[PATCH v3 5/5] commit-graph.c: make 'commit-graph-chain's read-only

[Taylor Blau <me@ttaylorr.com>]

In a previous commit, we made incremental graph layers read-only by
using 'git_mkstemp_mode' with permissions '0444'.

There is no reason that 'commit-graph-chain's should be modifiable by
the user, since they are generated at a temporary location and then
atomically renamed into place.

To ensure that these files are read-only, too, use
'hold_lock_file_for_update_mode' with the same read-only permission
bits, and let the umask and 'adjust_shared_perm' take care of the rest.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 commit-graph.c                | 3 ++-
 t/t5324-split-commit-graph.sh | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/commit-graph.c b/commit-graph.c
index d05a55901d..b2dfd7701f 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1378,7 +1378,8 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	if (ctx->split) {
 		char *lock_name = get_chain_filename(ctx->odb);
 
-		hold_lock_file_for_update(&lk, lock_name, LOCK_DIE_ON_ERROR);
+		hold_lock_file_for_update_mode(&lk, lock_name,
+					       LOCK_DIE_ON_ERROR, 0444);
 
 		fd = git_mkstemp_mode(ctx->graph_name, 0444);
 		if (fd < 0) {
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 699c23d077..cff5a41f48 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -366,6 +366,8 @@ do
 		test_line_count = 1 graph-files &&
 		echo "$modebits" >expect &&
 		test_modebits $graphdir/graph-*.graph >actual &&
+		test_cmp expect actual &&
+		test_modebits $graphdir/commit-graph-chain >actual &&
 		test_cmp expect actual
 	'
 done <<\EOF
-- 
2.26.0.113.ge9739cdccc