Merge branch 'ps/object-store-midx-dedup-info' into ps/packfile-store

* ps/object-store-midx-dedup-info:
  midx: compute paths via their source
  midx: stop duplicating info redundant with its owning source
  midx: write multi-pack indices via their source
  midx: load multi-pack indices via their source
  midx: drop redundant `struct repository` parameter
  odb: simplify calling `link_alt_odb_entry()`
  odb: return newly created in-memory sources
  odb: consistently use "dir" to refer to alternate's directory
  odb: allow `odb_find_source()` to fail
  odb: store locality in object database sources

15 files changed, 254 insertions, 248 deletions

diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 6656187f90..fe3ebaadad 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -102,7 +102,7 @@ static int graph_verify(int argc, const char **argv, const char *prefix,
 	if (opts.progress)
 		flags |= COMMIT_GRAPH_WRITE_PROGRESS;
 
-	source = odb_find_source(the_repository->objects, opts.obj_dir);
+	source = odb_find_source_or_die(the_repository->objects, opts.obj_dir);
 	graph_name = get_commit_graph_filename(source);
 	chain_name = get_commit_graph_chain_filename(source);
 	if (open_commit_graph(graph_name, &fd, &st))
@@ -291,7 +291,7 @@ static int graph_write(int argc, const char **argv, const char *prefix,
 	    git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
 		flags |= COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
-	source = odb_find_source(the_repository->objects, opts.obj_dir);
+	source = odb_find_source_or_die(the_repository->objects, opts.obj_dir);
 
 	if (opts.reachable) {
 		if (write_commit_graph_reachable(source, flags, &write_opts))
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index d3b9e98be3..5f364aa816 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -65,12 +65,20 @@ static int parse_object_dir(const struct option *opt, const char *arg,
 	char **value = opt->value;
 	free(*value);
 	if (unset)
-		*value = xstrdup(repo_get_object_directory(the_repository));
+		*value = xstrdup(the_repository->objects->sources->path);
 	else
 		*value = real_pathdup(arg, 1);
 	return 0;
 }
 
+static struct odb_source *handle_object_dir_option(struct repository *repo)
+{
+	struct odb_source *source = odb_find_source(repo->objects, opts.object_dir);
+	if (!source)
+		source = odb_add_to_alternates_memory(repo->objects, opts.object_dir);
+	return source;
+}
+
 static struct option common_opts[] = {
 	OPT_CALLBACK(0, "object-dir", &opts.object_dir,
 	  N_("directory"),
@@ -140,6 +148,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 			     N_("refs snapshot for selecting bitmap commits")),
 		OPT_END(),
 	};
+	struct odb_source *source;
 	int ret;
 
 	opts.flags |= MIDX_WRITE_BITMAP_HASH_CACHE;
@@ -158,6 +167,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_write_usage,
 				   options);
+	source = handle_object_dir_option(repo);
 
 	FREE_AND_NULL(options);
 
@@ -166,7 +176,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 
 		read_packs_from_stdin(&packs);
 
-		ret = write_midx_file_only(repo, opts.object_dir, &packs,
+		ret = write_midx_file_only(source, &packs,
 					   opts.preferred_pack,
 					   opts.refs_snapshot, opts.flags);
 
@@ -177,7 +187,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 
 	}
 
-	ret = write_midx_file(repo, opts.object_dir, opts.preferred_pack,
+	ret = write_midx_file(source, opts.preferred_pack,
 			      opts.refs_snapshot, opts.flags);
 
 	free(opts.refs_snapshot);
@@ -194,6 +204,8 @@ static int cmd_multi_pack_index_verify(int argc, const char **argv,
 			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
+	struct odb_source *source;
+
 	options = add_common_options(builtin_multi_pack_index_verify_options);
 
 	trace2_cmd_mode(argv[0]);
@@ -206,10 +218,11 @@ static int cmd_multi_pack_index_verify(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_verify_usage,
 				   options);
+	source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return verify_midx_file(the_repository, opts.object_dir, opts.flags);
+	return verify_midx_file(source, opts.flags);
 }
 
 static int cmd_multi_pack_index_expire(int argc, const char **argv,
@@ -222,6 +235,8 @@ static int cmd_multi_pack_index_expire(int argc, const char **argv,
 			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
+	struct odb_source *source;
+
 	options = add_common_options(builtin_multi_pack_index_expire_options);
 
 	trace2_cmd_mode(argv[0]);
@@ -234,10 +249,11 @@ static int cmd_multi_pack_index_expire(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_expire_usage,
 				   options);
+	source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return expire_midx_packs(the_repository, opts.object_dir, opts.flags);
+	return expire_midx_packs(source, opts.flags);
 }
 
 static int cmd_multi_pack_index_repack(int argc, const char **argv,
@@ -252,6 +268,7 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 		  N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
+	struct odb_source *source;
 
 	options = add_common_options(builtin_multi_pack_index_repack_options);
 
@@ -266,11 +283,11 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_repack_usage,
 				   options);
+	source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return midx_repack(the_repository, opts.object_dir,
-			   (size_t)opts.batch_size, opts.flags);
+	return midx_repack(source, (size_t)opts.batch_size, opts.flags);
 }
 
 int cmd_multi_pack_index(int argc,
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 53a2256250..1494afcf3d 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1741,7 +1741,7 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 		struct multi_pack_index *m = get_multi_pack_index(source);
 		struct pack_entry e;
 
-		if (m && fill_midx_entry(the_repository, oid, &e, m)) {
+		if (m && fill_midx_entry(m, oid, &e)) {
 			want = want_object_in_pack_one(e.p, oid, exclude, found_pack, found_offset, found_mtime);
 			if (want != -1)
 				return want;
diff --git a/builtin/repack.c b/builtin/repack.c
index a4def39197..c490a51e91 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -223,9 +223,10 @@ static void mark_packs_for_deletion(struct existing_packs *existing,
 static void remove_redundant_pack(const char *dir_name, const char *base_name)
 {
 	struct strbuf buf = STRBUF_INIT;
-	struct multi_pack_index *m = get_multi_pack_index(the_repository->objects->sources);
+	struct odb_source *source = the_repository->objects->sources;
+	struct multi_pack_index *m = get_multi_pack_index(source);
 	strbuf_addf(&buf, "%s.pack", base_name);
-	if (m && m->local && midx_contains_pack(m, buf.buf))
+	if (m && source->local && midx_contains_pack(m, buf.buf))
 		clear_midx_file(the_repository);
 	strbuf_insertf(&buf, 0, "%s/", dir_name);
 	unlink_pack_path(buf.buf, 1);
@@ -1711,7 +1712,7 @@ int cmd_repack(int argc,
 		unsigned flags = 0;
 		if (git_env_bool(GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL, 0))
 			flags |= MIDX_WRITE_INCREMENTAL;
-		write_midx_file(the_repository, repo_get_object_directory(the_repository),
+		write_midx_file(the_repository->objects->sources,
 				NULL, NULL, flags);
 	}
 
diff --git a/midx-write.c b/midx-write.c
index a0aceab5e0..1e99f6a26e 100644
--- a/midx-write.c
+++ b/midx-write.c
@@ -26,9 +26,9 @@
 #define MIDX_CHUNK_LARGE_OFFSET_WIDTH (sizeof(uint64_t))
 
 extern int midx_checksum_valid(struct multi_pack_index *m);
-extern void clear_midx_files_ext(const char *object_dir, const char *ext,
+extern void clear_midx_files_ext(struct odb_source *source, const char *ext,
 				 const char *keep_hash);
-extern void clear_incremental_midx_files_ext(const char *object_dir,
+extern void clear_incremental_midx_files_ext(struct odb_source *source,
 					     const char *ext,
 					     const char **keep_hashes,
 					     uint32_t hashes_nr);
@@ -112,6 +112,7 @@ struct write_midx_context {
 	struct string_list *to_include;
 
 	struct repository *repo;
+	struct odb_source *source;
 };
 
 static int should_include_pack(const struct write_midx_context *ctx,
@@ -648,7 +649,6 @@ static uint32_t *midx_pack_order(struct write_midx_context *ctx)
 }
 
 static void write_midx_reverse_index(struct write_midx_context *ctx,
-				     const char *object_dir,
 				     unsigned char *midx_hash)
 {
 	struct strbuf buf = STRBUF_INIT;
@@ -657,11 +657,10 @@ static void write_midx_reverse_index(struct write_midx_context *ctx,
 	trace2_region_enter("midx", "write_midx_reverse_index", ctx->repo);
 
 	if (ctx->incremental)
-		get_split_midx_filename_ext(ctx->repo->hash_algo, &buf,
-					    object_dir, midx_hash,
-					    MIDX_EXT_REV);
+		get_split_midx_filename_ext(ctx->source, &buf,
+					    midx_hash, MIDX_EXT_REV);
 	else
-		get_midx_filename_ext(ctx->repo->hash_algo, &buf, object_dir,
+		get_midx_filename_ext(ctx->source, &buf,
 				      midx_hash, MIDX_EXT_REV);
 
 	tmp_file = write_rev_file_order(ctx->repo, NULL, ctx->pack_order,
@@ -836,7 +835,6 @@ static struct commit **find_commits_for_midx_bitmap(uint32_t *indexed_commits_nr
 }
 
 static int write_midx_bitmap(struct write_midx_context *ctx,
-			     const char *object_dir,
 			     const unsigned char *midx_hash,
 			     struct packing_data *pdata,
 			     struct commit **commits,
@@ -852,12 +850,11 @@ static int write_midx_bitmap(struct write_midx_context *ctx,
 	trace2_region_enter("midx", "write_midx_bitmap", ctx->repo);
 
 	if (ctx->incremental)
-		get_split_midx_filename_ext(ctx->repo->hash_algo, &bitmap_name,
-					    object_dir, midx_hash,
-					    MIDX_EXT_BITMAP);
+		get_split_midx_filename_ext(ctx->source, &bitmap_name,
+					    midx_hash, MIDX_EXT_BITMAP);
 	else
-		get_midx_filename_ext(ctx->repo->hash_algo, &bitmap_name,
-				      object_dir, midx_hash, MIDX_EXT_BITMAP);
+		get_midx_filename_ext(ctx->source, &bitmap_name,
+				      midx_hash, MIDX_EXT_BITMAP);
 
 	if (flags & MIDX_WRITE_BITMAP_HASH_CACHE)
 		options |= BITMAP_OPT_HASH_CACHE;
@@ -913,13 +910,6 @@ cleanup:
 	return ret;
 }
 
-static struct multi_pack_index *lookup_multi_pack_index(struct repository *r,
-							const char *object_dir)
-{
-	struct odb_source *source = odb_find_source(r->objects, object_dir);
-	return get_multi_pack_index(source);
-}
-
 static int fill_packs_from_midx(struct write_midx_context *ctx,
 				const char *preferred_pack_name, uint32_t flags)
 {
@@ -942,8 +932,7 @@ static int fill_packs_from_midx(struct write_midx_context *ctx,
 			 */
 			if (flags & MIDX_WRITE_REV_INDEX ||
 			    preferred_pack_name) {
-				if (prepare_midx_pack(ctx->repo, m,
-						      m->num_packs_in_base + i)) {
+				if (prepare_midx_pack(m, m->num_packs_in_base + i)) {
 					error(_("could not load pack"));
 					return 1;
 				}
@@ -989,10 +978,9 @@ static int link_midx_to_chain(struct multi_pack_index *m)
 	for (i = 0; i < ARRAY_SIZE(midx_exts); i++) {
 		const unsigned char *hash = get_midx_checksum(m);
 
-		get_midx_filename_ext(m->repo->hash_algo, &from, m->object_dir,
+		get_midx_filename_ext(m->source, &from,
 				      hash, midx_exts[i].non_split);
-		get_split_midx_filename_ext(m->repo->hash_algo, &to,
-					    m->object_dir, hash,
+		get_split_midx_filename_ext(m->source, &to, hash,
 					    midx_exts[i].split);
 
 		if (link(from.buf, to.buf) < 0 && errno != ENOENT) {
@@ -1011,7 +999,7 @@ done:
 	return ret;
 }
 
-static void clear_midx_files(struct repository *r, const char *object_dir,
+static void clear_midx_files(struct odb_source *source,
 			     const char **hashes, uint32_t hashes_nr,
 			     unsigned incremental)
 {
@@ -1030,16 +1018,16 @@ static void clear_midx_files(struct repository *r, const char *object_dir,
 	uint32_t i, j;
 
 	for (i = 0; i < ARRAY_SIZE(exts); i++) {
-		clear_incremental_midx_files_ext(object_dir, exts[i],
+		clear_incremental_midx_files_ext(source, exts[i],
 						 hashes, hashes_nr);
 		for (j = 0; j < hashes_nr; j++)
-			clear_midx_files_ext(object_dir, exts[i], hashes[j]);
+			clear_midx_files_ext(source, exts[i], hashes[j]);
 	}
 
 	if (incremental)
-		get_midx_filename(r->hash_algo, &buf, object_dir);
+		get_midx_filename(source, &buf);
 	else
-		get_midx_chain_filename(&buf, object_dir);
+		get_midx_chain_filename(source, &buf);
 
 	if (unlink(buf.buf) && errno != ENOENT)
 		die_errno(_("failed to clear multi-pack-index at %s"), buf.buf);
@@ -1047,13 +1035,14 @@ static void clear_midx_files(struct repository *r, const char *object_dir,
 	strbuf_release(&buf);
 }
 
-static int write_midx_internal(struct repository *r, const char *object_dir,
+static int write_midx_internal(struct odb_source *source,
 			       struct string_list *packs_to_include,
 			       struct string_list *packs_to_drop,
 			       const char *preferred_pack_name,
 			       const char *refs_snapshot,
 			       unsigned flags)
 {
+	struct repository *r = source->odb->repo;
 	struct strbuf midx_name = STRBUF_INIT;
 	unsigned char midx_hash[GIT_MAX_RAWSZ];
 	uint32_t i, start_pack;
@@ -1071,21 +1060,22 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 	trace2_region_enter("midx", "write_midx_internal", r);
 
 	ctx.repo = r;
+	ctx.source = source;
 
 	ctx.incremental = !!(flags & MIDX_WRITE_INCREMENTAL);
 
 	if (ctx.incremental)
 		strbuf_addf(&midx_name,
 			    "%s/pack/multi-pack-index.d/tmp_midx_XXXXXX",
-			    object_dir);
+			    source->path);
 	else
-		get_midx_filename(r->hash_algo, &midx_name, object_dir);
+		get_midx_filename(source, &midx_name);
 	if (safe_create_leading_directories(r, midx_name.buf))
 		die_errno(_("unable to create leading directories of %s"),
 			  midx_name.buf);
 
 	if (!packs_to_include || ctx.incremental) {
-		struct multi_pack_index *m = lookup_multi_pack_index(r, object_dir);
+		struct multi_pack_index *m = get_multi_pack_index(source);
 		if (m && !midx_checksum_valid(m)) {
 			warning(_("ignoring existing multi-pack-index; checksum mismatch"));
 			m = NULL;
@@ -1116,7 +1106,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 			if (flags & MIDX_WRITE_BITMAP && load_midx_revindex(m)) {
 				error(_("could not load reverse index for MIDX %s"),
 				      hash_to_hex_algop(get_midx_checksum(m),
-							m->repo->hash_algo));
+							m->source->odb->repo->hash_algo));
 				result = 1;
 				goto cleanup;
 			}
@@ -1139,7 +1129,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 
 	ctx.to_include = packs_to_include;
 
-	for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &ctx);
+	for_each_file_in_pack_dir(source->path, add_pack_to_midx, &ctx);
 	stop_progress(&ctx.progress);
 
 	if ((ctx.m && ctx.nr == ctx.m->num_packs + ctx.m->num_packs_in_base) &&
@@ -1159,7 +1149,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 			 * corresponding bitmap (or one wasn't requested).
 			 */
 			if (!want_bitmap)
-				clear_midx_files_ext(object_dir, "bitmap", NULL);
+				clear_midx_files_ext(source, "bitmap", NULL);
 			goto cleanup;
 		}
 	}
@@ -1327,7 +1317,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 	if (ctx.incremental) {
 		struct strbuf lock_name = STRBUF_INIT;
 
-		get_midx_chain_filename(&lock_name, object_dir);
+		get_midx_chain_filename(source, &lock_name);
 		hold_lock_file_for_update(&lk, lock_name.buf, LOCK_DIE_ON_ERROR);
 		strbuf_release(&lock_name);
 
@@ -1390,7 +1380,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 
 	if (flags & MIDX_WRITE_REV_INDEX &&
 	    git_env_bool("GIT_TEST_MIDX_WRITE_REV", 0))
-		write_midx_reverse_index(&ctx, object_dir, midx_hash);
+		write_midx_reverse_index(&ctx, midx_hash);
 
 	if (flags & MIDX_WRITE_BITMAP) {
 		struct packing_data pdata;
@@ -1413,7 +1403,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 		FREE_AND_NULL(ctx.entries);
 		ctx.entries_nr = 0;
 
-		if (write_midx_bitmap(&ctx, object_dir,
+		if (write_midx_bitmap(&ctx,
 				      midx_hash, &pdata, commits, commits_nr,
 				      flags) < 0) {
 			error(_("could not write multi-pack bitmap"));
@@ -1446,8 +1436,8 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 		if (link_midx_to_chain(ctx.base_midx) < 0)
 			return -1;
 
-		get_split_midx_filename_ext(r->hash_algo, &final_midx_name,
-					    object_dir, midx_hash, MIDX_EXT_MIDX);
+		get_split_midx_filename_ext(source, &final_midx_name,
+					    midx_hash, MIDX_EXT_MIDX);
 
 		if (rename_tempfile(&incr, final_midx_name.buf) < 0) {
 			error_errno(_("unable to rename new multi-pack-index layer"));
@@ -1480,7 +1470,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 	if (commit_lock_file(&lk) < 0)
 		die_errno(_("could not write multi-pack-index"));
 
-	clear_midx_files(r, object_dir, keep_hashes,
+	clear_midx_files(source, keep_hashes,
 			 ctx.num_multi_pack_indexes_before + 1,
 			 ctx.incremental);
 
@@ -1509,29 +1499,29 @@ cleanup:
 	return result;
 }
 
-int write_midx_file(struct repository *r, const char *object_dir,
+int write_midx_file(struct odb_source *source,
 		    const char *preferred_pack_name,
 		    const char *refs_snapshot, unsigned flags)
 {
-	return write_midx_internal(r, object_dir, NULL, NULL,
+	return write_midx_internal(source, NULL, NULL,
 				   preferred_pack_name, refs_snapshot,
 				   flags);
 }
 
-int write_midx_file_only(struct repository *r, const char *object_dir,
+int write_midx_file_only(struct odb_source *source,
 			 struct string_list *packs_to_include,
 			 const char *preferred_pack_name,
 			 const char *refs_snapshot, unsigned flags)
 {
-	return write_midx_internal(r, object_dir, packs_to_include, NULL,
+	return write_midx_internal(source, packs_to_include, NULL,
 				   preferred_pack_name, refs_snapshot, flags);
 }
 
-int expire_midx_packs(struct repository *r, const char *object_dir, unsigned flags)
+int expire_midx_packs(struct odb_source *source, unsigned flags)
 {
 	uint32_t i, *count, result = 0;
 	struct string_list packs_to_drop = STRING_LIST_INIT_DUP;
-	struct multi_pack_index *m = lookup_multi_pack_index(r, object_dir);
+	struct multi_pack_index *m = get_multi_pack_index(source);
 	struct progress *progress = NULL;
 
 	if (!m)
@@ -1544,7 +1534,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 
 	if (flags & MIDX_PROGRESS)
 		progress = start_delayed_progress(
-					  r,
+					  source->odb->repo,
 					  _("Counting referenced objects"),
 					  m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
@@ -1556,7 +1546,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 
 	if (flags & MIDX_PROGRESS)
 		progress = start_delayed_progress(
-					  r,
+					  source->odb->repo,
 					  _("Finding and deleting unreferenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
@@ -1566,7 +1556,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 		if (count[i])
 			continue;
 
-		if (prepare_midx_pack(r, m, i))
+		if (prepare_midx_pack(m, i))
 			continue;
 
 		if (m->packs[i]->pack_keep || m->packs[i]->is_cruft)
@@ -1584,7 +1574,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	free(count);
 
 	if (packs_to_drop.nr)
-		result = write_midx_internal(r, object_dir, NULL,
+		result = write_midx_internal(source, NULL,
 					     &packs_to_drop, NULL, NULL, flags);
 
 	string_list_clear(&packs_to_drop, 0);
@@ -1612,13 +1602,12 @@ static int compare_by_mtime(const void *a_, const void *b_)
 	return 0;
 }
 
-static int want_included_pack(struct repository *r,
-			      struct multi_pack_index *m,
+static int want_included_pack(struct multi_pack_index *m,
 			      int pack_kept_objects,
 			      uint32_t pack_int_id)
 {
 	struct packed_git *p;
-	if (prepare_midx_pack(r, m, pack_int_id))
+	if (prepare_midx_pack(m, pack_int_id))
 		return 0;
 	p = m->packs[pack_int_id];
 	if (!pack_kept_objects && p->pack_keep)
@@ -1640,7 +1629,7 @@ static void fill_included_packs_all(struct repository *r,
 	repo_config_get_bool(r, "repack.packkeptobjects", &pack_kept_objects);
 
 	for (i = 0; i < m->num_packs; i++) {
-		if (!want_included_pack(r, m, pack_kept_objects, i))
+		if (!want_included_pack(m, pack_kept_objects, i))
 			continue;
 
 		include_pack[i] = 1;
@@ -1664,7 +1653,7 @@ static void fill_included_packs_batch(struct repository *r,
 	for (i = 0; i < m->num_packs; i++) {
 		pack_info[i].pack_int_id = i;
 
-		if (prepare_midx_pack(r, m, i))
+		if (prepare_midx_pack(m, i))
 			continue;
 
 		pack_info[i].mtime = m->packs[i]->mtime;
@@ -1683,7 +1672,7 @@ static void fill_included_packs_batch(struct repository *r,
 		struct packed_git *p = m->packs[pack_int_id];
 		uint64_t expected_size;
 
-		if (!want_included_pack(r, m, pack_kept_objects, pack_int_id))
+		if (!want_included_pack(m, pack_kept_objects, pack_int_id))
 			continue;
 
 		/*
@@ -1710,14 +1699,15 @@ static void fill_included_packs_batch(struct repository *r,
 	free(pack_info);
 }
 
-int midx_repack(struct repository *r, const char *object_dir, size_t batch_size, unsigned flags)
+int midx_repack(struct odb_source *source, size_t batch_size, unsigned flags)
 {
+	struct repository *r = source->odb->repo;
 	int result = 0;
 	uint32_t i, packs_to_repack = 0;
 	unsigned char *include_pack;
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	FILE *cmd_in;
-	struct multi_pack_index *m = lookup_multi_pack_index(r, object_dir);
+	struct multi_pack_index *m = get_multi_pack_index(source);
 
 	/*
 	 * When updating the default for these configuration
@@ -1751,7 +1741,7 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
 
 	strvec_push(&cmd.args, "pack-objects");
 
-	strvec_pushf(&cmd.args, "%s/pack/pack", object_dir);
+	strvec_pushf(&cmd.args, "%s/pack/pack", source->path);
 
 	if (delta_base_offset)
 		strvec_push(&cmd.args, "--delta-base-offset");
@@ -1792,7 +1782,7 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
 		goto cleanup;
 	}
 
-	result = write_midx_internal(r, object_dir, NULL, NULL, NULL, NULL,
+	result = write_midx_internal(source, NULL, NULL, NULL, NULL,
 				     flags);
 
 cleanup:
diff --git a/midx.c b/midx.c
index 7d407682e6..7726c13d7e 100644
--- a/midx.c
+++ b/midx.c
@@ -16,9 +16,9 @@
 #define MIDX_PACK_ERROR ((void *)(intptr_t)-1)
 
 int midx_checksum_valid(struct multi_pack_index *m);
-void clear_midx_files_ext(const char *object_dir, const char *ext,
+void clear_midx_files_ext(struct odb_source *source, const char *ext,
 			  const char *keep_hash);
-void clear_incremental_midx_files_ext(const char *object_dir, const char *ext,
+void clear_incremental_midx_files_ext(struct odb_source *source, const char *ext,
 				      char **keep_hashes,
 				      uint32_t hashes_nr);
 int cmp_idx_or_pack_name(const char *idx_or_pack_name,
@@ -26,22 +26,20 @@ int cmp_idx_or_pack_name(const char *idx_or_pack_name,
 
 const unsigned char *get_midx_checksum(struct multi_pack_index *m)
 {
-	return m->data + m->data_len - m->repo->hash_algo->rawsz;
+	return m->data + m->data_len - m->source->odb->repo->hash_algo->rawsz;
 }
 
-void get_midx_filename(const struct git_hash_algo *hash_algo,
-		       struct strbuf *out, const char *object_dir)
+void get_midx_filename(struct odb_source *source, struct strbuf *out)
 {
-	get_midx_filename_ext(hash_algo, out, object_dir, NULL, NULL);
+	get_midx_filename_ext(source, out, NULL, NULL);
 }
 
-void get_midx_filename_ext(const struct git_hash_algo *hash_algo,
-			   struct strbuf *out, const char *object_dir,
+void get_midx_filename_ext(struct odb_source *source, struct strbuf *out,
 			   const unsigned char *hash, const char *ext)
 {
-	strbuf_addf(out, "%s/pack/multi-pack-index", object_dir);
+	strbuf_addf(out, "%s/pack/multi-pack-index", source->path);
 	if (ext)
-		strbuf_addf(out, "-%s.%s", hash_to_hex_algop(hash, hash_algo), ext);
+		strbuf_addf(out, "-%s.%s", hash_to_hex_algop(hash, source->odb->repo->hash_algo), ext);
 }
 
 static int midx_read_oid_fanout(const unsigned char *chunk_start,
@@ -95,11 +93,10 @@ static int midx_read_object_offsets(const unsigned char *chunk_start,
 	return 0;
 }
 
-static struct multi_pack_index *load_multi_pack_index_one(struct repository *r,
-							  const char *object_dir,
-							  const char *midx_name,
-							  int local)
+static struct multi_pack_index *load_multi_pack_index_one(struct odb_source *source,
+							  const char *midx_name)
 {
+	struct repository *r = source->odb->repo;
 	struct multi_pack_index *m = NULL;
 	int fd;
 	struct stat st;
@@ -129,11 +126,10 @@ static struct multi_pack_index *load_multi_pack_index_one(struct repository *r,
 	midx_map = xmmap(NULL, midx_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
 
-	FLEX_ALLOC_STR(m, object_dir, object_dir);
+	CALLOC_ARRAY(m, 1);
 	m->data = midx_map;
 	m->data_len = midx_size;
-	m->local = local;
-	m->repo = r;
+	m->source = source;
 
 	m->signature = get_be32(m->data);
 	if (m->signature != MIDX_SIGNATURE)
@@ -224,24 +220,23 @@ cleanup_fail:
 	return NULL;
 }
 
-void get_midx_chain_dirname(struct strbuf *buf, const char *object_dir)
+void get_midx_chain_dirname(struct odb_source *source, struct strbuf *buf)
 {
-	strbuf_addf(buf, "%s/pack/multi-pack-index.d", object_dir);
+	strbuf_addf(buf, "%s/pack/multi-pack-index.d", source->path);
 }
 
-void get_midx_chain_filename(struct strbuf *buf, const char *object_dir)
+void get_midx_chain_filename(struct odb_source *source, struct strbuf *buf)
 {
-	get_midx_chain_dirname(buf, object_dir);
+	get_midx_chain_dirname(source, buf);
 	strbuf_addstr(buf, "/multi-pack-index-chain");
 }
 
-void get_split_midx_filename_ext(const struct git_hash_algo *hash_algo,
-				 struct strbuf *buf, const char *object_dir,
+void get_split_midx_filename_ext(struct odb_source *source, struct strbuf *buf,
 				 const unsigned char *hash, const char *ext)
 {
-	get_midx_chain_dirname(buf, object_dir);
+	get_midx_chain_dirname(source, buf);
 	strbuf_addf(buf, "/multi-pack-index-%s.%s",
-		    hash_to_hex_algop(hash, hash_algo), ext);
+		    hash_to_hex_algop(hash, source->odb->repo->hash_algo), ext);
 }
 
 static int open_multi_pack_index_chain(const struct git_hash_algo *hash_algo,
@@ -297,19 +292,18 @@ static int add_midx_to_chain(struct multi_pack_index *midx,
 	return 1;
 }
 
-static struct multi_pack_index *load_midx_chain_fd_st(struct repository *r,
-						      const char *object_dir,
-						      int local,
+static struct multi_pack_index *load_midx_chain_fd_st(struct odb_source *source,
 						      int fd, struct stat *st,
 						      int *incomplete_chain)
 {
+	const struct git_hash_algo *hash_algo = source->odb->repo->hash_algo;
 	struct multi_pack_index *midx_chain = NULL;
 	struct strbuf buf = STRBUF_INIT;
 	int valid = 1;
 	uint32_t i, count;
 	FILE *fp = xfdopen(fd, "r");
 
-	count = st->st_size / (r->hash_algo->hexsz + 1);
+	count = st->st_size / (hash_algo->hexsz + 1);
 
 	for (i = 0; i < count; i++) {
 		struct multi_pack_index *m;
@@ -318,7 +312,7 @@ static struct multi_pack_index *load_midx_chain_fd_st(struct repository *r,
 		if (strbuf_getline_lf(&buf, fp) == EOF)
 			break;
 
-		if (get_oid_hex_algop(buf.buf, &layer, r->hash_algo)) {
+		if (get_oid_hex_algop(buf.buf, &layer, hash_algo)) {
 			warning(_("invalid multi-pack-index chain: line '%s' "
 				  "not a hash"),
 				buf.buf);
@@ -329,9 +323,9 @@ static struct multi_pack_index *load_midx_chain_fd_st(struct repository *r,
 		valid = 0;
 
 		strbuf_reset(&buf);
-		get_split_midx_filename_ext(r->hash_algo, &buf, object_dir,
+		get_split_midx_filename_ext(source, &buf,
 					    layer.hash, MIDX_EXT_MIDX);
-		m = load_multi_pack_index_one(r, object_dir, buf.buf, local);
+		m = load_multi_pack_index_one(source, buf.buf);
 
 		if (m) {
 			if (add_midx_to_chain(m, midx_chain)) {
@@ -354,40 +348,34 @@ static struct multi_pack_index *load_midx_chain_fd_st(struct repository *r,
 	return midx_chain;
 }
 
-static struct multi_pack_index *load_multi_pack_index_chain(struct repository *r,
-							    const char *object_dir,
-							    int local)
+static struct multi_pack_index *load_multi_pack_index_chain(struct odb_source *source)
 {
 	struct strbuf chain_file = STRBUF_INIT;
 	struct stat st;
 	int fd;
 	struct multi_pack_index *m = NULL;
 
-	get_midx_chain_filename(&chain_file, object_dir);
-	if (open_multi_pack_index_chain(r->hash_algo, chain_file.buf, &fd, &st)) {
+	get_midx_chain_filename(source, &chain_file);
+	if (open_multi_pack_index_chain(source->odb->repo->hash_algo, chain_file.buf, &fd, &st)) {
 		int incomplete;
 		/* ownership of fd is taken over by load function */
-		m = load_midx_chain_fd_st(r, object_dir, local, fd, &st,
-					  &incomplete);
+		m = load_midx_chain_fd_st(source, fd, &st, &incomplete);
 	}
 
 	strbuf_release(&chain_file);
 	return m;
 }
 
-struct multi_pack_index *load_multi_pack_index(struct repository *r,
-					       const char *object_dir,
-					       int local)
+struct multi_pack_index *load_multi_pack_index(struct odb_source *source)
 {
 	struct strbuf midx_name = STRBUF_INIT;
 	struct multi_pack_index *m;
 
-	get_midx_filename(r->hash_algo, &midx_name, object_dir);
+	get_midx_filename(source, &midx_name);
 
-	m = load_multi_pack_index_one(r, object_dir,
-				      midx_name.buf, local);
+	m = load_multi_pack_index_one(source, midx_name.buf);
 	if (!m)
-		m = load_multi_pack_index_chain(r, object_dir, local);
+		m = load_multi_pack_index_chain(source);
 
 	strbuf_release(&midx_name);
 
@@ -450,9 +438,10 @@ static uint32_t midx_for_pack(struct multi_pack_index **_m,
 	return pack_int_id - m->num_packs_in_base;
 }
 
-int prepare_midx_pack(struct repository *r, struct multi_pack_index *m,
+int prepare_midx_pack(struct multi_pack_index *m,
 		      uint32_t pack_int_id)
 {
+	struct repository *r = m->source->odb->repo;
 	struct strbuf pack_name = STRBUF_INIT;
 	struct strbuf key = STRBUF_INIT;
 	struct packed_git *p;
@@ -464,7 +453,7 @@ int prepare_midx_pack(struct repository *r, struct multi_pack_index *m,
 	if (m->packs[pack_int_id])
 		return 0;
 
-	strbuf_addf(&pack_name, "%s/pack/%s", m->object_dir,
+	strbuf_addf(&pack_name, "%s/pack/%s", m->source->path,
 		    m->pack_names[pack_int_id]);
 
 	/* pack_map holds the ".pack" name, but we have the .idx */
@@ -475,7 +464,8 @@ int prepare_midx_pack(struct repository *r, struct multi_pack_index *m,
 					strhash(key.buf), key.buf,
 					struct packed_git, packmap_ent);
 	if (!p) {
-		p = add_packed_git(r, pack_name.buf, pack_name.len, m->local);
+		p = add_packed_git(r, pack_name.buf, pack_name.len,
+				   m->source->local);
 		if (p) {
 			install_packed_git(r, p);
 			list_add_tail(&p->mru, &r->objects->packed_git_mru);
@@ -507,7 +497,7 @@ struct packed_git *nth_midxed_pack(struct multi_pack_index *m,
 
 #define MIDX_CHUNK_BITMAPPED_PACKS_WIDTH (2 * sizeof(uint32_t))
 
-int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
+int nth_bitmapped_pack(struct multi_pack_index *m,
 		       struct bitmapped_pack *bp, uint32_t pack_int_id)
 {
 	uint32_t local_pack_int_id = midx_for_pack(&m, pack_int_id);
@@ -515,7 +505,7 @@ int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
 	if (!m->chunk_bitmapped_packs)
 		return error(_("MIDX does not contain the BTMP chunk"));
 
-	if (prepare_midx_pack(r, m, pack_int_id))
+	if (prepare_midx_pack(m, pack_int_id))
 		return error(_("could not load bitmapped pack %"PRIu32), pack_int_id);
 
 	bp->p = m->packs[local_pack_int_id];
@@ -534,7 +524,8 @@ int bsearch_one_midx(const struct object_id *oid, struct multi_pack_index *m,
 		     uint32_t *result)
 {
 	int ret = bsearch_hash(oid->hash, m->chunk_oid_fanout,
-			       m->chunk_oid_lookup, m->repo->hash_algo->rawsz,
+			       m->chunk_oid_lookup,
+			       m->source->odb->repo->hash_algo->rawsz,
 			       result);
 	if (result)
 		*result += m->num_objects_in_base;
@@ -565,7 +556,7 @@ struct object_id *nth_midxed_object_oid(struct object_id *oid,
 	n = midx_for_object(&m, n);
 
 	oidread(oid, m->chunk_oid_lookup + st_mult(m->hash_len, n),
-		m->repo->hash_algo);
+		m->source->odb->repo->hash_algo);
 	return oid;
 }
 
@@ -600,10 +591,9 @@ uint32_t nth_midxed_pack_int_id(struct multi_pack_index *m, uint32_t pos)
 					       (off_t)pos * MIDX_CHUNK_OFFSET_WIDTH);
 }
 
-int fill_midx_entry(struct repository *r,
+int fill_midx_entry(struct multi_pack_index *m,
 		    const struct object_id *oid,
-		    struct pack_entry *e,
-		    struct multi_pack_index *m)
+		    struct pack_entry *e)
 {
 	uint32_t pos;
 	uint32_t pack_int_id;
@@ -615,7 +605,7 @@ int fill_midx_entry(struct repository *r,
 	midx_for_object(&m, pos);
 	pack_int_id = nth_midxed_pack_int_id(m, pos);
 
-	if (prepare_midx_pack(r, m, pack_int_id))
+	if (prepare_midx_pack(m, pack_int_id))
 		return 0;
 	p = m->packs[pack_int_id - m->num_packs_in_base];
 
@@ -723,7 +713,7 @@ int midx_preferred_pack(struct multi_pack_index *m, uint32_t *pack_int_id)
 	return 0;
 }
 
-int prepare_multi_pack_index_one(struct odb_source *source, int local)
+int prepare_multi_pack_index_one(struct odb_source *source)
 {
 	struct repository *r = source->odb->repo;
 
@@ -734,14 +724,14 @@ int prepare_multi_pack_index_one(struct odb_source *source, int local)
 	if (source->midx)
 		return 1;
 
-	source->midx = load_multi_pack_index(r, source->path, local);
+	source->midx = load_multi_pack_index(source);
 
 	return !!source->midx;
 }
 
 int midx_checksum_valid(struct multi_pack_index *m)
 {
-	return hashfile_checksum_valid(m->repo->hash_algo,
+	return hashfile_checksum_valid(m->source->odb->repo->hash_algo,
 				       m->data, m->data_len);
 }
 
@@ -768,7 +758,7 @@ static void clear_midx_file_ext(const char *full_path, size_t full_path_len UNUS
 		die_errno(_("failed to remove %s"), full_path);
 }
 
-void clear_midx_files_ext(const char *object_dir, const char *ext,
+void clear_midx_files_ext(struct odb_source *source, const char *ext,
 			  const char *keep_hash)
 {
 	struct clear_midx_data data;
@@ -782,7 +772,7 @@ void clear_midx_files_ext(const char *object_dir, const char *ext,
 	}
 	data.ext = ext;
 
-	for_each_file_in_pack_dir(object_dir,
+	for_each_file_in_pack_dir(source->path,
 				  clear_midx_file_ext,
 				  &data);
 
@@ -791,7 +781,7 @@ void clear_midx_files_ext(const char *object_dir, const char *ext,
 	free(data.keep);
 }
 
-void clear_incremental_midx_files_ext(const char *object_dir, const char *ext,
+void clear_incremental_midx_files_ext(struct odb_source *source, const char *ext,
 				      char **keep_hashes,
 				      uint32_t hashes_nr)
 {
@@ -807,7 +797,7 @@ void clear_incremental_midx_files_ext(const char *object_dir, const char *ext,
 	data.keep_nr = hashes_nr;
 	data.ext = ext;
 
-	for_each_file_in_pack_subdir(object_dir, "multi-pack-index.d",
+	for_each_file_in_pack_subdir(source->path, "multi-pack-index.d",
 				     clear_midx_file_ext, &data);
 
 	for (i = 0; i < hashes_nr; i++)
@@ -819,7 +809,7 @@ void clear_midx_file(struct repository *r)
 {
 	struct strbuf midx = STRBUF_INIT;
 
-	get_midx_filename(r->hash_algo, &midx, r->objects->sources->path);
+	get_midx_filename(r->objects->sources, &midx);
 
 	if (r->objects) {
 		struct odb_source *source;
@@ -834,8 +824,8 @@ void clear_midx_file(struct repository *r)
 	if (remove_path(midx.buf))
 		die(_("failed to clear multi-pack-index at %s"), midx.buf);
 
-	clear_midx_files_ext(r->objects->sources->path, MIDX_EXT_BITMAP, NULL);
-	clear_midx_files_ext(r->objects->sources->path, MIDX_EXT_REV, NULL);
+	clear_midx_files_ext(r->objects->sources, MIDX_EXT_BITMAP, NULL);
+	clear_midx_files_ext(r->objects->sources, MIDX_EXT_REV, NULL);
 
 	strbuf_release(&midx);
 }
@@ -879,12 +869,13 @@ static int compare_pair_pos_vs_id(const void *_a, const void *_b)
 			display_progress(progress, _n); \
 	} while (0)
 
-int verify_midx_file(struct repository *r, const char *object_dir, unsigned flags)
+int verify_midx_file(struct odb_source *source, unsigned flags)
 {
+	struct repository *r = source->odb->repo;
 	struct pair_pos_vs_id *pairs = NULL;
 	uint32_t i;
 	struct progress *progress = NULL;
-	struct multi_pack_index *m = load_multi_pack_index(r, object_dir, 1);
+	struct multi_pack_index *m = load_multi_pack_index(source);
 	struct multi_pack_index *curr;
 	verify_midx_error = 0;
 
@@ -893,7 +884,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 		struct stat sb;
 		struct strbuf filename = STRBUF_INIT;
 
-		get_midx_filename(r->hash_algo, &filename, object_dir);
+		get_midx_filename(source, &filename);
 
 		if (!stat(filename.buf, &sb)) {
 			error(_("multi-pack-index file exists, but failed to parse"));
@@ -911,7 +902,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 						  _("Looking for referenced packfiles"),
 						  m->num_packs + m->num_packs_in_base);
 	for (i = 0; i < m->num_packs + m->num_packs_in_base; i++) {
-		if (prepare_midx_pack(r, m, i))
+		if (prepare_midx_pack(m, i))
 			midx_report("failed to load pack in position %d", i);
 
 		display_progress(progress, i + 1);
@@ -988,7 +979,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 
 		nth_midxed_object_oid(&oid, m, pairs[i].pos);
 
-		if (!fill_midx_entry(r, &oid, &e, m)) {
+		if (!fill_midx_entry(m, &oid, &e)) {
 			midx_report(_("failed to load pack entry for oid[%d] = %s"),
 				    pairs[i].pos, oid_to_hex(&oid));
 			continue;
diff --git a/midx.h b/midx.h
index 076382de8a..e241d2d690 100644
--- a/midx.h
+++ b/midx.h
@@ -35,6 +35,8 @@ struct odb_source;
 	"GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL"
 
 struct multi_pack_index {
+	struct odb_source *source;
+
 	const unsigned char *data;
 	size_t data_len;
 
@@ -50,7 +52,6 @@ struct multi_pack_index {
 	uint32_t num_objects;
 	int preferred_pack_idx;
 
-	int local;
 	int has_chain;
 
 	const unsigned char *chunk_pack_names;
@@ -71,10 +72,6 @@ struct multi_pack_index {
 
 	const char **pack_names;
 	struct packed_git **packs;
-
-	struct repository *repo;
-
-	char object_dir[FLEX_ARRAY];
 };
 
 #define MIDX_PROGRESS     (1 << 0)
@@ -89,24 +86,19 @@ struct multi_pack_index {
 #define MIDX_EXT_MIDX "midx"
 
 const unsigned char *get_midx_checksum(struct multi_pack_index *m);
-void get_midx_filename(const struct git_hash_algo *hash_algo,
-		       struct strbuf *out, const char *object_dir);
-void get_midx_filename_ext(const struct git_hash_algo *hash_algo,
-			   struct strbuf *out, const char *object_dir,
+void get_midx_filename(struct odb_source *source, struct strbuf *out);
+void get_midx_filename_ext(struct odb_source *source, struct strbuf *out,
 			   const unsigned char *hash, const char *ext);
-void get_midx_chain_dirname(struct strbuf *buf, const char *object_dir);
-void get_midx_chain_filename(struct strbuf *buf, const char *object_dir);
-void get_split_midx_filename_ext(const struct git_hash_algo *hash_algo,
-				 struct strbuf *buf, const char *object_dir,
+void get_midx_chain_dirname(struct odb_source *source, struct strbuf *out);
+void get_midx_chain_filename(struct odb_source *source, struct strbuf *out);
+void get_split_midx_filename_ext(struct odb_source *source, struct strbuf *buf,
 				 const unsigned char *hash, const char *ext);
 
-struct multi_pack_index *load_multi_pack_index(struct repository *r,
-					       const char *object_dir,
-					       int local);
-int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
+struct multi_pack_index *load_multi_pack_index(struct odb_source *source);
+int prepare_midx_pack(struct multi_pack_index *m, uint32_t pack_int_id);
 struct packed_git *nth_midxed_pack(struct multi_pack_index *m,
 				   uint32_t pack_int_id);
-int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
+int nth_bitmapped_pack(struct multi_pack_index *m,
 		       struct bitmapped_pack *bp, uint32_t pack_int_id);
 int bsearch_one_midx(const struct object_id *oid, struct multi_pack_index *m,
 		     uint32_t *result);
@@ -118,27 +110,27 @@ uint32_t nth_midxed_pack_int_id(struct multi_pack_index *m, uint32_t pos);
 struct object_id *nth_midxed_object_oid(struct object_id *oid,
 					struct multi_pack_index *m,
 					uint32_t n);
-int fill_midx_entry(struct repository *r, const struct object_id *oid, struct pack_entry *e, struct multi_pack_index *m);
+int fill_midx_entry(struct multi_pack_index *m, const struct object_id *oid, struct pack_entry *e);
 int midx_contains_pack(struct multi_pack_index *m,
 		       const char *idx_or_pack_name);
 int midx_preferred_pack(struct multi_pack_index *m, uint32_t *pack_int_id);
-int prepare_multi_pack_index_one(struct odb_source *source, int local);
+int prepare_multi_pack_index_one(struct odb_source *source);
 
 /*
  * Variant of write_midx_file which writes a MIDX containing only the packs
  * specified in packs_to_include.
  */
-int write_midx_file(struct repository *r, const char *object_dir,
+int write_midx_file(struct odb_source *source,
 		    const char *preferred_pack_name, const char *refs_snapshot,
 		    unsigned flags);
-int write_midx_file_only(struct repository *r, const char *object_dir,
+int write_midx_file_only(struct odb_source *source,
 			 struct string_list *packs_to_include,
 			 const char *preferred_pack_name,
 			 const char *refs_snapshot, unsigned flags);
 void clear_midx_file(struct repository *r);
-int verify_midx_file(struct repository *r, const char *object_dir, unsigned flags);
-int expire_midx_packs(struct repository *r, const char *object_dir, unsigned flags);
-int midx_repack(struct repository *r, const char *object_dir, size_t batch_size, unsigned flags);
+int verify_midx_file(struct odb_source *source, unsigned flags);
+int expire_midx_packs(struct odb_source *source, unsigned flags);
+int midx_repack(struct odb_source *source, size_t batch_size, unsigned flags);
 
 void close_midx(struct multi_pack_index *m);
 
diff --git a/odb.c b/odb.c
index 2a92a018c4..75c443fe66 100644
--- a/odb.c
+++ b/odb.c
@@ -139,23 +139,21 @@ static void read_info_alternates(struct object_database *odb,
 				 const char *relative_base,
 				 int depth);
 
-static int link_alt_odb_entry(struct object_database *odb,
-			      const struct strbuf *entry,
-			      const char *relative_base,
-			      int depth,
-			      const char *normalized_objdir)
+static struct odb_source *link_alt_odb_entry(struct object_database *odb,
+					     const char *dir,
+					     const char *relative_base,
+					     int depth)
 {
-	struct odb_source *alternate;
+	struct odb_source *alternate = NULL;
 	struct strbuf pathbuf = STRBUF_INIT;
 	struct strbuf tmp = STRBUF_INIT;
 	khiter_t pos;
-	int ret = -1;
 
-	if (!is_absolute_path(entry->buf) && relative_base) {
+	if (!is_absolute_path(dir) && relative_base) {
 		strbuf_realpath(&pathbuf, relative_base, 1);
 		strbuf_addch(&pathbuf, '/');
 	}
-	strbuf_addbuf(&pathbuf, entry);
+	strbuf_addstr(&pathbuf, dir);
 
 	if (!strbuf_realpath(&tmp, pathbuf.buf, 0)) {
 		error(_("unable to normalize alternate object path: %s"),
@@ -171,11 +169,15 @@ static int link_alt_odb_entry(struct object_database *odb,
 	while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
 		strbuf_setlen(&pathbuf, pathbuf.len - 1);
 
-	if (!alt_odb_usable(odb, &pathbuf, normalized_objdir, &pos))
+	strbuf_reset(&tmp);
+	strbuf_realpath(&tmp, odb->sources->path, 1);
+
+	if (!alt_odb_usable(odb, &pathbuf, tmp.buf, &pos))
 		goto error;
 
 	CALLOC_ARRAY(alternate, 1);
 	alternate->odb = odb;
+	alternate->local = false;
 	/* pathbuf.buf is already in r->objects->source_by_path */
 	alternate->path = strbuf_detach(&pathbuf, NULL);
 
@@ -188,11 +190,11 @@ static int link_alt_odb_entry(struct object_database *odb,
 
 	/* recursively add alternates */
 	read_info_alternates(odb, alternate->path, depth + 1);
-	ret = 0;
+
  error:
 	strbuf_release(&tmp);
 	strbuf_release(&pathbuf);
-	return ret;
+	return alternate;
 }
 
 static const char *parse_alt_odb_entry(const char *string,
@@ -227,8 +229,7 @@ static const char *parse_alt_odb_entry(const char *string,
 static void link_alt_odb_entries(struct object_database *odb, const char *alt,
 				 int sep, const char *relative_base, int depth)
 {
-	struct strbuf objdirbuf = STRBUF_INIT;
-	struct strbuf entry = STRBUF_INIT;
+	struct strbuf dir = STRBUF_INIT;
 
 	if (!alt || !*alt)
 		return;
@@ -239,17 +240,13 @@ static void link_alt_odb_entries(struct object_database *odb, const char *alt,
 		return;
 	}
 
-	strbuf_realpath(&objdirbuf, odb->sources->path, 1);
-
 	while (*alt) {
-		alt = parse_alt_odb_entry(alt, sep, &entry);
-		if (!entry.len)
+		alt = parse_alt_odb_entry(alt, sep, &dir);
+		if (!dir.len)
 			continue;
-		link_alt_odb_entry(odb, &entry,
-				   relative_base, depth, objdirbuf.buf);
+		link_alt_odb_entry(odb, dir.buf, relative_base, depth);
 	}
-	strbuf_release(&entry);
-	strbuf_release(&objdirbuf);
+	strbuf_release(&dir);
 }
 
 static void read_info_alternates(struct object_database *odb,
@@ -272,7 +269,7 @@ static void read_info_alternates(struct object_database *odb,
 }
 
 void odb_add_to_alternates_file(struct object_database *odb,
-				const char *reference)
+				const char *dir)
 {
 	struct lock_file lock = LOCK_INIT;
 	char *alts = repo_git_path(odb->repo, "objects/info/alternates");
@@ -289,7 +286,7 @@ void odb_add_to_alternates_file(struct object_database *odb,
 		struct strbuf line = STRBUF_INIT;
 
 		while (strbuf_getline(&line, in) != EOF) {
-			if (!strcmp(reference, line.buf)) {
+			if (!strcmp(dir, line.buf)) {
 				found = 1;
 				break;
 			}
@@ -305,27 +302,24 @@ void odb_add_to_alternates_file(struct object_database *odb,
 	if (found) {
 		rollback_lock_file(&lock);
 	} else {
-		fprintf_or_die(out, "%s\n", reference);
+		fprintf_or_die(out, "%s\n", dir);
 		if (commit_lock_file(&lock))
 			die_errno(_("unable to move new alternates file into place"));
 		if (odb->loaded_alternates)
-			link_alt_odb_entries(odb, reference,
-					     '\n', NULL, 0);
+			link_alt_odb_entries(odb, dir, '\n', NULL, 0);
 	}
 	free(alts);
 }
 
-void odb_add_to_alternates_memory(struct object_database *odb,
-				  const char *reference)
+struct odb_source *odb_add_to_alternates_memory(struct object_database *odb,
+						const char *dir)
 {
 	/*
 	 * Make sure alternates are initialized, or else our entry may be
 	 * overwritten when they are.
 	 */
 	odb_prepare_alternates(odb);
-
-	link_alt_odb_entries(odb, reference,
-			     '\n', NULL, 0);
+	return link_alt_odb_entry(odb, dir, NULL, 0);
 }
 
 struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
@@ -463,6 +457,12 @@ struct odb_source *odb_find_source(struct object_database *odb, const char *obj_
 	free(obj_dir_real);
 	strbuf_release(&odb_path_real);
 
+	return source;
+}
+
+struct odb_source *odb_find_source_or_die(struct object_database *odb, const char *obj_dir)
+{
+	struct odb_source *source = odb_find_source(odb, obj_dir);
 	if (!source)
 		die(_("could not find object directory matching %s"), obj_dir);
 	return source;
diff --git a/odb.h b/odb.h
index 3dfc66d75a..51fe8a5a92 100644
--- a/odb.h
+++ b/odb.h
@@ -64,6 +64,14 @@ struct odb_source {
 	struct multi_pack_index *midx;
 
 	/*
+	 * Figure out whether this is the local source of the owning
+	 * repository, which would typically be its ".git/objects" directory.
+	 * This local object directory is usually where objects would be
+	 * written to.
+	 */
+	bool local;
+
+	/*
 	 * This is a temporary object store created by the tmp_objdir
 	 * facility. Disable ref updates since the objects in the store
 	 * might be discarded on rollback.
@@ -178,11 +186,14 @@ struct object_database *odb_new(struct repository *repo);
 void odb_clear(struct object_database *o);
 
 /*
- * Find source by its object directory path. Dies in case the source couldn't
- * be found.
+ * Find source by its object directory path. Returns a `NULL` pointer in case
+ * the source could not be found.
  */
 struct odb_source *odb_find_source(struct object_database *odb, const char *obj_dir);
 
+/* Same as `odb_find_source()`, but dies in case the source doesn't exist. */
+struct odb_source *odb_find_source_or_die(struct object_database *odb, const char *obj_dir);
+
 /*
  * Replace the current writable object directory with the specified temporary
  * object directory; returns the former primary source.
@@ -257,8 +268,8 @@ void odb_add_to_alternates_file(struct object_database *odb,
  * recursive alternates it points to), but do not modify the on-disk alternates
  * file.
  */
-void odb_add_to_alternates_memory(struct object_database *odb,
-				  const char *dir);
+struct odb_source *odb_add_to_alternates_memory(struct object_database *odb,
+						const char *dir);
 
 /*
  * Read an object from the database. Returns the object data and assigns object
diff --git a/pack-bitmap.c b/pack-bitmap.c
index d14421ee20..058bdb5d7d 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -216,7 +216,7 @@ static uint32_t bitmap_num_objects(struct bitmap_index *index)
 static struct repository *bitmap_repo(struct bitmap_index *bitmap_git)
 {
 	if (bitmap_is_midx(bitmap_git))
-		return bitmap_git->midx->repo;
+		return bitmap_git->midx->source->odb->repo;
 	return bitmap_git->pack->repo;
 }
 
@@ -418,13 +418,12 @@ char *midx_bitmap_filename(struct multi_pack_index *midx)
 {
 	struct strbuf buf = STRBUF_INIT;
 	if (midx->has_chain)
-		get_split_midx_filename_ext(midx->repo->hash_algo, &buf,
-					    midx->object_dir,
+		get_split_midx_filename_ext(midx->source, &buf,
 					    get_midx_checksum(midx),
 					    MIDX_EXT_BITMAP);
 	else
-		get_midx_filename_ext(midx->repo->hash_algo, &buf,
-				      midx->object_dir, get_midx_checksum(midx),
+		get_midx_filename_ext(midx->source, &buf,
+				      get_midx_checksum(midx),
 				      MIDX_EXT_BITMAP);
 
 	return strbuf_detach(&buf, NULL);
@@ -463,7 +462,7 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 
 	if (bitmap_git->pack || bitmap_git->midx) {
 		struct strbuf buf = STRBUF_INIT;
-		get_midx_filename(midx->repo->hash_algo, &buf, midx->object_dir);
+		get_midx_filename(midx->source, &buf);
 		trace2_data_string("bitmap", bitmap_repo(bitmap_git),
 				   "ignoring extra midx bitmap file", buf.buf);
 		close(fd);
@@ -493,7 +492,7 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	}
 
 	for (i = 0; i < bitmap_git->midx->num_packs + bitmap_git->midx->num_packs_in_base; i++) {
-		if (prepare_midx_pack(bitmap_repo(bitmap_git), bitmap_git->midx, i)) {
+		if (prepare_midx_pack(bitmap_git->midx, i)) {
 			warning(_("could not open pack %s"),
 				bitmap_git->midx->pack_names[i]);
 			goto cleanup;
@@ -2466,7 +2465,7 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 		struct multi_pack_index *m = bitmap_git->midx;
 		for (i = 0; i < m->num_packs + m->num_packs_in_base; i++) {
 			struct bitmapped_pack pack;
-			if (nth_bitmapped_pack(r, bitmap_git->midx, &pack, i) < 0) {
+			if (nth_bitmapped_pack(bitmap_git->midx, &pack, i) < 0) {
 				warning(_("unable to load pack: '%s', disabling pack-reuse"),
 					bitmap_git->midx->pack_names[i]);
 				free(packs);
diff --git a/pack-revindex.c b/pack-revindex.c
index 0cc422a1e6..d0791cc493 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -379,25 +379,25 @@ int load_midx_revindex(struct multi_pack_index *m)
 		 * not want to accidentally call munmap() in the middle of the
 		 * MIDX.
 		 */
-		trace2_data_string("load_midx_revindex", m->repo,
+		trace2_data_string("load_midx_revindex", m->source->odb->repo,
 				   "source", "midx");
 		m->revindex_data = (const uint32_t *)m->chunk_revindex;
 		return 0;
 	}
 
-	trace2_data_string("load_midx_revindex", m->repo,
+	trace2_data_string("load_midx_revindex", m->source->odb->repo,
 			   "source", "rev");
 
 	if (m->has_chain)
-		get_split_midx_filename_ext(m->repo->hash_algo, &revindex_name,
-					    m->object_dir, get_midx_checksum(m),
+		get_split_midx_filename_ext(m->source, &revindex_name,
+					    get_midx_checksum(m),
 					    MIDX_EXT_REV);
 	else
-		get_midx_filename_ext(m->repo->hash_algo, &revindex_name,
-				      m->object_dir, get_midx_checksum(m),
+		get_midx_filename_ext(m->source, &revindex_name,
+				      get_midx_checksum(m),
 				      MIDX_EXT_REV);
 
-	ret = load_revindex_from_disk(m->repo->hash_algo,
+	ret = load_revindex_from_disk(m->source->odb->repo->hash_algo,
 				      revindex_name.buf,
 				      m->num_objects,
 				      &m->revindex_map,
diff --git a/packfile.c b/packfile.c
index 5d73932f50..acb680966d 100644
--- a/packfile.c
+++ b/packfile.c
@@ -935,14 +935,14 @@ static void prepare_pack(const char *full_name, size_t full_name_len,
 		report_garbage(PACKDIR_FILE_GARBAGE, full_name);
 }
 
-static void prepare_packed_git_one(struct odb_source *source, int local)
+static void prepare_packed_git_one(struct odb_source *source)
 {
 	struct string_list garbage = STRING_LIST_INIT_DUP;
 	struct prepare_pack_data data = {
 		.m = source->midx,
 		.r = source->odb->repo,
 		.garbage = &garbage,
-		.local = local,
+		.local = source->local,
 	};
 
 	for_each_file_in_pack_dir(source->path, prepare_pack, &data);
@@ -1037,9 +1037,8 @@ static void prepare_packed_git(struct repository *r)
 
 	odb_prepare_alternates(r->objects);
 	for (source = r->objects->sources; source; source = source->next) {
-		int local = (source == r->objects->sources);
-		prepare_multi_pack_index_one(source, local);
-		prepare_packed_git_one(source, local);
+		prepare_multi_pack_index_one(source);
+		prepare_packed_git_one(source);
 	}
 	rearrange_packed_git(r);
 
@@ -1092,7 +1091,7 @@ struct packed_git *get_all_packs(struct repository *r)
 		if (!m)
 			continue;
 		for (uint32_t i = 0; i < m->num_packs + m->num_packs_in_base; i++)
-			prepare_midx_pack(r, m, i);
+			prepare_midx_pack(m, i);
 	}
 
 	return r->objects->packed_git;
@@ -2078,7 +2077,7 @@ int find_pack_entry(struct repository *r, const struct object_id *oid, struct pa
 	prepare_packed_git(r);
 
 	for (struct odb_source *source = r->objects->sources; source; source = source->next)
-		if (source->midx && fill_midx_entry(r, oid, e, source->midx))
+		if (source->midx && fill_midx_entry(source->midx, oid, e))
 			return 1;
 
 	if (!r->objects->packed_git)
diff --git a/repository.c b/repository.c
index ecd691181f..97f0578381 100644
--- a/repository.c
+++ b/repository.c
@@ -168,6 +168,7 @@ void repo_set_gitdir(struct repository *repo,
 	if (!repo->objects->sources) {
 		CALLOC_ARRAY(repo->objects->sources, 1);
 		repo->objects->sources->odb = repo->objects;
+		repo->objects->sources->local = true;
 		repo->objects->sources_tail = &repo->objects->sources->next;
 	}
 	expand_base_dir(&repo->objects->sources->path, o->object_dir,
diff --git a/t/helper/test-read-midx.c b/t/helper/test-read-midx.c
index da2aa036b5..6de5d1665a 100644
--- a/t/helper/test-read-midx.c
+++ b/t/helper/test-read-midx.c
@@ -11,14 +11,24 @@
 #include "gettext.h"
 #include "pack-revindex.h"
 
+static struct multi_pack_index *setup_midx(const char *object_dir)
+{
+	struct odb_source *source;
+	setup_git_directory();
+	source = odb_find_source(the_repository->objects, object_dir);
+	if (!source)
+		source = odb_add_to_alternates_memory(the_repository->objects,
+						      object_dir);
+	return load_multi_pack_index(source);
+}
+
 static int read_midx_file(const char *object_dir, const char *checksum,
 			  int show_objects)
 {
 	uint32_t i;
 	struct multi_pack_index *m;
 
-	setup_git_directory();
-	m = load_multi_pack_index(the_repository, object_dir, 1);
+	m = setup_midx(object_dir);
 
 	if (!m)
 		return 1;
@@ -56,7 +66,7 @@ static int read_midx_file(const char *object_dir, const char *checksum,
 	for (i = 0; i < m->num_packs; i++)
 		printf("%s\n", m->pack_names[i]);
 
-	printf("object-dir: %s\n", m->object_dir);
+	printf("object-dir: %s\n", m->source->path);
 
 	if (show_objects) {
 		struct object_id oid;
@@ -65,7 +75,7 @@ static int read_midx_file(const char *object_dir, const char *checksum,
 		for (i = 0; i < m->num_objects; i++) {
 			nth_midxed_object_oid(&oid, m,
 					      i + m->num_objects_in_base);
-			fill_midx_entry(the_repository, &oid, &e, m);
+			fill_midx_entry(m, &oid, &e);
 
 			printf("%s %"PRIu64"\t%s\n",
 			       oid_to_hex(&oid), e.offset, e.p->pack_name);
@@ -81,8 +91,7 @@ static int read_midx_checksum(const char *object_dir)
 {
 	struct multi_pack_index *m;
 
-	setup_git_directory();
-	m = load_multi_pack_index(the_repository, object_dir, 1);
+	m = setup_midx(object_dir);
 	if (!m)
 		return 1;
 	printf("%s\n", hash_to_hex(get_midx_checksum(m)));
@@ -96,9 +105,7 @@ static int read_midx_preferred_pack(const char *object_dir)
 	struct multi_pack_index *midx = NULL;
 	uint32_t preferred_pack;
 
-	setup_git_directory();
-
-	midx = load_multi_pack_index(the_repository, object_dir, 1);
+	midx = setup_midx(object_dir);
 	if (!midx)
 		return 1;
 
@@ -119,14 +126,12 @@ static int read_midx_bitmapped_packs(const char *object_dir)
 	struct bitmapped_pack pack;
 	uint32_t i;
 
-	setup_git_directory();
-
-	midx = load_multi_pack_index(the_repository, object_dir, 1);
+	midx = setup_midx(object_dir);
 	if (!midx)
 		return 1;
 
 	for (i = 0; i < midx->num_packs + midx->num_packs_in_base; i++) {
-		if (nth_bitmapped_pack(the_repository, midx, &pack, i) < 0) {
+		if (nth_bitmapped_pack(midx, &pack, i) < 0) {
 			close_midx(midx);
 			return 1;
 		}
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index bd75dea950..4e5e882989 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -28,11 +28,11 @@ midx_read_expect () {
 		EOF
 		if test $NUM_PACKS -ge 1
 		then
-			ls $OBJECT_DIR/pack/ | grep idx | sort
+			ls "$OBJECT_DIR"/pack/ | grep idx | sort
 		fi &&
 		printf "object-dir: $OBJECT_DIR\n"
 	} >expect &&
-	test-tool read-midx $OBJECT_DIR >actual &&
+	test-tool read-midx "$OBJECT_DIR" >actual &&
 	test_cmp expect actual
 }
 
@@ -305,7 +305,7 @@ test_expect_success 'midx picks objects from preferred pack' '
 
 		ofs=$(git show-index <objects/pack/test-BC-$bc.idx | grep $b |
 			cut -d" " -f1) &&
-		printf "%s %s\tobjects/pack/test-BC-%s.pack\n" \
+		printf "%s %s\t./objects/pack/test-BC-%s.pack\n" \
 			"$b" "$ofs" "$bc" >expect &&
 		grep ^$b out >actual &&
 
@@ -639,7 +639,7 @@ test_expect_success 'force some 64-bit offsets with pack-objects' '
 		( cd ../objects64 && pwd ) >.git/objects/info/alternates &&
 		midx64=$(git multi-pack-index --object-dir=../objects64 write)
 	) &&
-	midx_read_expect 1 63 5 objects64 " large-offsets"
+	midx_read_expect 1 63 5 "$(pwd)/objects64" " large-offsets"
 '
 
 test_expect_success 'verify multi-pack-index with 64-bit offsets' '