_numbers(&commits, report_progress);