Merge branch 'tb/idx-midx-race-fix'

Processes that access packdata while the .idx file gets removed
(e.g. while repacking) did not fail or fall back gracefully as they
could.

* tb/idx-midx-race-fix:
  midx.c: protect against disappearing packs
  packfile.c: protect against disappearing indexes

Author: gitster

midx.c

@@ -298,7 +298,7 @@ static int nth_midxed_pack_entry(struct repository *r,
 	pack_int_id = nth_midxed_pack_int_id(m, pos);
 
 	if (prepare_midx_pack(r, m, pack_int_id))
-		die(_("error preparing packfile from multi-pack-index"));
+		return 0;
 	p = m->packs[pack_int_id];
 
 	/*

packfile.c

@@ -514,19 +514,8 @@ static int open_packed_git_1(struct packed_git *p)
 	ssize_t read_result;
 	const unsigned hashsz = the_hash_algo->rawsz;
 
-	if (!p->index_data) {
-		struct multi_pack_index *m;
-		const char *pack_name = pack_basename(p);
-
-		for (m = the_repository->objects->multi_pack_index;
-		     m; m = m->next) {
-			if (midx_contains_pack(m, pack_name))
-				break;
-		}
-
-		if (!m && open_pack_index(p))
-			return error("packfile %s index unavailable", p->pack_name);
-	}
+	if (open_pack_index(p))
+		return error("packfile %s index unavailable", p->pack_name);
 
 	if (!pack_max_fds) {
 		unsigned int max_fds = get_max_fd_limit();
@@ -567,10 +556,6 @@ static int open_packed_git_1(struct packed_git *p)
 			" supported (try upgrading GIT to a newer version)",
 			p->pack_name, ntohl(hdr.hdr_version));
 
-	/* Skip index checking if in multi-pack-index */
-	if (!p->index_data)
-		return 0;
-
 	/* Verify the pack matches its index. */
 	if (p->num_objects != ntohl(hdr.hdr_entries))
 		return error("packfile %s claims to have %"PRIu32" objects"

t/t5319-multi-pack-index.sh

@@ -138,7 +138,7 @@ test_expect_success 'write midx with one v2 pack' '
 
 compare_results_with_midx "one v2 pack"
 
-test_expect_success 'corrupt idx not opened' '
+test_expect_success 'corrupt idx reports errors' '
 	idx=$(test-tool read-midx $objdir | grep "\.idx\$") &&
 	mv $objdir/pack/$idx backup-$idx &&
 	test_when_finished "mv backup-\$idx \$objdir/pack/\$idx" &&
@@ -149,7 +149,7 @@ test_expect_success 'corrupt idx not opened' '
 	test_copy_bytes 1064 <backup-$idx >$objdir/pack/$idx &&
 
 	git -c core.multiPackIndex=true rev-list --objects --all 2>err &&
-	test_must_be_empty err
+	grep "index unavailable" err
 '
 
 test_expect_success 'add more objects' '
@@ -755,4 +755,30 @@ test_expect_success 'repack --batch-size=<large> repacks everything' '
 	)
 '
 
+test_expect_success 'load reverse index when missing .idx, .pack' '
+	git init repo &&
+	test_when_finished "rm -fr repo" &&
+	(
+		cd repo &&
+
+		git config core.multiPackIndex true &&
+
+		test_commit base &&
+		git repack -ad &&
+		git multi-pack-index write &&
+
+		git rev-parse HEAD >tip &&
+		pack=$(ls .git/objects/pack/pack-*.pack) &&
+		idx=$(ls .git/objects/pack/pack-*.idx) &&
+
+		mv $idx $idx.bak &&
+		git cat-file --batch-check="%(objectsize:disk)" <tip &&
+
+		mv $idx.bak $idx &&
+
+		mv $pack $pack.bak &&
+		git cat-file --batch-check="%(objectsize:disk)" <tip
+	)
+'
+
 test_done