Merge branch 'ps/odb-files-alternates'

The odb_source API has been refactored to make alternates an
implementation detail of the files backend instead of managing them
at the core object database layer.

* ps/odb-files-alternates:
  odb/source: drop `read_alternates` callback
  odb/source-files: move alternates into the backend
  odb/source-files: extract reading alternates
  odb/source: make `will_destroy` an implementation detail
  tmp-objdir: replace primary source at creation time
  tmp-objdir: manage quarantine as an object directory
  tmp-objdir: absorb logic to set and restore primary sources
  odb/source-files: add the ability to have multiple object dirs
  odb: refactor `odb_find_source()` to yield dirs
  odb: refactor `odb_for_each_alternate()` to yield dirs
  odb/source-files: introduce `struct odb_files_dir`
  commit-graph: stop depending on `struct odb_source`
  commit-graph: require resolved packfile paths for `stdin_packs`

builtin/commit-graph.c

@@ -8,6 +8,8 @@
 #include "parse-options.h"
 #include "commit-graph.h"
 #include "odb.h"
+#include "odb/source.h"
+#include "odb/source-files.h"
 #include "progress.h"
 #include "replace-object.h"
 #include "strbuf.h"
@@ -67,7 +69,7 @@ static int graph_verify(int argc, const char **argv, const char *prefix,
 			struct repository *repo UNUSED)
 {
 	struct commit_graph *graph = NULL;
-	struct odb_source *source = NULL;
+	struct odb_files_dir *dir = NULL;
 	char *graph_name;
 	char *chain_name;
 	enum { OPENED_NONE, OPENED_GRAPH, OPENED_CHAIN } opened = OPENED_NONE;
@@ -102,9 +104,12 @@ static int graph_verify(int argc, const char **argv, const char *prefix,
 	if (opts.progress)
 		flags |= COMMIT_GRAPH_WRITE_PROGRESS;
 
-	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);
+	dir = odb_source_files_find_dir(the_repository->objects, opts.obj_dir);
+	if (!dir)
+		die(_("could not find object directory matching %s"), opts.obj_dir);
+
+	graph_name = get_commit_graph_filename(dir->abspath);
+	chain_name = get_commit_graph_chain_filename(dir->abspath);
 	if (open_commit_graph(graph_name, &fd, &st))
 		opened = OPENED_GRAPH;
 	else if (errno != ENOENT)
@@ -122,7 +127,7 @@ static int graph_verify(int argc, const char **argv, const char *prefix,
 	if (opened == OPENED_NONE)
 		return 0;
 	else if (opened == OPENED_GRAPH)
-		graph = load_commit_graph_one_fd_st(source, fd, &st);
+		graph = load_commit_graph_one_fd_st(the_repository, dir->abspath, fd, &st);
 	else
 		graph = load_commit_graph_chain_fd_st(the_repository->objects, fd, &st,
 						      &incomplete_chain);
@@ -225,7 +230,7 @@ static int graph_write(int argc, const char **argv, const char *prefix,
 	struct string_list pack_indexes = STRING_LIST_INIT_DUP;
 	struct strbuf buf = STRBUF_INIT;
 	struct oidset commits = OIDSET_INIT;
-	struct odb_source *source = NULL;
+	struct odb_files_dir *dir = NULL;
 	int result = 0;
 	enum commit_graph_write_flags flags = 0;
 	struct progress *progress = NULL;
@@ -293,18 +298,30 @@ 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_or_die(the_repository->objects, opts.obj_dir);
+	dir = odb_source_files_find_dir(the_repository->objects, opts.obj_dir);
+	if (!dir)
+		die(_("could not find object directory matching %s"), opts.obj_dir);
 
 	if (opts.reachable) {
-		if (write_commit_graph_reachable(source, flags, &write_opts))
+		if (write_commit_graph_reachable(the_repository, dir->abspath, flags, &write_opts))
 			result = 1;
 		goto cleanup;
 	}
 
 	if (opts.stdin_packs) {
-		while (strbuf_getline(&buf, stdin) != EOF)
-			string_list_append_nodup(&pack_indexes,
-						 strbuf_detach(&buf, NULL));
+		struct strbuf packname = STRBUF_INIT;
+		size_t dirlen;
+
+		strbuf_addf(&packname, "%s/pack/", dir->abspath);
+		dirlen = packname.len;
+
+		while (strbuf_getline(&buf, stdin) != EOF) {
+			strbuf_setlen(&packname, dirlen);
+			strbuf_addbuf(&packname, &buf);
+			string_list_append(&pack_indexes, packname.buf);
+		}
+
+		strbuf_release(&packname);
 	} else if (opts.stdin_commits) {
 		oidset_init(&commits, 0);
 		if (opts.progress)
@@ -323,7 +340,7 @@ static int graph_write(int argc, const char **argv, const char *prefix,
 		stop_progress(&progress);
 	}
 
-	if (write_commit_graph(source,
+	if (write_commit_graph(the_repository, dir->abspath,
 			       opts.stdin_packs ? &pack_indexes : NULL,
 			       opts.stdin_commits ? &commits : NULL,
 			       flags,

builtin/commit.c

@@ -1959,7 +1959,7 @@ int cmd_commit(int argc,
 		      "new index file. Check that disk is not full and quota is\n"
 		      "not exceeded, and then \"git restore --staged :/\" to recover."));
 
-	git_test_write_commit_graph_or_die(the_repository->objects->sources);
+	git_test_write_commit_graph_or_die(the_repository);
 
 	repo_rerere(the_repository, 0);
 	run_auto_maintenance(the_repository, quiet);

builtin/count-objects.c

@@ -81,10 +81,10 @@ static int count_cruft(const char *basename UNUSED, const char *path,
 	return 0;
 }
 
-static int print_alternate(struct odb_source *alternate, void *data UNUSED)
+static int print_alternate(struct odb_files_dir *alternate, void *data UNUSED)
 {
 	printf("alternate: ");
-	quote_c_style(alternate->path, NULL, stdout, 0);
+	quote_c_style(alternate->abspath, NULL, stdout, 0);
 	putchar('\n');
 	return 0;
 }
@@ -118,7 +118,7 @@ int cmd_count_objects(int argc,
 		report_linked_checkout_garbage(the_repository);
 	}
 
-	for_each_loose_file_in_source(the_repository->objects->sources,
+	for_each_loose_file_in_source(the_repository->objects->source,
 				      count_loose, count_cruft, NULL, NULL);
 
 	if (verbose) {

builtin/fast-import.c

@@ -895,7 +895,7 @@ static void end_packfile(void)
 	running = 1;
 	clear_delta_base_cache();
 	if (object_count) {
-		struct odb_source_files *files = odb_source_files_downcast(pack_data->repo->objects->sources);
+		struct odb_source_files *files = odb_source_files_downcast(pack_data->repo->objects->source);
 		struct packed_git *new_p;
 		struct object_id cur_pack_oid;
 		char *idx_name;
@@ -921,7 +921,7 @@ static void end_packfile(void)
 		idx_name = keep_pack(create_index());
 
 		/* Register the packfile with core git's machinery. */
-		new_p = packfile_store_load_pack(files->packed, idx_name, 1);
+		new_p = packfile_store_load_pack(files->dirs->packed, idx_name, 1);
 		if (!new_p)
 			die(_("core Git rejected index %s"), idx_name);
 		all_packs[pack_id] = new_p;
@@ -975,7 +975,7 @@ static int store_object(
 	struct object_id *oidout,
 	uintmax_t mark)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 	void *out, *delta;
 	struct object_entry *e;
 	unsigned char hdr[96];
@@ -1002,10 +1002,8 @@ static int store_object(
 		return 1;
 	}
 
-	for (source = the_repository->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		if (!packfile_list_find_oid(packfile_store_get_packs(files->packed), &oid))
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!packfile_list_find_oid(packfile_store_get_packs(dir->packed), &oid))
 			continue;
 		e->type = type;
 		e->pack_id = MAX_PACK_ID;
@@ -1125,10 +1123,10 @@ static void truncate_pack(struct hashfile_checkpoint *checkpoint)
 
 static void stream_blob(uintmax_t len, struct object_id *oidout, uintmax_t mark)
 {
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 	size_t in_sz = 64 * 1024, out_sz = 64 * 1024;
 	unsigned char *in_buf = xmalloc(in_sz);
 	unsigned char *out_buf = xmalloc(out_sz);
-	struct odb_source *source;
 	struct object_entry *e;
 	struct object_id oid;
 	unsigned long hdrlen;
@@ -1212,10 +1210,8 @@ static void stream_blob(uintmax_t len, struct object_id *oidout, uintmax_t mark)
 		goto out;
 	}
 
-	for (source = the_repository->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		if (!packfile_list_find_oid(packfile_store_get_packs(files->packed), &oid))
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!packfile_list_find_oid(packfile_store_get_packs(dir->packed), &oid))
 			continue;
 		e->type = OBJ_BLOB;
 		e->pack_id = MAX_PACK_ID;

builtin/fetch.c

@@ -15,6 +15,7 @@
 #include "refspec.h"
 #include "object-name.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "oidset.h"
 #include "oid-array.h"
 #include "commit.h"
@@ -2944,12 +2945,14 @@ int cmd_fetch(int argc,
 					    the_repository);
 			if (graph_write_mode == GRAPH_WRITE_TIPS)
 				write_commit_graph(
-					the_repository->objects->sources,
+					the_repository,
+					the_repository->objects->source->path,
 					NULL, &updated_tips,
 					commit_graph_flags, NULL);
 			else
 				write_commit_graph_reachable(
-					the_repository->objects->sources,
+					the_repository,
+					the_repository->objects->source->path,
 					commit_graph_flags, NULL);
 			trace2_region_leave("fetch", "write-commit-graph",
 					    the_repository);

builtin/fsck.c

@@ -868,7 +868,6 @@ int cmd_fsck(int argc,
 		OPT_BOOL(0, "references", &check_references, N_("check reference database consistency")),
 		OPT_END(),
 	};
-	struct odb_source *source;
 	struct snapshot snap = {
 		.nr = 0,
 		.alloc = 0,
@@ -983,13 +982,14 @@ int cmd_fsck(int argc,
 	check_connectivity(repo);
 
 	if (repo->settings.core_commit_graph) {
+		struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
 		struct child_process commit_graph_verify = CHILD_PROCESS_INIT;
 
-		for (source = repo->objects->sources; source; source = source->next) {
+		for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
 			child_process_init(&commit_graph_verify);
 			commit_graph_verify.git_cmd = 1;
 			strvec_pushl(&commit_graph_verify.args, "commit-graph",
-				     "verify", "--object-dir", source->path, NULL);
+				     "verify", "--object-dir", dir->abspath, NULL);
 			if (show_progress)
 				strvec_push(&commit_graph_verify.args, "--progress");
 			else

builtin/gc.c

@@ -733,7 +733,8 @@ int cmd_gc(int argc,
 	}
 
 	if (the_repository->settings.gc_write_commit_graph == 1)
-		write_commit_graph_reachable(the_repository->objects->sources,
+		write_commit_graph_reachable(the_repository,
+					     the_repository->objects->source->path,
 					     !opts.quiet && !daemonized ? COMMIT_GRAPH_WRITE_PROGRESS : 0,
 					     NULL);
 
@@ -997,7 +998,7 @@ static int loose_object_auto_condition(struct gc_config *cfg UNUSED)
 	if (loose_object_auto_limit < 0)
 		return 1;
 
-	return for_each_loose_file_in_source(the_repository->objects->sources,
+	return for_each_loose_file_in_source(the_repository->objects->source,
 					     loose_object_count,
 					     NULL, NULL, &count);
 }
@@ -1032,7 +1033,7 @@ static int pack_loose(struct maintenance_run_opts *opts)
 	 * Do not start pack-objects process
 	 * if there are no loose objects.
 	 */
-	if (!for_each_loose_file_in_source(r->objects->sources,
+	if (!for_each_loose_file_in_source(r->objects->source,
 					   bail_on_loose,
 					   NULL, NULL, NULL))
 		return 0;
@@ -1044,7 +1045,7 @@ static int pack_loose(struct maintenance_run_opts *opts)
 		strvec_push(&pack_proc.args, "--quiet");
 	else
 		strvec_push(&pack_proc.args, "--no-quiet");
-	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->sources->path);
+	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->source->path);
 
 	pack_proc.in = -1;
 
@@ -1072,7 +1073,7 @@ static int pack_loose(struct maintenance_run_opts *opts)
 	else if (data.batch_size > 0)
 		data.batch_size--; /* Decrease for equality on limit. */
 
-	for_each_loose_file_in_source(r->objects->sources,
+	for_each_loose_file_in_source(r->objects->source,
 				      write_loose_object_to_stdin,
 				      NULL, NULL, &data);
 
@@ -1395,7 +1396,7 @@ static int maintenance_run_tasks(struct maintenance_run_opts *opts,
 	int result = 0;
 	struct lock_file lk;
 	struct repository *r = the_repository;
-	char *lock_path = xstrfmt("%s/maintenance", r->objects->sources->path);
+	char *lock_path = xstrfmt("%s/maintenance", r->objects->source->path);
 	enum auto_gc_hook_result auto_gc_hook_result = AUTO_GC_HOOK_UNDECIDED;
 
 	if (repo_hold_lock_file_for_update(r, &lk, lock_path, LOCK_NO_DEREF) < 0) {
@@ -2971,7 +2972,7 @@ static int update_background_schedule(const struct maintenance_start_opts *opts,
 	unsigned int i;
 	int result = 0;
 	struct lock_file lk;
-	char *lock_path = xstrfmt("%s/schedule", the_repository->objects->sources->path);
+	char *lock_path = xstrfmt("%s/schedule", the_repository->objects->source->path);
 
 	if (hold_lock_file_for_update(&lk, lock_path, LOCK_NO_DEREF) < 0) {
 		if (errno == EEXIST)

builtin/index-pack.c

@@ -1640,8 +1640,8 @@ static void final(const char *final_pack_name, const char *curr_pack_name,
 
 	if (do_fsck_object && startup_info->have_repository) {
 		struct odb_source_files *files =
-			odb_source_files_downcast(the_repository->objects->sources);
-		packfile_store_load_pack(files->packed, final_index_name, 0);
+			odb_source_files_downcast(the_repository->objects->source);
+		packfile_store_load_pack(files->dirs->packed, final_index_name, 0);
 	}
 
 	if (!from_stdin) {

builtin/merge.c

@@ -1863,7 +1863,7 @@ int cmd_merge(int argc,
 	if (squash) {
 		finish(head_commit, remoteheads, NULL, NULL);
 
-		git_test_write_commit_graph_or_die(the_repository->objects->sources);
+		git_test_write_commit_graph_or_die(the_repository);
 	} else
 		write_merge_state(remoteheads);
 

builtin/multi-pack-index.c

@@ -80,19 +80,19 @@ static int parse_object_dir(const struct option *opt, const char *arg,
 	char **value = opt->value;
 	free(*value);
 	if (unset)
-		*value = xstrdup(the_repository->objects->sources->path);
+		*value = xstrdup(the_repository->objects->source->path);
 	else
 		*value = real_pathdup(arg, 1);
 	return 0;
 }
 
-static struct odb_source_files *handle_object_dir_option(struct repository *repo)
+static struct odb_source_packed *handle_object_dir_option(struct repository *repo)
 {
-	struct odb_source *source = odb_find_source(repo->objects, opts.object_dir);
-	if (!source)
+	struct odb_files_dir *dir = odb_source_files_find_dir(repo->objects, opts.object_dir);
+	if (!dir)
 		die(_("object directory is not an alternate of the current repository: '%s'"),
 		    opts.object_dir);
-	return odb_source_files_downcast(source);
+	return dir->packed;
 }
 
 static struct option common_opts[] = {
@@ -169,7 +169,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 			     N_("refs snapshot for selecting bitmap commits")),
 		OPT_END(),
 	};
-	struct odb_source_files *source;
+	struct odb_source_packed *packed_source;
 	int ret;
 
 	opts.flags |= MIDX_WRITE_BITMAP_HASH_CACHE;
@@ -204,7 +204,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 				   options);
 	}
 
-	source = handle_object_dir_option(repo);
+	packed_source = handle_object_dir_option(repo);
 
 	FREE_AND_NULL(options);
 
@@ -213,7 +213,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 
 		read_packs_from_stdin(&packs);
 
-		ret = write_midx_file_only(source->packed, &packs,
+		ret = write_midx_file_only(packed_source, &packs,
 					   opts.preferred_pack,
 					   opts.refs_snapshot,
 					   opts.incremental_base, opts.flags);
@@ -225,7 +225,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 
 	}
 
-	ret = write_midx_file(source->packed, opts.preferred_pack,
+	ret = write_midx_file(packed_source, opts.preferred_pack,
 			      opts.refs_snapshot, opts.flags);
 
 	free(opts.refs_snapshot);
@@ -239,7 +239,7 @@ static int cmd_multi_pack_index_compact(int argc, const char **argv,
 	struct multi_pack_index *m, *cur;
 	struct multi_pack_index *from_midx = NULL;
 	struct multi_pack_index *to_midx = NULL;
-	struct odb_source_files *source;
+	struct odb_source_packed *packed_source;
 	int ret;
 
 	struct option *options;
@@ -280,11 +280,11 @@ static int cmd_multi_pack_index_compact(int argc, const char **argv,
 				   options);
 	}
 
-	source = handle_object_dir_option(the_repository);
+	packed_source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	m = get_multi_pack_index(source->packed);
+	m = get_multi_pack_index(packed_source);
 
 	for (cur = m; cur && !(from_midx && to_midx); cur = cur->base_midx) {
 		const char *midx_csum = midx_get_checksum_hex(cur);
@@ -307,7 +307,7 @@ static int cmd_multi_pack_index_compact(int argc, const char **argv,
 			die(_("MIDX %s must be an ancestor of %s"), argv[0], argv[1]);
 	}
 
-	ret = write_midx_file_compact(source->packed, from_midx, to_midx,
+	ret = write_midx_file_compact(packed_source, from_midx, to_midx,
 				      opts.incremental_base, opts.flags);
 
 	return ret;
@@ -321,7 +321,7 @@ static int cmd_multi_pack_index_verify(int argc, const char **argv,
 	static struct option builtin_multi_pack_index_verify_options[] = {
 		OPT_END(),
 	};
-	struct odb_source_files *source;
+	struct odb_source_packed *packed_source;
 
 	options = add_common_options(builtin_multi_pack_index_verify_options);
 
@@ -335,11 +335,11 @@ 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);
+	packed_source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return verify_midx_file(source->packed, opts.flags);
+	return verify_midx_file(packed_source, opts.flags);
 }
 
 static int cmd_multi_pack_index_expire(int argc, const char **argv,
@@ -350,7 +350,7 @@ static int cmd_multi_pack_index_expire(int argc, const char **argv,
 	static struct option builtin_multi_pack_index_expire_options[] = {
 		OPT_END(),
 	};
-	struct odb_source_files *source;
+	struct odb_source_packed *packed_source;
 
 	options = add_common_options(builtin_multi_pack_index_expire_options);
 
@@ -364,11 +364,11 @@ 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);
+	packed_source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return expire_midx_packs(source->packed, opts.flags);
+	return expire_midx_packs(packed_source, opts.flags);
 }
 
 static int cmd_multi_pack_index_repack(int argc, const char **argv,
@@ -381,7 +381,7 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 		  N_("during repack, collect pack-files of smaller size into a batch that is larger than this size")),
 		OPT_END(),
 	};
-	struct odb_source_files *source;
+	struct odb_source_packed *packed_source;
 
 	options = add_common_options(builtin_multi_pack_index_repack_options);
 
@@ -396,11 +396,11 @@ 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);
+	packed_source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return midx_repack(source->packed, (size_t)opts.batch_size, opts.flags);
+	return midx_repack(packed_source, (size_t)opts.batch_size, opts.flags);
 }
 
 int cmd_multi_pack_index(int argc,
@@ -426,8 +426,8 @@ int cmd_multi_pack_index(int argc,
 
 	if (the_repository &&
 	    the_repository->objects &&
-	    the_repository->objects->sources)
-		opts.object_dir = xstrdup(the_repository->objects->sources->path);
+	    the_repository->objects->source)
+		opts.object_dir = xstrdup(the_repository->objects->source->path);
 
 	argc = parse_options(argc, argv, prefix, options,
 			     builtin_multi_pack_index_usage, 0);

builtin/pack-objects.c

@@ -1566,11 +1566,10 @@ static int want_cruft_object_mtime(struct repository *r,
 				   const struct object_id *oid,
 				   unsigned flags, uint32_t mtime)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 
-	for (source = r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		struct packed_git **cache = packfile_store_get_kept_pack_cache(files->packed, flags);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		struct packed_git **cache = packfile_store_get_kept_pack_cache(dir->packed, flags);
 
 		for (; *cache; cache++) {
 			struct packed_git *p = *cache;
@@ -1753,21 +1752,19 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 				     off_t *found_offset,
 				     uint32_t found_mtime)
 {
+	struct odb_source_files *files =
+		odb_source_files_downcast(the_repository->objects->source);
 	int want;
 	struct packfile_list_entry *e;
-	struct odb_source *source;
 
 	if (!exclude && local) {
 		/*
-		 * Note that we start iterating at `sources->next` so that we
-		 * skip the local object source.
+		 * Note that we start iterating at `dirs->next` so that we
+		 * skip the local object directory.
 		 */
-		struct odb_source *source = the_repository->objects->sources->next;
-		for (; source; source = source->next) {
-			struct odb_source_files *files = odb_source_files_downcast(source);
-			if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0, NULL))
+		for (struct odb_files_dir *dir = files->dirs->next; dir; dir = dir->next)
+			if (!odb_source_read_object_info(&dir->loose->base, oid, NULL, 0, NULL))
 				return 0;
-		}
 	}
 
 	/*
@@ -1785,9 +1782,8 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 		*found_offset = 0;
 	}
 
-	for (source = the_repository->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		struct multi_pack_index *m = get_multi_pack_index(files->packed);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		struct multi_pack_index *m = get_multi_pack_index(dir->packed);
 		struct pack_entry e;
 
 		if (m && midx_fill_entry(m, oid, &e, NULL) == MIDX_FILL_HIT) {
@@ -1797,14 +1793,12 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 		}
 	}
 
-	for (source = the_repository->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		for (e = files->packed->packs.head; e; e = e->next) {
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		for (e = dir->packed->packs.head; e; e = e->next) {
 			struct packed_git *p = e->pack;
 			want = want_object_in_pack_one(p, oid, exclude, found_pack, found_offset, found_mtime);
 			if (!exclude && want > 0)
-				packfile_list_prepend(&files->packed->packs, p);
+				packfile_list_prepend(&dir->packed->packs, p);
 			if (want != -1)
 				return want;
 		}
@@ -4170,14 +4164,13 @@ static void add_cruft_object_entry(const struct object_id *oid, enum object_type
 		if (!want_object_in_pack_mtime(oid, 0, &pack, &offset, mtime))
 			return;
 		if (!pack && type == OBJ_BLOB) {
-			struct odb_source *source = the_repository->objects->sources;
+			struct odb_source_files *files =
+				odb_source_files_downcast(the_repository->objects->source);
 			int found = 0;
 
-			for (; !found && source; source = source->next) {
-				struct odb_source_files *files = odb_source_files_downcast(source);
-				if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0, NULL))
+			for (struct odb_files_dir *dir = files->dirs; !found && dir; dir = dir->next)
+				if (!odb_source_read_object_info(&dir->loose->base, oid, NULL, 0, NULL))
 					found = 1;
-			}
 
 			/*
 			 * If a traversed tree has a missing blob then we want
@@ -4512,7 +4505,8 @@ static int add_object_in_unpacked_pack(const struct object_id *oid,
 
 static void add_objects_in_unpacked_packs(void)
 {
-	struct odb_source *source;
+	struct odb_source_files *files =
+		odb_source_files_downcast(to_pack.repo->objects->source);
 	time_t mtime;
 	struct odb_for_each_object_options opts = {
 		.flags = ODB_FOR_EACH_OBJECT_PACK_ORDER |
@@ -4526,13 +4520,11 @@ static void add_objects_in_unpacked_packs(void)
 		.source_infop = &source_info,
 	};
 
-	for (source = to_pack.repo->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		if (!source->local)
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!dir->local)
 			continue;
 
-		if (odb_source_for_each_object(&files->packed->base, &oi,
+		if (odb_source_for_each_object(&dir->packed->base, &oi,
 					       add_object_in_unpacked_pack, NULL, &opts))
 			die(_("cannot open pack index"));
 	}
@@ -4576,7 +4568,7 @@ static int add_loose_object(const struct object_id *oid, const char *path,
  */
 static void add_unreachable_loose_objects(struct rev_info *revs)
 {
-	for_each_loose_file_in_source(the_repository->objects->sources,
+	for_each_loose_file_in_source(the_repository->objects->source,
 				      add_loose_object, NULL, NULL, revs);
 }
 
@@ -4640,11 +4632,9 @@ static int force_object_loose(struct odb_source *source,
 	size_t len;
 	int ret;
 
-	for (struct odb_source *s = source->odb->sources; s; s = s->next) {
-		struct odb_source_files *files = odb_source_files_downcast(s);
-		if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0, NULL))
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next)
+		if (!odb_source_read_object_info(&dir->loose->base, oid, NULL, 0, NULL))
 			return 0;
-	}
 
 	oi.typep = &type;
 	oi.sizep = &len;
@@ -4664,7 +4654,7 @@ static int force_object_loose(struct odb_source *source,
 		compat_oid_p = &compat_oid;
 	}
 
-	ret = odb_source_write_object(&files->loose->base, buf, len, type, oid,
+	ret = odb_source_write_object(&files->dirs->loose->base, buf, len, type, oid,
 				      compat_oid_p, mtime, 0);
 
 out:
@@ -4691,7 +4681,7 @@ static void loosen_unused_packed_objects(void)
 			if (!packlist_find(&to_pack, &oid) &&
 			    !has_sha1_pack_kept_or_nonlocal(&oid) &&
 			    !loosened_object_can_be_discarded(&oid, p->mtime)) {
-				if (force_object_loose(the_repository->objects->sources,
+				if (force_object_loose(the_repository->objects->source,
 						       &oid, &p->mtime))
 					die(_("unable to force loose object"));
 				loosened_objects_nr++;

builtin/prune.c

@@ -198,7 +198,7 @@ int cmd_prune(int argc,
 		revs.exclude_promisor_objects = 1;
 	}
 
-	for_each_loose_file_in_source(repo->objects->sources,
+	for_each_loose_file_in_source(repo->objects->source,
 				      prune_object, prune_cruft, prune_subdir, &revs);
 
 	prune_packed_objects(show_only ? PRUNE_PACKED_DRY_RUN : 0);

builtin/repack.c

@@ -617,7 +617,7 @@ int cmd_repack(int argc,
 		 * midx_has_unknown_packs() will make the decision for
 		 * us.
 		 */
-		if (!get_multi_pack_index(files->packed))
+		if (!get_multi_pack_index(files->dirs->packed))
 			midx_must_contain_cruft = 1;
 	}
 
@@ -775,7 +775,7 @@ int cmd_repack(int argc,
 
 		if (git_env_bool(GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL, 0))
 			flags |= MIDX_WRITE_INCREMENTAL;
-		write_midx_file(files->packed, NULL, NULL, flags);
+		write_midx_file(files->dirs->packed, NULL, NULL, flags);
 	}
 
 cleanup:

builtin/submodule--helper.c

@@ -30,6 +30,7 @@
 #include "object-name.h"
 #include "odb.h"
 #include "odb/source.h"
+#include "odb/source-files.h"
 #include "advice.h"
 #include "branch.h"
 #include "list-objects-filter-options.h"
@@ -1770,7 +1771,7 @@ static const char alternate_error_advice[] = N_(
 );
 
 static int add_possible_reference_from_superproject(
-		struct odb_source *alt_odb, void *sas_cb)
+		struct odb_files_dir *alt_odb, void *sas_cb)
 {
 	struct submodule_alternate_setup *sas = sas_cb;
 	size_t len;
@@ -1779,12 +1780,12 @@ static int add_possible_reference_from_superproject(
 	 * If the alternate object store is another repository, try the
 	 * standard layout with .git/(modules/<name>)+/objects
 	 */
-	if (strip_suffix(alt_odb->path, "/objects", &len)) {
+	if (strip_suffix(alt_odb->abspath, "/objects", &len)) {
 		struct repository alternate;
 		char *sm_alternate;
 		struct strbuf sb = STRBUF_INIT;
 		struct strbuf err = STRBUF_INIT;
-		strbuf_add(&sb, alt_odb->path, len);
+		strbuf_add(&sb, alt_odb->abspath, len);
 
 		if (repo_init(&alternate, sb.buf, NULL) < 0)
 			die(_("could not get a repository handle for gitdir '%s'"),

bundle.c

@@ -239,7 +239,7 @@ int verify_bundle(struct repository *r,
 		.quiet = 1,
 	};
 
-	if (!r || !r->objects || !r->objects->sources)
+	if (!r || !r->objects || !r->objects->source)
 		return error(_("need a repository to verify a bundle"));
 
 	for (i = 0; i < p->nr; i++) {

commit-graph.c

@@ -1,6 +1,7 @@
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
+#include "abspath.h"
 #include "config.h"
 #include "csum-file.h"
 #include "environment.h"
@@ -14,6 +15,7 @@
 #include "hash-lookup.h"
 #include "commit-graph.h"
 #include "odb.h"
+#include "odb/source-files.h"
 #include "oid-array.h"
 #include "path.h"
 #include "alloc.h"
@@ -28,7 +30,7 @@
 #include "tree.h"
 #include "chunk-format.h"
 
-void git_test_write_commit_graph_or_die(struct odb_source *source)
+void git_test_write_commit_graph_or_die(struct repository *repo)
 {
 	int flags = 0;
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0))
@@ -37,7 +39,7 @@ void git_test_write_commit_graph_or_die(struct odb_source *source)
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
 		flags = COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
-	if (write_commit_graph_reachable(source, flags, NULL))
+	if (write_commit_graph_reachable(repo, repo->objects->source->path, flags, NULL))
 		die("failed to write commit-graph under GIT_TEST_COMMIT_GRAPH");
 }
 
@@ -196,21 +198,21 @@ static int commit_gen_cmp(const void *va, const void *vb)
 	return 0;
 }
 
-char *get_commit_graph_filename(struct odb_source *source)
+char *get_commit_graph_filename(const char *dir)
 {
-	return xstrfmt("%s/info/commit-graph", source->path);
+	return xstrfmt("%s/info/commit-graph", dir);
 }
 
-static char *get_split_graph_filename(struct odb_source *source,
+static char *get_split_graph_filename(const char *dir,
 				      const char *oid_hex)
 {
-	return xstrfmt("%s/info/commit-graphs/graph-%s.graph", source->path,
+	return xstrfmt("%s/info/commit-graphs/graph-%s.graph", dir,
 		       oid_hex);
 }
 
-char *get_commit_graph_chain_filename(struct odb_source *source)
+char *get_commit_graph_chain_filename(const char *dir)
 {
-	return xstrfmt("%s/info/commit-graphs/commit-graph-chain", source->path);
+	return xstrfmt("%s/info/commit-graphs/commit-graph-chain", dir);
 }
 
 static struct commit_graph *alloc_commit_graph(void)
@@ -253,7 +255,8 @@ int open_commit_graph(const char *graph_file, int *fd, struct stat *st)
 	return 1;
 }
 
-struct commit_graph *load_commit_graph_one_fd_st(struct odb_source *source,
+struct commit_graph *load_commit_graph_one_fd_st(struct repository *repo,
+						 const char *dir,
 						 int fd, struct stat *st)
 {
 	void *graph_map;
@@ -262,7 +265,7 @@ struct commit_graph *load_commit_graph_one_fd_st(struct odb_source *source,
 
 	graph_size = xsize_t(st->st_size);
 
-	if (graph_size < graph_min_size(source->odb->repo->hash_algo)) {
+	if (graph_size < graph_min_size(repo->hash_algo)) {
 		close(fd);
 		error(_("commit-graph file is too small"));
 		return NULL;
@@ -270,9 +273,9 @@ struct commit_graph *load_commit_graph_one_fd_st(struct odb_source *source,
 	graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
 
-	ret = parse_commit_graph(source->odb->repo, graph_map, graph_size);
+	ret = parse_commit_graph(repo, graph_map, graph_size);
 	if (ret)
-		ret->odb_source = source;
+		ret->dir = absolute_pathdup(dir);
 	else
 		munmap(graph_map, graph_size);
 
@@ -410,6 +413,7 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 
 	graph = alloc_commit_graph();
 
+	graph->repo = r;
 	graph->hash_algo = r->hash_algo;
 	graph->num_chunks = *(unsigned char*)(data + 6);
 	graph->data = graph_map;
@@ -490,7 +494,8 @@ free_and_return:
 	return NULL;
 }
 
-static struct commit_graph *load_commit_graph_one(struct odb_source *source,
+static struct commit_graph *load_commit_graph_one(struct repository *repo,
+						  const char *dir,
 						  const char *graph_file)
 {
 	struct stat st;
@@ -501,17 +506,18 @@ static struct commit_graph *load_commit_graph_one(struct odb_source *source,
 	if (!open_ok)
 		return NULL;
 
-	g = load_commit_graph_one_fd_st(source, fd, &st);
+	g = load_commit_graph_one_fd_st(repo, dir, fd, &st);
 	if (g)
-		g->filename = xstrdup(graph_file);
+		g->filename = absolute_pathdup(graph_file);
 
 	return g;
 }
 
-static struct commit_graph *load_commit_graph_v1(struct odb_source *source)
+static struct commit_graph *load_commit_graph_v1(struct repository *repo,
+						 const char *dir)
 {
-	char *graph_name = get_commit_graph_filename(source);
-	struct commit_graph *g = load_commit_graph_one(source, graph_name);
+	char *graph_name = get_commit_graph_filename(dir);
+	struct commit_graph *g = load_commit_graph_one(repo, dir, graph_name);
 	free(graph_name);
 
 	return g;
@@ -652,7 +658,7 @@ struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
 	CALLOC_ARRAY(oids, count);
 
 	for (i = 0; i < count; i++) {
-		struct odb_source *source;
+		struct odb_source_files *files;
 
 		if (strbuf_getline_lf(&line, fp) == EOF)
 			break;
@@ -665,9 +671,11 @@ struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
 		}
 
 		valid = 0;
-		for (source = odb->sources; source; source = source->next) {
-			char *graph_name = get_split_graph_filename(source, line.buf);
-			struct commit_graph *g = load_commit_graph_one(source, graph_name);
+
+		files = odb_source_files_downcast(odb->source);
+		for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+			char *graph_name = get_split_graph_filename(dir->abspath, line.buf);
+			struct commit_graph *g = load_commit_graph_one(odb->repo, dir->abspath, graph_name);
 
 			free(graph_name);
 
@@ -700,29 +708,31 @@ struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
 	return graph_chain;
 }
 
-static struct commit_graph *load_commit_graph_chain(struct odb_source *source)
+static struct commit_graph *load_commit_graph_chain(struct repository *repo,
+						    const char *dir)
 {
-	char *chain_file = get_commit_graph_chain_filename(source);
+	char *chain_file = get_commit_graph_chain_filename(dir);
 	struct stat st;
 	int fd;
 	struct commit_graph *g = NULL;
 
-	if (open_commit_graph_chain(chain_file, &fd, &st, source->odb->repo->hash_algo)) {
+	if (open_commit_graph_chain(chain_file, &fd, &st, repo->hash_algo)) {
 		int incomplete;
 		/* ownership of fd is taken over by load function */
-		g = load_commit_graph_chain_fd_st(source->odb, fd, &st, &incomplete);
+		g = load_commit_graph_chain_fd_st(repo->objects, fd, &st, &incomplete);
 	}
 
 	free(chain_file);
 	return g;
 }
 
-struct commit_graph *read_commit_graph_one(struct odb_source *source)
+struct commit_graph *read_commit_graph_one(struct repository *repo,
+					   const char *dir)
 {
-	struct commit_graph *g = load_commit_graph_v1(source);
+	struct commit_graph *g = load_commit_graph_v1(repo, dir);
 
 	if (!g)
-		g = load_commit_graph_chain(source);
+		g = load_commit_graph_chain(repo, dir);
 
 	return g;
 }
@@ -735,7 +745,7 @@ struct commit_graph *read_commit_graph_one(struct odb_source *source)
  */
 struct commit_graph *prepare_commit_graph(struct repository *r)
 {
-	struct odb_source *source;
+	struct odb_source_files *files;
 
 	/*
 	 * Early return if there is no object database or if the commit graph is
@@ -766,8 +776,9 @@ struct commit_graph *prepare_commit_graph(struct repository *r)
 	if (!commit_graph_compatible(r))
 		return NULL;
 
-	for (source = r->objects->sources; source; source = source->next) {
-		r->objects->commit_graph = read_commit_graph_one(source);
+	files = odb_source_files_downcast(r->objects->source);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		r->objects->commit_graph = read_commit_graph_one(r, dir->abspath);
 		if (r->objects->commit_graph)
 			break;
 	}
@@ -866,7 +877,7 @@ static struct commit_list **insert_parent_or_die(struct commit_graph *g,
 		die("invalid parent position %"PRIu32, pos);
 
 	load_oid_from_graph(g, pos, &oid);
-	c = lookup_commit(g->odb_source->odb->repo, &oid);
+	c = lookup_commit(g->repo, &oid);
 	if (!c)
 		die(_("could not find commit %s"), oid_to_hex(&oid));
 	commit_graph_data_at(c)->graph_pos = pos;
@@ -1103,7 +1114,7 @@ static struct tree *load_tree_for_commit(struct commit_graph *g,
 				graph_pos - g->num_commits_in_base);
 
 	oidread(&oid, commit_data, g->hash_algo);
-	set_commit_tree(c, lookup_tree(g->odb_source->odb->repo, &oid));
+	set_commit_tree(c, lookup_tree(g->repo, &oid));
 
 	return c->maybe_tree;
 }
@@ -1126,7 +1137,7 @@ struct tree *get_commit_tree_in_graph(struct repository *r, const struct commit
 
 struct write_commit_graph_context {
 	struct repository *r;
-	struct odb_source *odb_source;
+	char *dir;
 	char *graph_name;
 	struct oid_array oids;
 	struct commit_stack commits;
@@ -1902,7 +1913,8 @@ static int add_ref_to_set(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
-int write_commit_graph_reachable(struct odb_source *source,
+int write_commit_graph_reachable(struct repository *repo,
+				 const char *dir,
 				 enum commit_graph_write_flags flags,
 				 const struct commit_graph_opts *opts)
 {
@@ -1911,20 +1923,20 @@ int write_commit_graph_reachable(struct odb_source *source,
 	int result;
 
 	memset(&data, 0, sizeof(data));
-	data.repo = source->odb->repo;
+	data.repo = repo;
 	data.commits = &commits;
 
 	if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
 		data.progress = start_delayed_progress(
-			source->odb->repo,
+			repo,
 			_("Collecting referenced commits"), 0);
 
-	refs_for_each_ref(get_main_ref_store(source->odb->repo), add_ref_to_set,
+	refs_for_each_ref(get_main_ref_store(repo), add_ref_to_set,
 			  &data);
 
 	stop_progress(&data.progress);
 
-	result = write_commit_graph(source, NULL, &commits,
+	result = write_commit_graph(repo, dir, NULL, &commits,
 				    flags, opts);
 
 	oidset_clear(&commits);
@@ -1936,12 +1948,8 @@ static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
 {
 	uint32_t i;
 	struct strbuf progress_title = STRBUF_INIT;
-	struct strbuf packname = STRBUF_INIT;
-	int dirlen;
 	int ret = 0;
 
-	strbuf_addf(&packname, "%s/pack/", ctx->odb_source->path);
-	dirlen = packname.len;
 	if (ctx->report_progress) {
 		strbuf_addf(&progress_title,
 			    Q_("Finding commits for commit graph in %"PRIuMAX" pack",
@@ -1954,15 +1962,15 @@ static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
 	}
 	for (i = 0; i < pack_indexes->nr; i++) {
 		struct packed_git *p;
-		strbuf_setlen(&packname, dirlen);
-		strbuf_addstr(&packname, pack_indexes->items[i].string);
-		p = add_packed_git(ctx->r, packname.buf, packname.len, 1);
+
+		p = add_packed_git(ctx->r, pack_indexes->items[i].string,
+				   strlen(pack_indexes->items[i].string), 1);
 		if (!p) {
-			ret = error(_("error adding pack %s"), packname.buf);
+			ret = error(_("error adding pack %s"), pack_indexes->items[i].string);
 			goto cleanup;
 		}
 		if (open_pack_index(p)) {
-			ret = error(_("error opening index for %s"), packname.buf);
+			ret = error(_("error opening index for %s"), pack_indexes->items[i].string);
 			close_pack(p);
 			free(p);
 			goto cleanup;
@@ -1976,7 +1984,6 @@ static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
 cleanup:
 	stop_progress(&ctx->progress);
 	strbuf_release(&progress_title);
-	strbuf_release(&packname);
 
 	return ret;
 }
@@ -2000,7 +2007,7 @@ static int fill_oids_from_commits(struct write_commit_graph_context *ctx,
 
 static void fill_oids_from_all_packs(struct write_commit_graph_context *ctx)
 {
-	struct odb_source *source;
+	struct odb_source_files *files;
 	enum object_type type;
 	struct odb_for_each_object_options opts = {
 		.flags = ODB_FOR_EACH_OBJECT_PACK_ORDER,
@@ -2015,9 +2022,9 @@ static void fill_oids_from_all_packs(struct write_commit_graph_context *ctx)
 			_("Finding commits for commit graph among packed objects"),
 			ctx->approx_nr_objects);
 
-	for (source = ctx->r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		odb_source_for_each_object(&files->packed->base, &oi, add_packed_commits_oi,
+	files = odb_source_files_downcast(ctx->r->objects->source);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		odb_source_for_each_object(&dir->packed->base, &oi, add_packed_commits_oi,
 					   ctx, &opts);
 	}
 
@@ -2108,10 +2115,10 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 
 		strbuf_addf(&tmp_file,
 			    "%s/info/commit-graphs/tmp_graph_XXXXXX",
-			    ctx->odb_source->path);
+			    ctx->dir);
 		ctx->graph_name = strbuf_detach(&tmp_file, NULL);
 	} else {
-		ctx->graph_name = get_commit_graph_filename(ctx->odb_source);
+		ctx->graph_name = get_commit_graph_filename(ctx->dir);
 	}
 
 	if (safe_create_leading_directories(ctx->r, ctx->graph_name)) {
@@ -2121,7 +2128,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	}
 
 	if (ctx->split) {
-		char *lock_name = get_commit_graph_chain_filename(ctx->odb_source);
+		char *lock_name = get_commit_graph_chain_filename(ctx->dir);
 
 		repo_hold_lock_file_for_update_mode(ctx->r, &lk, lock_name,
 						    LOCK_DIE_ON_ERROR, 0444);
@@ -2210,7 +2217,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 
 	if (ctx->split && ctx->base_graph_name && ctx->num_commit_graphs_after > 1) {
 		char *new_base_hash = xstrdup(oid_to_hex(&ctx->new_base_graph->oid));
-		char *new_base_name = get_split_graph_filename(ctx->new_base_graph->odb_source, new_base_hash);
+		char *new_base_name = get_split_graph_filename(ctx->new_base_graph->dir, new_base_hash);
 
 		free(ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 2]);
 		free(ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 2]);
@@ -2250,7 +2257,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 				}
 			}
 		} else {
-			char *graph_name = get_commit_graph_filename(ctx->odb_source);
+			char *graph_name = get_commit_graph_filename(ctx->dir);
 			unlink(graph_name);
 			free(graph_name);
 		}
@@ -2258,7 +2265,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		free(ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
 		ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1] =
 			xstrdup(hash_to_hex_algop(file_hash, ctx->r->hash_algo));
-		final_graph_name = get_split_graph_filename(ctx->odb_source,
+		final_graph_name = get_split_graph_filename(ctx->dir,
 					ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
 		free(ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1]);
 		ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1] = final_graph_name;
@@ -2310,7 +2317,7 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx,
 	    flags != COMMIT_GRAPH_SPLIT_REPLACE) {
 		while (g && (g->num_commits <= st_mult(size_mult, num_commits) ||
 			    (max_commits && num_commits > max_commits))) {
-			if (g->odb_source != ctx->odb_source)
+			if (strcmp(g->dir, ctx->dir))
 				break;
 
 			if (unsigned_add_overflows(num_commits, g->num_commits))
@@ -2332,10 +2339,10 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx,
 		    "should be 1 with --split=replace");
 
 	if (ctx->num_commit_graphs_after == 2) {
-		char *old_graph_name = get_commit_graph_filename(g->odb_source);
+		char *old_graph_name = get_commit_graph_filename(g->dir);
 
 		if (!strcmp(g->filename, old_graph_name) &&
-		    g->odb_source != ctx->odb_source) {
+		    strcmp(g->dir, ctx->dir)) {
 			ctx->num_commit_graphs_after = 1;
 			ctx->new_base_graph = NULL;
 		}
@@ -2505,13 +2512,13 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx)
 	if (ctx->opts && ctx->opts->expire_time)
 		expire_time = ctx->opts->expire_time;
 	if (!ctx->split) {
-		char *chain_file_name = get_commit_graph_chain_filename(ctx->odb_source);
+		char *chain_file_name = get_commit_graph_chain_filename(ctx->dir);
 		unlink(chain_file_name);
 		free(chain_file_name);
 		ctx->num_commit_graphs_after = 0;
 	}
 
-	strbuf_addstr(&path, ctx->odb_source->path);
+	strbuf_addstr(&path, ctx->dir);
 	strbuf_addstr(&path, "/info/commit-graphs");
 	dir = opendir(path.buf);
 
@@ -2553,16 +2560,15 @@ out:
 	strbuf_release(&path);
 }
 
-int write_commit_graph(struct odb_source *source,
+int write_commit_graph(struct repository *r,
+		       const char *dir,
 		       const struct string_list *const pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct commit_graph_opts *opts)
 {
-	struct repository *r = source->odb->repo;
 	struct write_commit_graph_context ctx = {
 		.r = r,
-		.odb_source = source,
 		.append = flags & COMMIT_GRAPH_WRITE_APPEND ? 1 : 0,
 		.report_progress = flags & COMMIT_GRAPH_WRITE_PROGRESS ? 1 : 0,
 		.split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0,
@@ -2593,6 +2599,8 @@ int write_commit_graph(struct odb_source *source,
 		return 0;
 	}
 
+	ctx.dir = absolute_pathdup(dir);
+
 	bloom_settings.hash_version = r->settings.commit_graph_changed_paths_version;
 	bloom_settings.bits_per_entry = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_BITS_PER_ENTRY",
 						      bloom_settings.bits_per_entry);
@@ -2715,6 +2723,7 @@ int write_commit_graph(struct odb_source *source,
 cleanup:
 	free(ctx.graph_name);
 	free(ctx.base_graph_name);
+	free(ctx.dir);
 	commit_stack_clear(&ctx.commits);
 	oid_array_clear(&ctx.oids);
 	clear_topo_level_slab(&topo_levels);
@@ -2767,7 +2776,7 @@ static int verify_one_commit_graph(struct commit_graph *g,
 				   struct progress *progress,
 				   uint64_t *seen)
 {
-	struct repository *r = g->odb_source->odb->repo;
+	struct repository *r = g->repo;
 	uint32_t i, cur_fanout_pos = 0;
 	struct object_id prev_oid, cur_oid;
 	struct commit *seen_gen_zero = NULL;
@@ -2931,7 +2940,7 @@ int verify_commit_graph(struct commit_graph *g, int flags)
 		if (!(flags & COMMIT_GRAPH_VERIFY_SHALLOW))
 			total += g->num_commits_in_base;
 
-		progress = start_progress(g->odb_source->odb->repo,
+		progress = start_progress(g->repo,
 					  _("Verifying commits in commit graph"),
 					  total);
 	}
@@ -2954,6 +2963,7 @@ void free_commit_graph(struct commit_graph *g)
 
 		if (g->data)
 			munmap((void *)g->data, g->data_len);
+		free(g->dir);
 		free(g->filename);
 		free(g->bloom_filter_settings);
 		free(g);

commit-graph.h

@@ -21,7 +21,7 @@
  * call this method outside of a builtin, and only if you know what
  * you are doing!
  */
-void git_test_write_commit_graph_or_die(struct odb_source *source);
+void git_test_write_commit_graph_or_die(struct repository *repo);
 
 struct commit;
 struct bloom_filter_settings;
@@ -29,8 +29,8 @@ struct repository;
 struct object_database;
 struct string_list;
 
-char *get_commit_graph_filename(struct odb_source *source);
-char *get_commit_graph_chain_filename(struct odb_source *source);
+char *get_commit_graph_filename(const char *dir);
+char *get_commit_graph_chain_filename(const char *dir);
 struct commit_graph *prepare_commit_graph(struct repository *r);
 int open_commit_graph(const char *graph_file, int *fd, struct stat *st);
 int open_commit_graph_chain(const char *chain_file, int *fd, struct stat *st,
@@ -86,12 +86,13 @@ struct commit_graph {
 	const unsigned char *data;
 	size_t data_len;
 
+	struct repository *repo;
 	const struct git_hash_algo *hash_algo;
 	unsigned char num_chunks;
 	uint32_t num_commits;
 	struct object_id oid;
+	char *dir;
 	char *filename;
-	struct odb_source *odb_source;
 
 	uint32_t num_commits_in_base;
 	unsigned int read_generation_data;
@@ -115,12 +116,20 @@ struct commit_graph {
 	struct bloom_filter_settings *bloom_filter_settings;
 };
 
-struct commit_graph *load_commit_graph_one_fd_st(struct odb_source *source,
+/*
+ * Load commit graphs from the given object directory `dir`. The directory may
+ * be given as a relative path; it is canonicalized internally so that graphs
+ * loaded from the same directory compare equal regardless of how the caller
+ * spelled the path.
+ */
+struct commit_graph *load_commit_graph_one_fd_st(struct repository *repo,
+						 const char *dir,
 						 int fd, struct stat *st);
 struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
 						   int fd, struct stat *st,
 						   int *incomplete_chain);
-struct commit_graph *read_commit_graph_one(struct odb_source *source);
+struct commit_graph *read_commit_graph_one(struct repository *repo,
+					   const char *dir);
 
 struct repo_settings;
 
@@ -172,11 +181,17 @@ struct commit_graph_opts {
  * and a negative value on failure. Note that if the repository
  * is not compatible with the commit-graph feature, then the
  * methods will return 0 without writing a commit-graph.
+ *
+ * The object directory `dir` may be given as a relative path; it is
+ * canonicalized internally so that it compares equal to the directory of
+ * graphs that have already been loaded.
  */
-int write_commit_graph_reachable(struct odb_source *source,
+int write_commit_graph_reachable(struct repository *repo,
+				 const char *dir,
 				 enum commit_graph_write_flags flags,
 				 const struct commit_graph_opts *opts);
-int write_commit_graph(struct odb_source *source,
+int write_commit_graph(struct repository *r,
+		       const char *dir,
 		       const struct string_list *pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,

diagnose.c

@@ -59,13 +59,13 @@ static void dir_file_stats_objects(const char *full_path,
 			    (uintmax_t)st.st_size);
 }
 
-static int dir_file_stats(struct odb_source *source, void *data)
+static int dir_file_stats(struct odb_files_dir *source, void *data)
 {
 	struct strbuf *buf = data;
 
-	strbuf_addf(buf, "Contents of %s:\n", source->path);
+	strbuf_addf(buf, "Contents of %s:\n", source->abspath);
 
-	for_each_file_in_pack_dir(source->path, dir_file_stats_objects,
+	for_each_file_in_pack_dir(source->abspath, dir_file_stats_objects,
 				  data);
 
 	return 0;
@@ -228,7 +228,7 @@ int create_diagnostics_archive(struct repository *r,
 
 	strbuf_reset(&buf);
 	strbuf_addstr(&buf, "--add-virtual-file=packs-local.txt:");
-	dir_file_stats(r->objects->sources, &buf);
+	dir_file_stats(odb_source_files_downcast(r->objects->source)->dirs, &buf);
 	odb_for_each_alternate(r->objects, dir_file_stats, &buf);
 	strvec_push(&archiver_args, buf.buf);
 

fetch-pack.c

@@ -1075,7 +1075,7 @@ static int get_pack(struct fetch_pack_args *args,
 		die(_("fetch-pack: unable to fork off %s"), cmd_name);
 	if (do_keep && (pack_lockfiles || fsck_objects)) {
 		int is_well_formed;
-		char *pack_lockfile = index_pack_lockfile(the_repository->objects->sources,
+		char *pack_lockfile = index_pack_lockfile(the_repository->objects->source,
 							  cmd.out,
 							  &is_well_formed);
 

http-walker.c

@@ -540,9 +540,9 @@ static int fetch_object(struct walker *walker, const struct object_id *oid)
 	} else if (!oideq(&obj_req->oid, &req->real_oid)) {
 		ret = error("File %s has bad hash", hex);
 	} else if (req->rename < 0) {
-		struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
+		struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 		struct strbuf buf = STRBUF_INIT;
-		odb_loose_path(files->loose, &buf, &req->oid);
+		odb_loose_path(files->dirs->loose, &buf, &req->oid);
 		ret = error("unable to write sha1 filename %s", buf.buf);
 		strbuf_release(&buf);
 	}

http.c

@@ -2757,9 +2757,9 @@ int finish_http_pack_request(struct http_pack_request *preq)
 void http_install_packfile(struct packed_git *p,
 			   struct packfile_list *list_to_remove_from)
 {
-	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 	packfile_list_remove(list_to_remove_from, p);
-	packfile_store_add_pack(files->packed, p);
+	packfile_store_add_pack(files->dirs->packed, p);
 }
 
 struct http_pack_request *new_http_pack_request(
@@ -2885,7 +2885,7 @@ static size_t fwrite_sha1_file(char *ptr, size_t eltsize, size_t nmemb,
 struct http_object_request *new_http_object_request(const char *base_url,
 						    const struct object_id *oid)
 {
-	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 	char *hex = oid_to_hex(oid);
 	struct strbuf filename = STRBUF_INIT;
 	struct strbuf prevfile = STRBUF_INIT;
@@ -2900,7 +2900,7 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	oidcpy(&freq->oid, oid);
 	freq->localfile = -1;
 
-	odb_loose_path(files->loose, &filename, oid);
+	odb_loose_path(files->dirs->loose, &filename, oid);
 	strbuf_addf(&freq->tmpfile, "%s.temp", filename.buf);
 
 	strbuf_addf(&prevfile, "%s.prev", filename.buf);
@@ -3026,7 +3026,7 @@ void process_http_object_request(struct http_object_request *freq)
 
 int finish_http_object_request(struct http_object_request *freq)
 {
-	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->source);
 	struct stat st;
 	struct strbuf filename = STRBUF_INIT;
 
@@ -3053,7 +3053,7 @@ int finish_http_object_request(struct http_object_request *freq)
 		unlink_or_warn(freq->tmpfile.buf);
 		return -1;
 	}
-	odb_loose_path(files->loose, &filename, &freq->oid);
+	odb_loose_path(files->dirs->loose, &filename, &freq->oid);
 	freq->rename = finalize_object_file(the_repository, freq->tmpfile.buf, filename.buf);
 	strbuf_release(&filename);
 

log-tree.c

@@ -1043,10 +1043,9 @@ static int do_remerge_diff(struct rev_info *opt,
 	 * into the alternative object store list as the primary.
 	 */
 	if (opt->remerge_diff && !opt->remerge_objdir) {
-		opt->remerge_objdir = tmp_objdir_create(the_repository, "remerge-diff");
+		opt->remerge_objdir = tmp_objdir_create(the_repository, "remerge-diff", 1);
 		if (!opt->remerge_objdir)
 			return error(_("unable to create temporary object directory"));
-		tmp_objdir_replace_primary_odb(opt->remerge_objdir, 1);
 	}
 
 	/* Setup merge options */

loose.c

@@ -113,11 +113,10 @@ err:
 
 int repo_read_loose_object_map(struct repository *repo)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
 
-	for (source = repo->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		if (loose_object_map_load(files->loose) < 0)
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (loose_object_map_load(dir->loose) < 0)
 			return -1;
 	}
 
@@ -126,8 +125,8 @@ int repo_read_loose_object_map(struct repository *repo)
 
 int repo_write_loose_object_map(struct repository *repo)
 {
-	struct odb_source_files *files = odb_source_files_downcast(repo->objects->sources);
-	kh_oid_map_t *map = files->loose->map->to_compat;
+	struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
+	kh_oid_map_t *map = files->dirs->loose->map->to_compat;
 	struct lock_file lock;
 	int fd;
 	khiter_t iter;
@@ -231,13 +230,12 @@ int repo_loose_object_map_oid(struct repository *repo,
 			      const struct git_hash_algo *to,
 			      struct object_id *dest)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
 	kh_oid_map_t *map;
 	khiter_t pos;
 
-	for (source = repo->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		struct loose_object_map *loose_map = files->loose->map;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		struct loose_object_map *loose_map = dir->loose->map;
 		if (!loose_map)
 			continue;
 		map = (to == repo->compat_hash_algo) ?

midx.c

@@ -835,28 +835,22 @@ void clear_incremental_midx_files_ext(struct odb_source_packed *source, const ch
 
 void clear_midx_file(struct repository *r)
 {
-	struct odb_source_files *files;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	struct strbuf midx = STRBUF_INIT;
 
-	if (r->objects) {
-		struct odb_source *source;
-
-		for (source = r->objects->sources; source; source = source->next) {
-			files = odb_source_files_downcast(source);
-			if (files->packed->midx)
-				close_midx(files->packed->midx);
-			files->packed->midx = NULL;
-		}
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (dir->packed->midx)
+			close_midx(dir->packed->midx);
+		dir->packed->midx = NULL;
 	}
 
-	files = odb_source_files_downcast(r->objects->sources);
-	get_midx_filename(files->packed, &midx);
+	get_midx_filename(files->dirs->packed, &midx);
 
 	if (remove_path(midx.buf))
 		die(_("failed to clear multi-pack-index at %s"), midx.buf);
 
-	clear_midx_files_ext(files->packed, MIDX_EXT_BITMAP, NULL);
-	clear_midx_files_ext(files->packed, MIDX_EXT_REV, NULL);
+	clear_midx_files_ext(files->dirs->packed, MIDX_EXT_BITMAP, NULL);
+	clear_midx_files_ext(files->dirs->packed, MIDX_EXT_REV, NULL);
 
 	strbuf_release(&midx);
 }
@@ -864,27 +858,24 @@ void clear_midx_file(struct repository *r)
 void clear_incremental_midx_files(struct repository *r,
 				  const struct strvec *keep_hashes)
 {
-	struct odb_source_files *files;
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	struct strbuf chain = STRBUF_INIT;
 
-	for (source = r->objects->sources; source; source = source->next) {
-		files = odb_source_files_downcast(source);
-		if (files->packed->midx)
-			close_midx(files->packed->midx);
-		files->packed->midx = NULL;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (dir->packed->midx)
+			close_midx(dir->packed->midx);
+		dir->packed->midx = NULL;
 	}
 
-	files = odb_source_files_downcast(r->objects->sources);
-	get_midx_chain_filename(files->packed, &chain);
+	get_midx_chain_filename(files->dirs->packed, &chain);
 
 	if (!keep_hashes && remove_path(chain.buf))
 		die(_("failed to clear multi-pack-index chain at %s"),
 		    chain.buf);
 
-	clear_incremental_midx_files_ext(files->packed, MIDX_EXT_BITMAP, keep_hashes);
-	clear_incremental_midx_files_ext(files->packed, MIDX_EXT_REV, keep_hashes);
-	clear_incremental_midx_files_ext(files->packed, MIDX_EXT_MIDX, keep_hashes);
+	clear_incremental_midx_files_ext(files->dirs->packed, MIDX_EXT_BITMAP, keep_hashes);
+	clear_incremental_midx_files_ext(files->dirs->packed, MIDX_EXT_REV, keep_hashes);
+	clear_incremental_midx_files_ext(files->dirs->packed, MIDX_EXT_MIDX, keep_hashes);
 
 	strbuf_release(&chain);
 }

object-file.c

@@ -488,7 +488,6 @@ struct odb_transaction_files {
 	enum odb_transaction_flags flags;
 
 	struct tmp_objdir *objdir;
-	struct odb_source *quarantine;
 	struct transaction_packfile packfile;
 	const char *prefix;
 
@@ -511,12 +510,10 @@ int odb_transaction_files_prepare(struct odb_transaction *base)
 	if (!transaction || transaction->objdir)
 		return 0;
 
-	transaction->objdir = tmp_objdir_create(base->source->odb->repo, transaction->prefix);
+	transaction->objdir = tmp_objdir_create(base->source->odb->repo, transaction->prefix, 0);
 	if (!transaction->objdir)
 		return error(_("unable to create temporary object directory"));
 
-	transaction->quarantine = tmp_objdir_replace_primary_odb(transaction->objdir, 0);
-
 	return 0;
 }
 
@@ -1447,8 +1444,7 @@ static int odb_transaction_files_write_pack(struct odb_transaction *base,
 			return -1;
 		}
 
-		odb_source_prepare(transaction->quarantine,
-				   ODB_PREPARE_FLUSH_CACHES);
+		odb_source_prepare(base->source, ODB_PREPARE_FLUSH_CACHES);
 	}
 
 	return 0;

odb.c

@@ -13,10 +13,10 @@
 #include "object-file.h"
 #include "object-name.h"
 #include "odb.h"
+#include "odb/source-files.h"
 #include "odb/source-inmemory.h"
 #include "path.h"
 #include "promisor-remote.h"
-#include "quote.h"
 #include "replace-object.h"
 #include "run-command.h"
 #include "setup.h"
@@ -27,48 +27,6 @@
 #include "trace2.h"
 #include "write-or-die.h"
 
-/*
- * NEEDSWORK: we're using "core.ignoreCase" to deduplicate alternates that
- * _may_ be the same. This requires quite a bit of boilerplate for dubious
- * benefit:
- *
- *   - Duplicating alternates should really only lead to regressed performance.
- *
- *   - We don't properly resolve symlinks or mointpoints, so we may still end
- *     up duplicating alternates.
- *
- *   - The value may be lying, in which case we might deduplicate alternates
- *     that are in fact not mapping to the same directory.
- *
- * We should investigate whether we can remove this whole mechanism outright.
- */
-static int odb_source_paths_cmp(struct object_database *o,
-				const char *a, const char *b)
-{
-	if (o->source_paths_icase < 0) {
-		int icase = 0;
-		repo_config_get_bool(o->repo, "core.ignorecase", &icase);
-		o->source_paths_icase = icase;
-	}
-
-	return o->source_paths_icase ? strcasecmp(a, b) : strcmp(a, b);
-}
-
-static int odb_source_by_path_cmp(const void *cb_data,
-				  const struct hashmap_entry *entry,
-				  const struct hashmap_entry *entry_or_key,
-				  const void *keydata)
-{
-	struct object_database *o = (struct object_database *)cb_data;
-	const struct odb_source *source = container_of(entry, const struct odb_source, by_path_entry);
-	const char *path = keydata;
-
-	if (!path)
-		path = container_of(entry_or_key, const struct odb_source, by_path_entry)->path;
-
-	return odb_source_paths_cmp(o, source->path, path);
-}
-
 int odb_mkstemp(struct object_database *odb,
 		struct strbuf *temp_filename, const char *pattern)
 {
@@ -90,199 +48,6 @@ int odb_mkstemp(struct object_database *odb,
 	return xmkstemp_mode(temp_filename->buf, mode);
 }
 
-/*
- * Return non-zero iff the path is usable as an alternate object database.
- */
-static bool odb_is_source_usable(struct object_database *o, const char *path)
-{
-	struct strbuf normalized_objdir = STRBUF_INIT;
-	struct hashmap_entry key;
-	bool usable = false;
-
-	strbuf_realpath(&normalized_objdir, o->sources->path, 1);
-
-	/* Detect cases where alternate disappeared */
-	if (!is_directory(path)) {
-		error(_("object directory %s does not exist; "
-			"check .git/objects/info/alternates"),
-		      path);
-		goto out;
-	}
-
-	/*
-	 * Prevent the common mistake of listing the same
-	 * thing twice, or object directory itself.
-	 */
-	if (!hashmap_get_size(&o->source_by_path)) {
-		assert(!o->sources->next);
-		hashmap_entry_init(&o->sources->by_path_entry,
-				   strihash(o->sources->path));
-		hashmap_add(&o->source_by_path, &o->sources->by_path_entry);
-	}
-
-	if (!odb_source_paths_cmp(o, path, normalized_objdir.buf))
-		goto out;
-
-	hashmap_entry_init(&key, strihash(path));
-	if (hashmap_get(&o->source_by_path, &key, path))
-		goto out;
-
-	usable = true;
-
-out:
-	strbuf_release(&normalized_objdir);
-	return usable;
-}
-
-void parse_alternates(const char *string,
-		      int sep,
-		      const char *relative_base,
-		      struct strvec *out)
-{
-	struct strbuf pathbuf = STRBUF_INIT;
-	struct strbuf buf = STRBUF_INIT;
-
-	if (!string || !*string)
-		return;
-
-	while (*string) {
-		const char *end;
-
-		strbuf_reset(&buf);
-		strbuf_reset(&pathbuf);
-
-		if (*string == '#') {
-			/* comment; consume up to next separator */
-			end = strchrnul(string, sep);
-		} else if (*string == '"' && !unquote_c_style(&buf, string, &end)) {
-			/*
-			 * quoted path; unquote_c_style has copied the
-			 * data for us and set "end". Broken quoting (e.g.,
-			 * an entry that doesn't end with a quote) falls
-			 * back to the unquoted case below.
-			 */
-		} else {
-			/* normal, unquoted path */
-			end = strchrnul(string, sep);
-			strbuf_add(&buf, string, end - string);
-		}
-
-		if (*end)
-			end++;
-		string = end;
-
-		if (!buf.len)
-			continue;
-
-		if (!is_absolute_path(buf.buf) && relative_base) {
-			strbuf_realpath(&pathbuf, relative_base, 1);
-			strbuf_addch(&pathbuf, '/');
-		}
-		strbuf_addbuf(&pathbuf, &buf);
-
-		strbuf_reset(&buf);
-		if (!strbuf_realpath(&buf, pathbuf.buf, 0)) {
-			error(_("unable to normalize alternate object path: %s"),
-			      pathbuf.buf);
-			continue;
-		}
-
-		/*
-		 * The trailing slash after the directory name is given by
-		 * this function at the end. Remove duplicates.
-		 */
-		while (buf.len && buf.buf[buf.len - 1] == '/')
-			strbuf_setlen(&buf, buf.len - 1);
-
-		strvec_push(out, buf.buf);
-	}
-
-	strbuf_release(&pathbuf);
-	strbuf_release(&buf);
-}
-
-static struct odb_source *odb_add_alternate_recursively(struct object_database *odb,
-							const char *source,
-							int depth)
-{
-	struct odb_source *alternate = NULL;
-	struct strvec sources = STRVEC_INIT;
-
-	if (!odb_is_source_usable(odb, source))
-		goto error;
-
-	alternate = odb_source_new(odb, source, false);
-
-	/* add the alternate entry */
-	*odb->sources_tail = alternate;
-	odb->sources_tail = &(alternate->next);
-
-	hashmap_entry_init(&alternate->by_path_entry, strihash(alternate->path));
-	if (hashmap_get(&odb->source_by_path, &alternate->by_path_entry,
-			alternate->path))
-		BUG("source must not yet exist");
-	hashmap_add(&odb->source_by_path, &alternate->by_path_entry);
-
-	/* recursively add alternates */
-	odb_source_read_alternates(alternate, &sources);
-	if (sources.nr && depth + 1 > 5) {
-		error(_("%s: ignoring alternate object stores, nesting too deep"),
-		      source);
-	} else {
-		for (size_t i = 0; i < sources.nr; i++)
-			odb_add_alternate_recursively(odb, sources.v[i], depth + 1);
-	}
-
- error:
-	strvec_clear(&sources);
-	return alternate;
-}
-
-struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
-						    const char *dir, int will_destroy,
-						    struct odb_source **prev_source)
-{
-	struct odb_source *source;
-
-	/*
-	 * Make a new primary odb and link the old primary ODB in as an
-	 * alternate
-	 */
-	source = odb_source_new(odb, dir, false);
-
-	/*
-	 * Disable ref updates while a temporary odb is active, since
-	 * the objects in the database may roll back.
-	 */
-	odb->repo->disable_ref_updates = true;
-	source->will_destroy = will_destroy;
-	source->next = odb->sources;
-	odb->sources = source;
-
-	if (prev_source)
-		*prev_source = source->next;
-
-	return source;
-}
-
-void odb_restore_primary_source(struct object_database *odb,
-				struct odb_source *restore_source,
-				const char *old_path)
-{
-	struct odb_source *cur_source = odb->sources;
-
-	if (strcmp(old_path, cur_source->path))
-		BUG("expected %s as primary object store; found %s",
-		    old_path, cur_source->path);
-
-	if (cur_source->next != restore_source)
-		BUG("we expect the old primary object store to be the first alternate");
-
-	odb->repo->disable_ref_updates = false;
-	odb->sources = restore_source;
-	odb_source_free(cur_source);
-}
-
 char *compute_alternate_path(const char *path, struct strbuf *err)
 {
 	char *ref_git = NULL;
@@ -347,32 +112,6 @@ out:
 	return ref_git;
 }
 
-struct odb_source *odb_find_source(struct object_database *odb, const char *obj_dir)
-{
-	struct odb_source *source;
-	char *obj_dir_real = real_pathdup(obj_dir, 1);
-	struct strbuf odb_path_real = STRBUF_INIT;
-
-	for (source = odb->sources; source; source = source->next) {
-		strbuf_realpath(&odb_path_real, source->path, 1);
-		if (!strcmp(obj_dir_real, odb_path_real.buf))
-			break;
-	}
-
-	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;
-}
-
 static void fill_alternate_refs_command(struct repository *repo,
 					struct child_process *cmd,
 					const char *repo_path)
@@ -435,18 +174,19 @@ static void read_alternate_refs(struct repository *repo,
 }
 
 struct alternate_refs_data {
+	struct repository *repo;
 	odb_for_each_alternate_ref_fn *fn;
 	void *payload;
 };
 
-static int refs_from_alternate_cb(struct odb_source *alternate,
+static int refs_from_alternate_cb(struct odb_files_dir *alternate,
 				  void *payload)
 {
 	struct strbuf path = STRBUF_INIT;
 	size_t base_len;
 	struct alternate_refs_data *cb = payload;
 
-	if (!strbuf_realpath(&path, alternate->path, 0))
+	if (!strbuf_realpath(&path, alternate->abspath, 0))
 		goto out;
 	if (!strbuf_strip_suffix(&path, "/objects"))
 		goto out;
@@ -458,7 +198,7 @@ static int refs_from_alternate_cb(struct odb_source *alternate,
 		goto out;
 	strbuf_setlen(&path, base_len);
 
-	read_alternate_refs(alternate->odb->repo, path.buf, cb->fn, cb->payload);
+	read_alternate_refs(cb->repo, path.buf, cb->fn, cb->payload);
 
 out:
 	strbuf_release(&path);
@@ -468,43 +208,33 @@ out:
 void odb_for_each_alternate_ref(struct object_database *odb,
 				odb_for_each_alternate_ref_fn cb, void *payload)
 {
-	struct alternate_refs_data data;
-	data.fn = cb;
-	data.payload = payload;
+	struct alternate_refs_data data = {
+		.fn = cb,
+		.payload = payload,
+		.repo = odb->repo,
+	};
 	odb_for_each_alternate(odb, refs_from_alternate_cb, &data);
 }
 
 int odb_for_each_alternate(struct object_database *odb,
 			 odb_for_each_alternate_fn cb, void *payload)
 {
-	struct odb_source *alternate;
+	struct odb_source_files *files = odb_source_files_downcast(odb->source);
 	int r = 0;
 
-	for (alternate = odb->sources->next; alternate; alternate = alternate->next) {
-		r = cb(alternate, payload);
+	for (struct odb_files_dir *dir = files->dirs->next; dir; dir = dir->next) {
+		r = cb(dir, payload);
 		if (r)
 			break;
 	}
 	return r;
 }
 
-static void odb_prepare_alternates(struct object_database *odb,
-				   const char *alternate_db)
-{
-	struct strvec sources = STRVEC_INIT;
-
-	parse_alternates(alternate_db, PATH_SEP, NULL, &sources);
-	odb_source_read_alternates(odb->sources, &sources);
-
-	for (size_t i = 0; i < sources.nr; i++)
-		odb_add_alternate_recursively(odb, sources.v[i], 0);
-
-	strvec_clear(&sources);
-}
-
 int odb_has_alternates(struct object_database *odb)
 {
-	return !!odb->sources->next;
+	if (odb->source->type != ODB_SOURCE_FILES)
+		return 0;
+	return !!odb_source_files_downcast(odb->source)->dirs->next;
 }
 
 int obj_read_use_lock = 0;
@@ -548,16 +278,12 @@ static enum odb_read_status do_oid_object_info_extended(struct object_database *
 		return 0;
 
 	while (1) {
-		struct odb_source *source;
-
-		for (source = odb->sources; source; source = source->next) {
-			ret = odb_source_read_object_info(source, real, oi, flags,
-							  corrupt_err.len ? NULL : &corrupt_err);
-			if (!ret)
-				goto out;
-			if (ret != ODB_READ_NOT_FOUND)
-				corrupt = true;
-		}
+		ret = odb_source_read_object_info(odb->source, real, oi, flags,
+						  corrupt_err.len ? NULL : &corrupt_err);
+		if (!ret)
+			goto out;
+		if (ret != ODB_READ_NOT_FOUND)
+			corrupt = true;
 
 		/*
 		 * When the object hasn't been found we try a second read and
@@ -565,15 +291,13 @@ static enum odb_read_status do_oid_object_info_extended(struct object_database *
 		 * caches or reload on-disk state.
 		 */
 		if (!(flags & OBJECT_INFO_QUICK)) {
-			for (source = odb->sources; source; source = source->next) {
-				ret = odb_source_read_object_info(source, real, oi,
-								  flags | OBJECT_INFO_SECOND_READ,
-								  corrupt_err.len ? NULL : &corrupt_err);
-				if (!ret)
-					goto out;
-				if (ret != ODB_READ_NOT_FOUND)
-					corrupt = true;
-			}
+			ret = odb_source_read_object_info(odb->source, real, oi,
+							  flags | OBJECT_INFO_SECOND_READ,
+							  corrupt_err.len ? NULL : &corrupt_err);
+			if (!ret)
+				goto out;
+			if (ret != ODB_READ_NOT_FOUND)
+				corrupt = true;
 		}
 
 		/* Check if it is a missing object */
@@ -815,11 +539,7 @@ int odb_has_object(struct object_database *odb, const struct object_id *oid,
 int odb_freshen_object(struct object_database *odb,
 		       const struct object_id *oid)
 {
-	struct odb_source *source;
-	for (source = odb->sources; source; source = source->next)
-		if (odb_source_freshen_object(source, oid, NULL))
-			return 1;
-	return 0;
+	return odb_source_freshen_object(odb->source, oid, NULL);
 }
 
 int odb_for_each_object_ext(struct object_database *odb,
@@ -828,18 +548,7 @@ int odb_for_each_object_ext(struct object_database *odb,
 			    void *cb_data,
 			    const struct odb_for_each_object_options *opts)
 {
-	int ret;
-
-	for (struct odb_source *source = odb->sources; source; source = source->next) {
-		if (opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY && !source->local)
-			continue;
-
-		ret = odb_source_for_each_object(source, request, cb, cb_data, opts);
-		if (ret)
-			return ret;
-	}
-
-	return 0;
+	return odb_source_for_each_object(odb->source, request, cb, cb_data, opts);
 }
 
 int odb_for_each_object(struct object_database *odb,
@@ -858,7 +567,6 @@ int odb_count_objects(struct object_database *odb,
 		      enum odb_count_objects_flags flags,
 		      unsigned long *out)
 {
-	struct odb_source *source;
 	unsigned long count = 0;
 	int ret;
 
@@ -867,15 +575,9 @@ int odb_count_objects(struct object_database *odb,
 		return 0;
 	}
 
-	for (source = odb->sources; source; source = source->next) {
-		unsigned long c;
-
-		ret = odb_source_count_objects(source, flags, &c);
-		if (ret < 0)
-			goto out;
-
-		count += c;
-	}
+	ret = odb_source_count_objects(odb->source, flags, &count);
+	if (ret < 0)
+		goto out;
 
 	odb->object_count = count;
 	odb->object_count_valid = 1;
@@ -946,13 +648,7 @@ int odb_find_abbrev_len(struct object_database *odb,
 		goto out;
 	}
 
-	for (struct odb_source *source = odb->sources; source; source = source->next) {
-		ret = odb_source_find_abbrev_len(source, oid, len, &len);
-		if (ret)
-			goto out;
-	}
-
-	ret = 0;
+	ret = odb_source_find_abbrev_len(odb->source, oid, len, &len);
 	*out = len;
 
 out:
@@ -1008,7 +704,7 @@ int odb_write_object_ext(struct object_database *odb,
 		compat_oid_p = &compat_oid;
 	}
 
-	return odb_source_write_object(odb->sources, buf, len, type,
+	return odb_source_write_object(odb->source, buf, len, type,
 				       oid, compat_oid_p, NULL, flags);
 }
 
@@ -1016,19 +712,19 @@ int odb_write_object_stream(struct object_database *odb,
 			    struct odb_stream *stream,
 			    struct object_id *oid)
 {
-	return odb_source_write_object_stream(odb->sources, stream, oid);
+	return odb_source_write_object_stream(odb->source, stream, oid);
 }
 
 int odb_optimize(struct object_database *odb,
 		 const struct odb_optimize_options *opts)
 {
-	return odb_source_optimize(odb->sources, opts);
+	return odb_source_optimize(odb->source, opts);
 }
 
 bool odb_optimize_required(struct object_database *odb,
 			   const struct odb_optimize_options *opts)
 {
-	return odb_source_optimize_required(odb->sources, opts);
+	return odb_source_optimize_required(odb->source, opts);
 }
 
 void odb_generate_pack_options_release(struct odb_generate_pack_options *opts)
@@ -1042,9 +738,9 @@ int odb_generate_pack(struct object_database *odb,
 		      struct odb_pack_generator **out,
 		      const struct odb_generate_pack_options *opts)
 {
-	if (!odb->sources->generate_pack)
+	if (!odb->source->generate_pack)
 		return error(_("primary object source does not support generating packfiles"));
-	return odb_source_generate_pack(odb->sources, out, opts);
+	return odb_source_generate_pack(odb->source, out, opts);
 }
 
 int odb_pack_generator_finish(struct odb_pack_generator *generator)
@@ -1055,55 +751,29 @@ int odb_pack_generator_finish(struct odb_pack_generator *generator)
 struct object_database *odb_new(struct repository *repo,
 				enum odb_new_flags flags)
 {
-	char *primary_source = NULL, *secondary_sources = NULL;
 	struct object_database *o;
 
 	CALLOC_ARRAY(o, 1);
 	o->repo = repo;
 	pthread_mutex_init(&o->replace_mutex, NULL);
-	hashmap_init(&o->source_by_path, odb_source_by_path_cmp, o, 0);
-	o->source_paths_icase = -1;
 
-	if (flags & ODB_NEW_HONOR_ENV) {
-		primary_source = xstrdup_or_null(getenv(DB_ENVIRONMENT));
-		secondary_sources = xstrdup_or_null(getenv(ALTERNATE_DB_ENVIRONMENT));
-	}
-	if (!primary_source)
-		primary_source = xstrfmt("%s/objects", repo->commondir);
-
-	o->sources = odb_source_new(o, primary_source, true);
-	o->sources_tail = &o->sources->next;
+	o->source = odb_source_new(o, flags);
 	o->inmemory_objects = &odb_source_inmemory_new(o)->base;
 
-	odb_prepare_alternates(o, secondary_sources);
-
-	free(secondary_sources);
-	free(primary_source);
 	return o;
 }
 
 void odb_close(struct object_database *o)
 {
-	struct odb_source *source;
-	for (source = o->sources; source; source = source->next)
-		odb_source_close(source);
+	odb_source_close(o->source);
 	close_commit_graph(o);
 }
 
 static void odb_free_sources(struct object_database *o)
 {
-	while (o->sources) {
-		struct odb_source *next;
-
-		next = o->sources->next;
-		odb_source_free(o->sources);
-		o->sources = next;
-	}
-
+	odb_source_free(o->source);
 	odb_source_free(o->inmemory_objects);
 	o->inmemory_objects = NULL;
-
-	hashmap_clear(&o->source_by_path);
 }
 
 void odb_free(struct object_database *o)
@@ -1122,24 +792,12 @@ void odb_free(struct object_database *o)
 
 void odb_prepare(struct object_database *o, enum odb_prepare_flags flags)
 {
-	struct odb_source *source;
-
 	obj_read_lock();
 
-	/*
-	 * Reprepare alt odbs, in case the alternates file was modified
-	 * during the course of this process. This only _adds_ odbs to
-	 * the linked list, so existing odbs will continue to exist for
-	 * the lifetime of the process. Consequently, we don't have to
-	 * reprocess GIT_ALTERNATE_OBJECT_DIRECTORIES here.
-	 */
-	if (flags & ODB_PREPARE_FLUSH_CACHES) {
-		odb_prepare_alternates(o, NULL);
+	if (flags & ODB_PREPARE_FLUSH_CACHES)
 		o->object_count_valid = 0;
-	}
 
-	for (source = o->sources; source; source = source->next)
-		odb_source_prepare(source, flags);
+	odb_source_prepare(o->source, flags);
 
 	obj_read_unlock();
 }
@@ -1151,8 +809,5 @@ void odb_reprepare(struct object_database *o)
 
 int odb_fsck(struct object_database *odb, struct odb_fsck_options *options)
 {
-	int ret = 0;
-	for (struct odb_source *source = odb->sources; source; source = source->next)
-		ret |= odb_source_fsck(source, options);
-	return ret;
+	return odb_source_fsck(odb->source, options);
 }

odb.h

@@ -12,6 +12,7 @@
 struct cached_object_entry;
 struct list_objects_filter_options;
 struct odb_source_inmemory;
+struct odb_files_dir;
 struct packed_git;
 struct repository;
 struct strbuf;
@@ -27,13 +28,16 @@ char *compute_alternate_path(const char *path, struct strbuf *err);
 
 /*
  * The object database encapsulates access to objects in a repository. It
- * manages one or more sources that store the actual objects which are
- * configured via alternates.
+ * manages the object source as well as auxiliary data structures required to
+ * manage objects.
  */
 struct object_database {
 	/* Repository that owns this database. */
 	struct repository *repo;
 
+	/* The source backing this object database. */
+	struct odb_source *source;
+
 	/*
 	 * State of current object database transaction. Only one
 	 * transaction may be pending at a time. Is NULL when no transaction is
@@ -41,27 +45,6 @@ struct object_database {
 	 */
 	struct odb_transaction *transaction;
 
-	/*
-	 * Set of all object directories; the main directory is first (and
-	 * cannot be NULL after initialization). Subsequent directories are
-	 * alternates.
-	 */
-	struct odb_source *sources;
-	struct odb_source **sources_tail;
-
-	/*
-	 * Map of object database sources, keyed by their respective paths.
-	 * This map is used to detect the case where the same source is
-	 * registered multiple times.
-	 */
-	struct hashmap source_by_path;
-
-	/*
-	 * Whether source paths shall be compared case-insensitively, as
-	 * determined by "core.ignoreCase".
-	 */
-	int source_paths_icase;
-
 	/*
 	 * Objects that should be substituted by other objects
 	 * (see git-replace(1)).
@@ -225,39 +208,13 @@ struct odb_fsck_options {
  */
 int odb_fsck(struct object_database *odb, struct odb_fsck_options *opts);
 
-/*
- * 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 and return the newly installed primary source. The former
- * primary source is reported via `prev_source` when non-NULL.
- */
-struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
-						    const char *dir, int will_destroy,
-						    struct odb_source **prev_source);
-
-/*
- * Restore the primary source that was previously replaced by
- * `odb_set_temporary_primary_source()`.
- */
-void odb_restore_primary_source(struct object_database *odb,
-				struct odb_source *restore_source,
-				const char *old_path);
-
 /*
  * Iterate through all alternates of the database and execute the provided
  * callback function for each of them. Stop iterating once the callback
  * function returns a non-zero value, in which case the value is bubbled up
  * from the callback.
  */
-typedef int odb_for_each_alternate_fn(struct odb_source *, void *);
+typedef int odb_for_each_alternate_fn(struct odb_files_dir *, void *);
 int odb_for_each_alternate(struct object_database *odb,
 			   odb_for_each_alternate_fn cb, void *payload);
 
@@ -847,9 +804,4 @@ int odb_generate_pack(struct object_database *odb,
  */
 int odb_pack_generator_finish(struct odb_pack_generator *generator);
 
-void parse_alternates(const char *string,
-		      int sep,
-		      const char *relative_base,
-		      struct strvec *out);
-
 #endif /* ODB_H */

odb/source-files.c

@@ -15,6 +15,7 @@
 #include "packfile.h"
 #include "path.h"
 #include "promisor-remote.h"
+#include "quote.h"
 #include "repack.h"
 #include "run-command.h"
 #include "strbuf.h"
@@ -24,6 +25,30 @@
 #include "tree.h"
 #include "write-or-die.h"
 
+struct odb_files_dir *odb_files_dir_new(struct object_database *odb,
+					const char *path, bool local)
+{
+	struct odb_files_dir *dir;
+
+	CALLOC_ARRAY(dir, 1);
+	dir->abspath = absolute_pathdup(path);
+	dir->local = local;
+	dir->loose = odb_source_loose_new(odb, path, local);
+	dir->packed = odb_source_packed_new(odb, path, local);
+
+	return dir;
+}
+
+void odb_files_dir_free(struct odb_files_dir *dir)
+{
+	if (!dir)
+		return;
+	odb_source_free(&dir->loose->base);
+	odb_source_free(&dir->packed->base);
+	free(dir->abspath);
+	free(dir);
+}
+
 static void odb_source_files_reparent(const char *old_cwd,
 				      const char *new_cwd,
 				      void *cb_data)
@@ -31,6 +56,7 @@ static void odb_source_files_reparent(const char *old_cwd,
 	struct odb_source_files *files = cb_data;
 	char *path = reparent_relative_path(old_cwd, new_cwd,
 					    files->base.path);
+
 	free(files->base.path);
 	files->base.path = path;
 }
@@ -38,9 +64,16 @@ static void odb_source_files_reparent(const char *old_cwd,
 static void odb_source_files_free(struct odb_source *source)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
+
 	chdir_notify_unregister(odb_source_files_reparent, files);
-	odb_source_free(&files->loose->base);
-	odb_source_free(&files->packed->base);
+
+	while (files->dirs) {
+		struct odb_files_dir *next = files->dirs->next;
+		odb_files_dir_free(files->dirs);
+		files->dirs = next;
+	}
+	hashmap_clear(&files->dirs_by_path);
+
 	odb_source_release(&files->base);
 	free(files);
 }
@@ -48,8 +81,11 @@ static void odb_source_files_free(struct odb_source *source)
 static void odb_source_files_close(struct odb_source *source)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	odb_source_close(&files->loose->base);
-	odb_source_close(&files->packed->base);
+
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		odb_source_close(&dir->loose->base);
+		odb_source_close(&dir->packed->base);
+	}
 }
 
 static int odb_source_files_create_on_disk(struct odb_source *source,
@@ -140,12 +176,246 @@ out:
 	return ret;
 }
 
+/*
+ * NEEDSWORK: we're using "core.ignoreCase" to deduplicate alternates that
+ * _may_ be the same. This requires quite a bit of boilerplate for dubious
+ * benefit:
+ *
+ *   - Duplicating alternates should really only lead to regressed performance.
+ *
+ *   - We don't properly resolve symlinks or mointpoints, so we may still end
+ *     up duplicating alternates.
+ *
+ *   - The value may be lying, in which case we might deduplicate alternates
+ *     that are in fact not mapping to the same directory.
+ *
+ * We should investigate whether we can remove this whole mechanism outright.
+ */
+static int odb_files_dir_paths_cmp(struct odb_source_files *files,
+				   const char *a, const char *b)
+{
+	if (files->dirs_paths_icase < 0) {
+		int icase = 0;
+		repo_config_get_bool(files->base.odb->repo, "core.ignorecase", &icase);
+		files->dirs_paths_icase = icase;
+	}
+
+	return files->dirs_paths_icase ? strcasecmp(a, b) : strcmp(a, b);
+}
+
+static int odb_files_dir_by_path_cmp(const void *cb_data,
+				     const struct hashmap_entry *entry,
+				     const struct hashmap_entry *entry_or_key,
+				     const void *keydata)
+{
+	struct odb_source_files *files = (struct odb_source_files *)cb_data;
+	const struct odb_files_dir *dir = container_of(entry, const struct odb_files_dir, by_path_entry);
+	const char *path = keydata;
+
+	if (!path)
+		path = container_of(entry_or_key, const struct odb_files_dir, by_path_entry)->abspath;
+
+	return odb_files_dir_paths_cmp(files, dir->abspath, path);
+}
+
+/*
+ * Return non-zero iff the path is usable as an alternate object directory.
+ */
+static bool odb_files_dir_is_usable(struct odb_source_files *files,
+				    const char *path)
+{
+	struct strbuf normalized_objdir = STRBUF_INIT;
+	struct hashmap_entry key;
+	bool usable = false;
+
+	strbuf_realpath(&normalized_objdir, files->dirs->abspath, 1);
+
+	/* Detect cases where alternate disappeared */
+	if (!is_directory(path)) {
+		error(_("object directory %s does not exist; "
+			"check .git/objects/info/alternates"),
+		      path);
+		goto out;
+	}
+
+	/*
+	 * Prevent the common mistake of listing the same
+	 * thing twice, or object directory itself.
+	 */
+	if (!hashmap_get_size(&files->dirs_by_path)) {
+		assert(!files->dirs->next);
+		hashmap_entry_init(&files->dirs->by_path_entry,
+				   strihash(files->dirs->abspath));
+		hashmap_add(&files->dirs_by_path, &files->dirs->by_path_entry);
+	}
+
+	if (!odb_files_dir_paths_cmp(files, path, normalized_objdir.buf))
+		goto out;
+
+	hashmap_entry_init(&key, strihash(path));
+	if (hashmap_get(&files->dirs_by_path, &key, path))
+		goto out;
+
+	usable = true;
+
+out:
+	strbuf_release(&normalized_objdir);
+	return usable;
+}
+
+static void parse_alternates(const char *string,
+			     int sep,
+			     const char *relative_base,
+			     struct strvec *out)
+{
+	struct strbuf pathbuf = STRBUF_INIT;
+	struct strbuf buf = STRBUF_INIT;
+
+	if (!string || !*string)
+		return;
+
+	while (*string) {
+		const char *end;
+
+		strbuf_reset(&buf);
+		strbuf_reset(&pathbuf);
+
+		if (*string == '#') {
+			/* comment; consume up to next separator */
+			end = strchrnul(string, sep);
+		} else if (*string == '"' && !unquote_c_style(&buf, string, &end)) {
+			/*
+			 * quoted path; unquote_c_style has copied the
+			 * data for us and set "end". Broken quoting (e.g.,
+			 * an entry that doesn't end with a quote) falls
+			 * back to the unquoted case below.
+			 */
+		} else {
+			/* normal, unquoted path */
+			end = strchrnul(string, sep);
+			strbuf_add(&buf, string, end - string);
+		}
+
+		if (*end)
+			end++;
+		string = end;
+
+		if (!buf.len)
+			continue;
+
+		if (!is_absolute_path(buf.buf) && relative_base) {
+			strbuf_realpath(&pathbuf, relative_base, 1);
+			strbuf_addch(&pathbuf, '/');
+		}
+		strbuf_addbuf(&pathbuf, &buf);
+
+		strbuf_reset(&buf);
+		if (!strbuf_realpath(&buf, pathbuf.buf, 0)) {
+			error(_("unable to normalize alternate object path: %s"),
+			      pathbuf.buf);
+			continue;
+		}
+
+		/*
+		 * The trailing slash after the directory name is given by
+		 * this function at the end. Remove duplicates.
+		 */
+		while (buf.len && buf.buf[buf.len - 1] == '/')
+			strbuf_setlen(&buf, buf.len - 1);
+
+		strvec_push(out, buf.buf);
+	}
+
+	strbuf_release(&pathbuf);
+	strbuf_release(&buf);
+}
+
+static int read_alternates(const char *object_dir, struct strvec *out)
+{
+	struct strbuf buf = STRBUF_INIT;
+	char *path;
+
+	path = xstrfmt("%s/info/alternates", object_dir);
+	if (strbuf_read_file(&buf, path, 1024) < 0) {
+		warn_on_fopen_errors(path);
+		free(path);
+		return 0;
+	}
+	parse_alternates(buf.buf, '\n', object_dir, out);
+
+	strbuf_release(&buf);
+	free(path);
+	return 0;
+}
+
+static void odb_add_alternate_recursively(struct odb_source_files *files,
+					  const char *path,
+					  int depth)
+{
+	struct odb_files_dir *alternate;
+	struct strvec alternates = STRVEC_INIT;
+
+	if (!odb_files_dir_is_usable(files, path))
+		goto out;
+
+	alternate = odb_files_dir_new(files->base.odb, path, false);
+
+	/* add the alternate entry */
+	*files->dirs_tail = alternate;
+	files->dirs_tail = &(alternate->next);
+
+	hashmap_entry_init(&alternate->by_path_entry, strihash(alternate->abspath));
+	if (hashmap_get(&files->dirs_by_path, &alternate->by_path_entry,
+			alternate->abspath))
+		BUG("object directory must not yet exist");
+	hashmap_add(&files->dirs_by_path, &alternate->by_path_entry);
+
+	/* recursively add alternates */
+	read_alternates(alternate->abspath, &alternates);
+	if (alternates.nr && depth + 1 > 5) {
+		error(_("%s: ignoring alternate object stores, nesting too deep"),
+		      path);
+	} else {
+		for (size_t i = 0; i < alternates.nr; i++)
+			odb_add_alternate_recursively(files, alternates.v[i], depth + 1);
+	}
+
+ out:
+	strvec_clear(&alternates);
+}
+
+static void odb_prepare_alternates(struct odb_source_files *files,
+				   const char *alternate_db)
+{
+	struct strvec alternates = STRVEC_INIT;
+
+	parse_alternates(alternate_db, PATH_SEP, NULL, &alternates);
+	read_alternates(files->dirs->abspath, &alternates);
+
+	for (size_t i = 0; i < alternates.nr; i++)
+		odb_add_alternate_recursively(files, alternates.v[i], 0);
+
+	strvec_clear(&alternates);
+}
+
 static void odb_source_files_prepare(struct odb_source *source,
 				     enum odb_prepare_flags flags)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	odb_source_prepare(&files->loose->base, flags);
-	odb_source_prepare(&files->packed->base, flags);
+
+	/*
+	 * Reprepare alternates, in case the alternates file was modified
+	 * during the course of this process. This only _adds_ directories to
+	 * the linked list, so existing directories will continue to exist
+	 * for the lifetime of the process.
+	 */
+	if (flags & ODB_PREPARE_FLUSH_CACHES)
+		odb_prepare_alternates(files, NULL);
+
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		odb_source_prepare(&dir->loose->base, flags);
+		odb_source_prepare(&dir->packed->base, flags);
+	}
 }
 
 static enum odb_read_status odb_source_files_read_object_info(struct odb_source *source,
@@ -155,28 +425,33 @@ static enum odb_read_status odb_source_files_read_object_info(struct odb_source
 							      struct strbuf *errmsg)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	enum odb_read_status ret_packed, ret_loose;
-
-	ret_packed = odb_source_read_object_info(&files->packed->base, oid, oi,
-						 flags, errmsg);
-	if (!ret_packed)
-		return 0;
-
-	ret_loose = odb_source_read_object_info(&files->loose->base, oid, oi, flags,
-						ret_packed == ODB_READ_NOT_FOUND ? errmsg : NULL);
-	if (!ret_loose)
-		return 0;
+	enum odb_read_status status = ODB_READ_NOT_FOUND;
 
 	/*
-	 * Reading the packed object may have failed even though the object
-	 * exists, for example because it is corrupt. Report this failure to
-	 * the caller in case neither of the sources was able to read the
-	 * object, and prefer the error of the packed source in case both
-	 * reads have failed.
+	 * Reading an object may fail even though the object exists, for
+	 * example because it is corrupt. Report this failure to the caller in
+	 * case none of the directories was able to read the object, and
+	 * prefer the first such error in case multiple reads have failed.
 	 */
-	if (ret_packed != ODB_READ_NOT_FOUND)
-		return ret_packed;
-	return ret_loose;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		enum odb_read_status ret;
+
+		ret = odb_source_read_object_info(&dir->packed->base, oid, oi, flags,
+						  status == ODB_READ_NOT_FOUND ? errmsg : NULL);
+		if (!ret)
+			return 0;
+		if (ret != ODB_READ_NOT_FOUND && status == ODB_READ_NOT_FOUND)
+			status = ret;
+
+		ret = odb_source_read_object_info(&dir->loose->base, oid, oi, flags,
+						  status == ODB_READ_NOT_FOUND ? errmsg : NULL);
+		if (!ret)
+			return 0;
+		if (ret != ODB_READ_NOT_FOUND && status == ODB_READ_NOT_FOUND)
+			status = ret;
+	}
+
+	return status;
 }
 
 static int odb_source_files_read_object_stream(struct odb_stream **out,
@@ -184,9 +459,12 @@ static int odb_source_files_read_object_stream(struct odb_stream **out,
 					       const struct object_id *oid)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	if (!odb_source_read_object_stream(out, &files->packed->base, oid) ||
-	    !odb_source_read_object_stream(out, &files->loose->base, oid))
-		return 0;
+
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next)
+		if (!odb_source_read_object_stream(out, &dir->packed->base, oid) ||
+		    !odb_source_read_object_stream(out, &dir->loose->base, oid))
+			return 0;
+
 	return -1;
 }
 
@@ -199,16 +477,21 @@ static int odb_source_files_for_each_object(struct odb_source *source,
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	int ret;
 
-	if (!(opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY)) {
-		ret = odb_source_for_each_object(&files->loose->base, request, cb, cb_data, opts);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY && !dir->local)
+			continue;
+
+		if (!(opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY)) {
+			ret = odb_source_for_each_object(&dir->loose->base, request, cb, cb_data, opts);
+			if (ret)
+				return ret;
+		}
+
+		ret = odb_source_for_each_object(&dir->packed->base, request, cb, cb_data, opts);
 		if (ret)
 			return ret;
 	}
 
-	ret = odb_source_for_each_object(&files->packed->base, request, cb, cb_data, opts);
-	if (ret)
-		return ret;
-
 	return 0;
 }
 
@@ -217,21 +500,23 @@ static int odb_source_files_count_objects(struct odb_source *source,
 					  unsigned long *out)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	unsigned long count;
+	unsigned long count = 0;
 	int ret;
 
-	ret = odb_source_count_objects(&files->packed->base, flags, &count);
-	if (ret < 0)
-		goto out;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		unsigned long dir_count;
 
-	if (!(flags & ODB_COUNT_OBJECTS_APPROXIMATE)) {
-		unsigned long loose_count;
-
-		ret = odb_source_count_objects(&files->loose->base, flags, &loose_count);
+		ret = odb_source_count_objects(&dir->packed->base, flags, &dir_count);
 		if (ret < 0)
 			goto out;
+		count += dir_count;
 
-		count += loose_count;
+		if (!(flags & ODB_COUNT_OBJECTS_APPROXIMATE)) {
+			ret = odb_source_count_objects(&dir->loose->base, flags, &dir_count);
+			if (ret < 0)
+				goto out;
+			count += dir_count;
+		}
 	}
 
 	*out = count;
@@ -248,15 +533,17 @@ static int odb_source_files_find_abbrev_len(struct odb_source *source,
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	unsigned len = min_len;
-	int ret;
+	int ret = 0;
 
-	ret = odb_source_find_abbrev_len(&files->packed->base, oid, len, &len);
-	if (ret < 0)
-		goto out;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		ret = odb_source_find_abbrev_len(&dir->packed->base, oid, len, &len);
+		if (ret < 0)
+			goto out;
 
-	ret = odb_source_find_abbrev_len(&files->loose->base, oid, len, &len);
-	if (ret < 0)
-		goto out;
+		ret = odb_source_find_abbrev_len(&dir->loose->base, oid, len, &len);
+		if (ret < 0)
+			goto out;
+	}
 
 	*out = len;
 	ret = 0;
@@ -270,9 +557,12 @@ static int odb_source_files_freshen_object(struct odb_source *source,
 					   const time_t *mtime)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	if (odb_source_freshen_object(&files->packed->base, oid, mtime) ||
-	    odb_source_freshen_object(&files->loose->base, oid, mtime))
-		return 1;
+
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next)
+		if (odb_source_freshen_object(&dir->packed->base, oid, mtime) ||
+		    odb_source_freshen_object(&dir->loose->base, oid, mtime))
+			return 1;
+
 	return 0;
 }
 
@@ -285,7 +575,7 @@ static int odb_source_files_write_object(struct odb_source *source,
 					 enum odb_write_object_flags flags)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	return odb_source_write_object(&files->loose->base, buf, len, type,
+	return odb_source_write_object(&files->dirs->loose->base, buf, len, type,
 				       oid, compat_oid, mtime, flags);
 }
 
@@ -294,7 +584,7 @@ static int odb_source_files_write_object_stream(struct odb_source *source,
 						struct object_id *oid)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	return odb_source_write_object_stream(&files->loose->base, stream, oid);
+	return odb_source_write_object_stream(&files->dirs->loose->base, stream, oid);
 }
 
 static int odb_source_files_begin_transaction(struct odb_source *source,
@@ -304,25 +594,6 @@ static int odb_source_files_begin_transaction(struct odb_source *source,
 	return odb_transaction_files_begin(source, out, flags);
 }
 
-static int odb_source_files_read_alternates(struct odb_source *source,
-					    struct strvec *out)
-{
-	struct strbuf buf = STRBUF_INIT;
-	char *path;
-
-	path = xstrfmt("%s/info/alternates", source->path);
-	if (strbuf_read_file(&buf, path, 1024) < 0) {
-		warn_on_fopen_errors(path);
-		free(path);
-		return 0;
-	}
-	parse_alternates(buf.buf, '\n', source->path, out);
-
-	strbuf_release(&buf);
-	free(path);
-	return 0;
-}
-
 static int too_many_loose_objects(struct odb_source_files *files, int limit)
 {
 	unsigned long loose_count;
@@ -330,7 +601,7 @@ static int too_many_loose_objects(struct odb_source_files *files, int limit)
 	if (limit <= 0)
 		return 0;
 
-	if (odb_source_count_objects(&files->loose->base, ODB_COUNT_OBJECTS_APPROXIMATE,
+	if (odb_source_count_objects(&files->dirs->loose->base, ODB_COUNT_OBJECTS_APPROXIMATE,
 				     &loose_count) < 0)
 		return 0;
 
@@ -349,7 +620,7 @@ static struct packed_git *find_base_packs(struct odb_source_files *files,
 	struct packfile_list_entry *e;
 	struct packed_git *base = NULL;
 
-	for (e = packfile_store_get_packs(files->packed); e; e = e->next) {
+	for (e = packfile_store_get_packs(files->dirs->packed); e; e = e->next) {
 		if (e->pack->is_cruft)
 			continue;
 		if (limit) {
@@ -374,7 +645,7 @@ static int too_many_packs(struct odb_source_files *files, int gc_auto_pack_limit
 	if (gc_auto_pack_limit <= 0)
 		return 0;
 
-	for (e = packfile_store_get_packs(files->packed); e; e = e->next) {
+	for (e = packfile_store_get_packs(files->dirs->packed); e; e = e->next) {
 		if (e->pack->pack_keep)
 			continue;
 		/*
@@ -934,25 +1205,57 @@ static int odb_source_files_fsck(struct odb_source *source,
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	int ret = 0;
 
-	if (!(opts->flags & ODB_FSCK_FULL) && !source->local)
-		return 0;
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!(opts->flags & ODB_FSCK_FULL) && !dir->local)
+			continue;
 
-	ret |= odb_source_fsck(&files->loose->base, opts);
-	ret |= odb_source_fsck(&files->packed->base, opts);
+		ret |= odb_source_fsck(&dir->loose->base, opts);
+		ret |= odb_source_fsck(&dir->packed->base, opts);
+	}
 
 	return ret;
 }
 
+struct odb_files_dir *odb_source_files_find_dir(struct object_database *odb, const char *obj_dir)
+{
+	struct odb_source_files *files = odb_source_files_downcast(odb->source);
+	char *obj_dir_real = real_pathdup(obj_dir, 1);
+	struct strbuf odb_path_real = STRBUF_INIT;
+	struct odb_files_dir *dir;
+
+	for (dir = files->dirs; dir; dir = dir->next) {
+		strbuf_realpath(&odb_path_real, dir->abspath, 1);
+		if (!strcmp(obj_dir_real, odb_path_real.buf))
+			break;
+	}
+
+	free(obj_dir_real);
+	strbuf_release(&odb_path_real);
+	return dir;
+}
+
 struct odb_source_files *odb_source_files_new(struct object_database *odb,
-					      const char *path,
-					      bool local)
+					      enum odb_new_flags flags)
 {
 	struct odb_source_files *files;
+	char *object_dir = NULL;
+	char *alternates = NULL;
+
+	if (flags & ODB_NEW_HONOR_ENV) {
+		object_dir = xstrdup_or_null(getenv(DB_ENVIRONMENT));
+		alternates = xstrdup_or_null(getenv(ALTERNATE_DB_ENVIRONMENT));
+	}
+	if (!object_dir)
+		object_dir = xstrfmt("%s/objects", odb->repo->commondir);
 
 	CALLOC_ARRAY(files, 1);
-	odb_source_init(&files->base, odb, ODB_SOURCE_FILES, path, local);
-	files->loose = odb_source_loose_new(odb, path, local);
-	files->packed = odb_source_packed_new(odb, path, local);
+	odb_source_init(&files->base, odb, ODB_SOURCE_FILES, object_dir, true);
+
+	hashmap_init(&files->dirs_by_path, odb_files_dir_by_path_cmp, files, 0);
+	files->dirs_paths_icase = -1;
+
+	files->dirs = odb_files_dir_new(odb, object_dir, true);
+	files->dirs_tail = &files->dirs->next;
 
 	files->base.free = odb_source_files_free;
 	files->base.close = odb_source_files_close;
@@ -968,7 +1271,6 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->base.write_object = odb_source_files_write_object;
 	files->base.write_object_stream = odb_source_files_write_object_stream;
 	files->base.begin_transaction = odb_source_files_begin_transaction;
-	files->base.read_alternates = odb_source_files_read_alternates;
 	files->base.optimize = odb_source_files_optimize;
 	files->base.optimize_required = odb_source_files_optimize_required;
 	files->base.generate_pack = odb_source_files_generate_pack;
@@ -978,8 +1280,12 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	 * is not (yet) possible though because we access and assume relative
 	 * paths in the primary ODB source in some user-facing functionality.
 	 */
-	if (!is_absolute_path(path))
+	if (!is_absolute_path(object_dir))
 		chdir_notify_register(odb_source_files_reparent, files);
 
+	odb_prepare_alternates(files, alternates);
+
+	free(object_dir);
+	free(alternates);
 	return files;
 }

odb/source-files.h

@@ -6,20 +6,71 @@
 struct odb_source_loose;
 struct odb_source_packed;
 
+/*
+ * A single object directory that encapsulates access to both the loose and
+ * packed backend. This can either be the primary or an alternate object
+ * directory.
+ */
+struct odb_files_dir {
+	/* Absolute path to the object directory. */
+	char *abspath;
+
+	/* List of alternate object directories. */
+	struct odb_files_dir *next;
+
+	/*
+	 * Entry in the files source's map of directories, keyed by this
+	 * directory's path.
+	 */
+	struct hashmap_entry by_path_entry;
+
+	/* The two sources derived from this object directory. */
+	struct odb_source_loose *loose;
+	struct odb_source_packed *packed;
+
+	/*
+	 * Whether this is the local object directory of the owning
+	 * repository. Directories added via alternates are not local.
+	 */
+	bool local;
+};
+
+struct odb_files_dir *odb_files_dir_new(struct object_database *odb,
+					const char *path, bool local);
+void odb_files_dir_free(struct odb_files_dir *dir);
+
 /*
  * The files object database source uses a combination of loose objects and
  * packfiles. It is the default backend used by Git to store objects.
  */
 struct odb_source_files {
 	struct odb_source base;
-	struct odb_source_loose *loose;
-	struct odb_source_packed *packed;
+
+	/*
+	 * List of all object directories; the main directory is first (and
+	 * cannot be NULL after initialization). Subsequent directories are
+	 * alternates.
+	 */
+	struct odb_files_dir *dirs;
+	struct odb_files_dir **dirs_tail;
+
+	/*
+	 * Map of object directories, keyed by their respective paths. This
+	 * map is used to detect the case where the same directory is
+	 * registered multiple times.
+	 */
+	struct hashmap dirs_by_path;
+
+	/*
+	 * Whether directory paths shall be compared case-insensitively, as
+	 * determined by "core.ignoreCase".
+	 */
+	int dirs_paths_icase;
 };
 
 /* Allocate and initialize a new object source. */
 struct odb_source_files *odb_source_files_new(struct object_database *odb,
-					      const char *path,
-					      bool local);
+					      enum odb_new_flags flags);
 
 /*
  * Optimize the files object database source by repacking loose objects and
@@ -49,4 +100,10 @@ static inline struct odb_source_files *odb_source_files_downcast(struct odb_sour
 	return container_of(source, struct odb_source_files, base);
 }
 
+/*
+ * Find "files" directory by its object directory path. Returns a `NULL`
+ * pointer in case the object directory could not be found.
+ */
+struct odb_files_dir *odb_source_files_find_dir(struct object_database *odb, const char *obj_dir);
+
 #endif

odb/source-inmemory.c

@@ -322,12 +322,6 @@ static int odb_source_inmemory_begin_transaction(struct odb_source *source UNUSE
 	return error("in-memory source does not support transactions");
 }
 
-static int odb_source_inmemory_read_alternates(struct odb_source *source UNUSED,
-					       struct strvec *out UNUSED)
-{
-	return 0;
-}
-
 static void odb_source_inmemory_close(struct odb_source *source UNUSED)
 {
 }
@@ -390,7 +384,6 @@ struct odb_source_inmemory *odb_source_inmemory_new(struct object_database *odb)
 	source->base.write_object_stream = odb_source_inmemory_write_object_stream;
 	source->base.freshen_object = odb_source_inmemory_freshen_object;
 	source->base.begin_transaction = odb_source_inmemory_begin_transaction;
-	source->base.read_alternates = odb_source_inmemory_read_alternates;
 
 	return source;
 }

odb/source-loose.c

@@ -599,7 +599,7 @@ static int odb_source_loose_freshen_object(struct odb_source *source,
 static void close_loose_object(struct odb_source_loose *loose,
 			       int fd, const char *filename)
 {
-	if (loose->base.will_destroy)
+	if (loose->will_destroy)
 		goto out;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
@@ -985,12 +985,6 @@ static int odb_source_loose_begin_transaction(struct odb_source *source UNUSED,
 	return error("loose source does not support transactions");
 }
 
-static int odb_source_loose_read_alternates(struct odb_source *source UNUSED,
-					    struct strvec *out UNUSED)
-{
-	return 0;
-}
-
 static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
 {
 	oidtree_clear(loose->cache);
@@ -1145,7 +1139,6 @@ struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
 	loose->base.write_object = odb_source_loose_write_object;
 	loose->base.write_object_stream = odb_source_loose_write_object_stream;
 	loose->base.begin_transaction = odb_source_loose_begin_transaction;
-	loose->base.read_alternates = odb_source_loose_read_alternates;
 
 	if (!is_absolute_path(loose->base.path))
 		chdir_notify_register(odb_source_loose_reparent, loose);

odb/source-loose.h

@@ -28,6 +28,9 @@ struct odb_source_loose {
 
 	/* Map between object IDs for loose objects. */
 	struct loose_object_map *map;
+
+	/* Whether this is a source that will never be committed to disk. */
+	int will_destroy;
 };
 
 struct odb_source_loose *odb_source_loose_new(struct object_database *odb,

odb/source-packed.c

@@ -687,12 +687,6 @@ static int odb_source_packed_begin_transaction(struct odb_source *source UNUSED,
 	return error("packed backend cannot begin transactions");
 }
 
-static int odb_source_packed_read_alternates(struct odb_source *source UNUSED,
-					     struct strvec *out UNUSED)
-{
-	return 0;
-}
-
 void (*report_garbage)(unsigned seen_bits, const char *path);
 
 static void report_helper(const struct string_list *list,
@@ -1019,7 +1013,6 @@ struct odb_source_packed *odb_source_packed_new(struct object_database *odb,
 	packed->base.write_object = odb_source_packed_write_object;
 	packed->base.write_object_stream = odb_source_packed_write_object_stream;
 	packed->base.begin_transaction = odb_source_packed_begin_transaction;
-	packed->base.read_alternates = odb_source_packed_read_alternates;
 
 	if (!is_absolute_path(path))
 		chdir_notify_register(odb_source_packed_reparent, packed);

odb/source.c

@@ -24,10 +24,9 @@ const char *odb_source_type_to_name(enum odb_source_type type)
 }
 
 struct odb_source *odb_source_new(struct object_database *odb,
-				  const char *path,
-				  bool local)
+				  enum odb_new_flags flags)
 {
-	return &odb_source_files_new(odb, path, local)->base;
+	return &odb_source_files_new(odb, flags)->base;
 }
 
 void odb_source_init(struct odb_source *source,

odb/source.h

@@ -49,24 +49,9 @@ struct odb_create_on_disk_options {
 /*
  * The source is the part of the object database that stores the actual
  * objects. It thus encapsulates the logic to read and write the specific
- * on-disk format. An object database can have multiple sources:
- *
- *   - The primary source, which is typically located in "$GIT_DIR/objects".
- *     This is where new objects are usually written to.
- *
- *   - Alternate sources, which are configured via "objects/info/alternates" or
- *     via the GIT_ALTERNATE_OBJECT_DIRECTORIES environment variable. These
- *     alternate sources are only used to read objects.
+ * on-disk format.
  */
 struct odb_source {
-	struct odb_source *next;
-
-	/*
-	 * Entry in the object database's map of sources, keyed by this
-	 * source's path.
-	 */
-	struct hashmap_entry by_path_entry;
-
 	/* Object database that owns this object source. */
 	struct object_database *odb;
 
@@ -81,11 +66,6 @@ struct odb_source {
 	 */
 	bool local;
 
-	/*
-	 * This object store is ephemeral, so there is no need to fsync.
-	 */
-	int will_destroy;
-
 	/*
 	 * Path to the source. If this is a relative path, it is relative to
 	 * the current working directory.
@@ -278,19 +258,6 @@ struct odb_source {
 				 struct odb_transaction **out,
 				 enum odb_transaction_flags flags);
 
-	/*
-	 * This callback is expected to read the list of alternate object
-	 * database sources connected to it and write them into the `strvec`.
-	 *
-	 * The result is expected to be paths to the alternates. All paths must
-	 * be resolved to absolute paths.
-	 *
-	 * The callback is expected to return 0 on success, a negative error
-	 * code otherwise.
-	 */
-	int (*read_alternates)(struct odb_source *source,
-			       struct strvec *out);
-
 	/*
 	 * This callback is expected to optimize the object database source.
 	 * Returns 0 on success, a negative error code otherwise.
@@ -336,13 +303,11 @@ struct odb_source {
 };
 
 /*
- * Allocate and initialize a new source for the given object database located
- * at `path`. `local` indicates whether or not the source is the local and thus
- * primary object source of the object database.
+ * Allocate and initialize a new source for the given object database. The path
+ * of the source is derived from repository paths.
  */
 struct odb_source *odb_source_new(struct object_database *odb,
-				  const char *path,
-				  bool local);
+				  enum odb_new_flags flags);
 
 /*
  * Initialize the source for the given object database located at `path`.
@@ -529,20 +494,6 @@ static inline int odb_source_write_object_stream(struct odb_source *source,
 	return source->write_object_stream(source, stream, oid);
 }
 
-/*
- * Read the list of alternative object database sources from the given backend
- * and populate the `strvec` with them. The listing is not recursive -- that
- * is, if any of the yielded alternate sources has alternates itself, those
- * will not be yielded as part of this function call.
- *
- * Return 0 on success, a negative error code otherwise.
- */
-static inline int odb_source_read_alternates(struct odb_source *source,
-					     struct strvec *out)
-{
-	return source->read_alternates(source, out);
-}
-
 /*
  * Create a new transaction that can be used to write objects into a temporary
  * staging area. The objects will only be persisted when the transaction is

odb/streaming.c

@@ -182,12 +182,8 @@ static int istream_source(struct odb_stream **out,
 			  struct object_database *odb,
 			  const struct object_id *oid)
 {
-	struct odb_source *source;
-
-	for (source = odb->sources; source; source = source->next)
-		if (!odb_source_read_object_stream(out, source, oid))
-			return 0;
-
+	if (!odb_source_read_object_stream(out, odb->source, oid))
+		return 0;
 	return open_istream_incore(out, odb, oid);
 }
 

odb/transaction.c

@@ -12,7 +12,7 @@ int odb_transaction_begin(struct object_database *odb,
 	if (odb->transaction)
 		return error(_("object database transaction already pending"));
 
-	ret = odb_source_begin_transaction(odb->sources, out, flags);
+	ret = odb_source_begin_transaction(odb->source, out, flags);
 	if (!ret)
 		odb->transaction = *out;
 

pack-bitmap.c

@@ -712,15 +712,13 @@ static int open_bitmap_for_source(struct odb_source_packed *source,
 static int open_bitmap(struct repository *r,
 		       struct bitmap_index *bitmap_git)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	bool found = false;
 
 	assert(!bitmap_git->map);
 
-	for (source = r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-
-		if (!open_bitmap_for_source(files->packed, bitmap_git))
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!open_bitmap_for_source(dir->packed, bitmap_git))
 			found = true;
 
 		/*

packfile.c

@@ -273,14 +273,13 @@ static void scan_windows(struct packed_git *p,
 
 static int unuse_one_window(struct object_database *odb)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(odb->source);
 	struct packfile_list_entry *e;
 	struct packed_git *lru_p = NULL;
 	struct pack_window *lru_w = NULL, *lru_l = NULL;
 
-	for (source = odb->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		for (e = files->packed->packs.head; e; e = e->next)
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		for (e = dir->packed->packs.head; e; e = e->next)
 			scan_windows(e->pack, &lru_p, &lru_w, &lru_l);
 	}
 
@@ -440,15 +439,14 @@ static void find_lru_pack(struct packed_git *p, struct packed_git **lru_p, struc
 
 static int close_one_pack(struct repository *r)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	struct packfile_list_entry *e;
 	struct packed_git *lru_p = NULL;
 	struct pack_window *mru_w = NULL;
 	int accept_windows_inuse = 1;
 
-	for (source = r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		for (e = files->packed->packs.head; e; e = e->next) {
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		for (e = dir->packed->packs.head; e; e = e->next) {
 			if (e->pack->pack_fd == -1)
 				continue;
 			find_lru_pack(e->pack, &lru_p, &mru_w, &accept_windows_inuse);
@@ -1934,11 +1932,10 @@ struct packed_git **packfile_store_get_kept_pack_cache(struct odb_source_packed
 
 int has_object_pack(struct repository *r, const struct object_id *oid)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 
-	for (source = r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		if (!odb_source_read_object_info(&files->packed->base, oid, NULL, 0, NULL))
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		if (!odb_source_read_object_info(&dir->packed->base, oid, NULL, 0, NULL))
 			return 1;
 	}
 
@@ -1948,14 +1945,13 @@ int has_object_pack(struct repository *r, const struct object_id *oid)
 int has_object_kept_pack(struct repository *r, const struct object_id *oid,
 			 unsigned flags)
 {
-	struct odb_source *source;
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	struct pack_entry e;
 
-	for (source = r->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
 		struct packed_git **cache;
 
-		cache = packfile_store_get_kept_pack_cache(files->packed, flags);
+		cache = packfile_store_get_kept_pack_cache(dir->packed, flags);
 
 		for (; *cache; cache++) {
 			struct packed_git *p = *cache;

packfile.h

@@ -69,20 +69,20 @@ void packfile_store_add_pack(struct odb_source_packed *store,
 struct packfile_list_entry *packfile_store_get_packs(struct odb_source_packed *store);
 
 struct repo_for_each_pack_data {
-	struct odb_source *source;
+	struct odb_files_dir *dir;
 	struct packfile_list_entry *entry;
 };
 
 static inline struct repo_for_each_pack_data repo_for_eack_pack_data_init(struct repository *repo)
 {
 	struct repo_for_each_pack_data data = { 0 };
+	struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
 
-	for (struct odb_source *source = repo->objects->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		struct packfile_list_entry *entry = packfile_store_get_packs(files->packed);
+	for (struct odb_files_dir *dir = files->dirs; dir; dir = dir->next) {
+		struct packfile_list_entry *entry = packfile_store_get_packs(dir->packed);
 		if (!entry)
 			continue;
-		data.source = source;
+		data.dir = dir;
 		data.entry = entry;
 		break;
 	}
@@ -92,23 +92,22 @@ static inline struct repo_for_each_pack_data repo_for_eack_pack_data_init(struct
 
 static inline void repo_for_each_pack_data_next(struct repo_for_each_pack_data *data)
 {
-	struct odb_source *source;
+	struct odb_files_dir *dir;
 
 	data->entry = data->entry->next;
 	if (data->entry)
 		return;
 
-	for (source = data->source->next; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		struct packfile_list_entry *entry = packfile_store_get_packs(files->packed);
+	for (dir = data->dir->next; dir; dir = dir->next) {
+		struct packfile_list_entry *entry = packfile_store_get_packs(dir->packed);
 		if (!entry)
 			continue;
-		data->source = source;
+		data->dir = dir;
 		data->entry = entry;
 		return;
 	}
 
-	data->source = NULL;
+	data->dir = NULL;
 	data->entry = NULL;
 }
 

path.c

@@ -396,7 +396,7 @@ static void adjust_git_path(struct repository *repo,
 		strbuf_splice(buf, 0, buf->len,
 			      repo->index_file, strlen(repo->index_file));
 	else if (dir_prefix(base, "objects"))
-		replace_dir(buf, git_dir_len + 7, repo->objects->sources->path);
+		replace_dir(buf, git_dir_len + 7, repo->objects->source->path);
 	else if (repo_settings_get_hooks_path(repo) && dir_prefix(base, "hooks"))
 		replace_dir(buf, git_dir_len + 5, repo_settings_get_hooks_path(repo));
 	else if (repo->different_commondir)

prune-packed.c

@@ -40,7 +40,7 @@ void prune_packed_objects(int opts)
 		progress = start_delayed_progress(the_repository,
 						  _("Removing duplicate objects"), 256);
 
-	for_each_loose_file_in_source(the_repository->objects->sources,
+	for_each_loose_file_in_source(the_repository->objects->source,
 				      prune_object, NULL, prune_subdir, &opts);
 
 	/* Ensure we show 100% before finishing progress */

repack-geometry.c

@@ -33,7 +33,7 @@ void pack_geometry_init(struct pack_geometry *geometry,
 	struct packed_git *p;
 	struct strbuf buf = STRBUF_INIT;
 	struct odb_source_files *files = odb_source_files_downcast(existing->source);
-	struct multi_pack_index *m = get_multi_pack_index(files->packed);
+	struct multi_pack_index *m = get_multi_pack_index(files->dirs->packed);
 
 	repo_for_each_pack(existing->repo, p) {
 		if (geometry->midx_layer_threshold_set && m &&

repack-midx.c

@@ -564,7 +564,7 @@ static void repack_make_midx_append_plan(struct repack_write_midx_opts *opts,
 	size_t steps_nr = 0, steps_alloc = 0;
 
 	odb_reprepare(opts->existing->repo->objects);
-	m = get_multi_pack_index(files->packed);
+	m = get_multi_pack_index(files->dirs->packed);
 
 	if (opts->names->nr) {
 		struct strbuf buf = STRBUF_INIT;
@@ -620,7 +620,7 @@ static int repack_make_midx_compaction_plan(struct repack_write_midx_opts *opts,
 			    opts->existing->repo);
 
 	odb_reprepare(opts->existing->repo->objects);
-	m = get_multi_pack_index(files->packed);
+	m = get_multi_pack_index(files->dirs->packed);
 
 	for (i = 0; m && i < m->num_packs + m->num_packs_in_base; i++) {
 		if (prepare_midx_pack(m, i)) {
@@ -949,7 +949,7 @@ static int write_midx_incremental(struct repack_write_midx_opts *opts)
 	size_t i;
 	int ret = 0;
 
-	get_midx_chain_filename(files->packed, &lock_name);
+	get_midx_chain_filename(files->dirs->packed, &lock_name);
 	if (safe_create_leading_directories(opts->existing->repo,
 					    lock_name.buf))
 		die_errno(_("unable to create leading directories of %s"),

repack.c

@@ -59,8 +59,8 @@ void repack_remove_redundant_pack(struct repository *repo, const char *dir_name,
 				  bool wrote_incremental_midx)
 {
 	struct strbuf buf = STRBUF_INIT;
-	struct odb_source_files *files = odb_source_files_downcast(repo->objects->sources);
-	struct multi_pack_index *m = get_multi_pack_index(files->packed);
+	struct odb_source_files *files = odb_source_files_downcast(repo->objects->source);
+	struct multi_pack_index *m = get_multi_pack_index(files->dirs->packed);
 	strbuf_addf(&buf, "%s.pack", base_name);
 	if (m && files->base.local && midx_contains_pack(m, buf.buf)) {
 		clear_midx_file(repo);
@@ -158,7 +158,7 @@ void existing_packs_collect(struct existing_packs *existing,
 			string_list_append(&existing->non_kept_packs, buf.buf);
 	}
 
-	existing->source = existing->repo->objects->sources;
+	existing->source = existing->repo->objects->source;
 
 	string_list_sort(&existing->kept_packs);
 	string_list_sort(&existing->non_kept_packs);

repository.c

@@ -126,9 +126,9 @@ const char *repo_get_common_dir(struct repository *repo)
 
 const char *repo_get_object_directory(struct repository *repo)
 {
-	if (!repo->objects->sources)
+	if (!repo->objects->source)
 		BUG("repository hasn't been set up");
-	return repo->objects->sources->path;
+	return repo->objects->source->path;
 }
 
 const char *repo_get_index_file(struct repository *repo)

setup.c

@@ -2669,7 +2669,7 @@ void create_object_database(struct repository *repo,
 
 	repo->objects = odb_new(repo, ODB_NEW_HONOR_ENV);
 
-	if (odb_source_create_on_disk(repo->objects->sources, &opts) < 0)
+	if (odb_source_create_on_disk(repo->objects->source, &opts) < 0)
 		die(_("failed creating object database"));
 }
 

t/helper/test-read-graph.c

@@ -7,6 +7,7 @@
 #include "object-name.h"
 #include "repository.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "bloom.h"
 #include "setup.h"
 
@@ -80,11 +81,11 @@ int cmd__read_graph(int argc, const char **argv)
 	int ret = 0;
 
 	setup_git_directory(the_repository);
-	source = the_repository->objects->sources;
+	source = the_repository->objects->source;
 
 	prepare_repo_settings(the_repository);
 
-	graph = read_commit_graph_one(source);
+	graph = read_commit_graph_one(the_repository, source->path);
 	if (!graph) {
 		ret = 1;
 		goto done;

t/helper/test-read-midx.c

@@ -16,13 +16,13 @@ static struct multi_pack_index *setup_midx(const char *object_dir,
 					   struct odb_source_packed **out)
 {
 	struct odb_source_packed *packed;
-	struct odb_source *source;
+	struct odb_files_dir *dir;
 
 	setup_git_directory(the_repository);
 
-	source = odb_find_source(the_repository->objects, object_dir);
-	if (source) {
-		packed = odb_source_files_downcast(source)->packed;
+	dir = odb_source_files_find_dir(the_repository->objects, object_dir);
+	if (dir) {
+		packed = dir->packed;
 	} else {
 		packed = odb_source_packed_new(the_repository->objects,
 					       object_dir, false);

t/t4216-log-bloom.sh

@@ -755,7 +755,7 @@ test_expect_success PERL_TEST_HELPERS 'Bloom reader notices too-small data chunk
 test_expect_success PERL_TEST_HELPERS 'Bloom reader notices out-of-bounds filter offsets' '
 	check_corrupt_graph BIDX 12 FFFFFFFF &&
 	# use grep to avoid depending on exact chunk size
-	test_grep "warning: ignoring out-of-range offset (4294967295) for changed-path filter at pos 3 of .git/objects/info/commit-graph" err
+	test_grep "warning: ignoring out-of-range offset (4294967295) for changed-path filter at pos 3 of $(pwd)/.git/objects/info/commit-graph" err
 '
 
 test_expect_success PERL_TEST_HELPERS 'Bloom reader notices too-small index chunk' '
@@ -773,7 +773,7 @@ test_expect_success PERL_TEST_HELPERS 'Bloom reader notices out-of-order index o
 	# actually reading from the bogus offsets anyway.
 	corrupt_graph BIDX 4 0000000c00000005 &&
 	echo "warning: ignoring decreasing changed-path index offsets" \
-		"(12 > 5) for positions 1 and 2 of .git/objects/info/commit-graph" >expect.err &&
+		"(12 > 5) for positions 1 and 2 of $(pwd)/.git/objects/info/commit-graph" >expect.err &&
 	git -c core.commitGraph=false log -- A/B/file2 >expect.out &&
 	git -c core.commitGraph=true log -- A/B/file2 >out 2>err &&
 	test_cmp expect.out out &&

tmp-objdir.c

@@ -12,13 +12,16 @@
 #include "quote.h"
 #include "odb.h"
 #include "odb/source.h"
+#include "odb/source-files.h"
+#include "odb/source-loose.h"
 #include "repository.h"
 
 struct tmp_objdir {
 	struct repository *repo;
 	struct strbuf path;
 	struct strvec env;
-	struct odb_source *prev_source;
+	struct odb_files_dir *temp_dir;
+	struct odb_files_dir *orig_dir;
 	int will_destroy;
 };
 
@@ -51,6 +54,27 @@ static void tmp_objdir_reparent(const char *old_cwd,
 	free(path);
 }
 
+/*
+ * Restore the primary source that was previously replaced by
+ * `tmp_objdir_create()`.
+ */
+static void tmp_objdir_restore_source(struct tmp_objdir *t)
+{
+	struct odb_source_files *files = odb_source_files_downcast(t->repo->objects->source);
+	struct odb_files_dir *cur_dir = files->dirs;
+
+	if (t->temp_dir != files->dirs)
+		BUG("expected %s as primary object store; found %s",
+		    t->temp_dir->abspath, cur_dir->abspath);
+
+	if (t->temp_dir->next != t->orig_dir)
+		BUG("we expect the old primary object store to be the first alternate");
+
+	t->repo->disable_ref_updates = false;
+	files->dirs = t->orig_dir;
+	odb_files_dir_free(cur_dir);
+}
+
 int tmp_objdir_destroy(struct tmp_objdir *t)
 {
 	int err;
@@ -61,8 +85,8 @@ int tmp_objdir_destroy(struct tmp_objdir *t)
 	if (t == the_tmp_objdir)
 		the_tmp_objdir = NULL;
 
-	if (t->prev_source)
-		odb_restore_primary_source(t->repo->objects, t->prev_source, t->path.buf);
+	if (t->orig_dir)
+		tmp_objdir_restore_source(t);
 
 	err = remove_dir_recursively(&t->path, 0);
 
@@ -132,8 +156,10 @@ static int setup_tmp_objdir(const char *root)
 }
 
 struct tmp_objdir *tmp_objdir_create(struct repository *r,
-				     const char *prefix)
+				     const char *prefix,
+				     int will_destroy)
 {
+	struct odb_source_files *files = odb_source_files_downcast(r->objects->source);
 	static int installed_handlers;
 	struct tmp_objdir *t;
 
@@ -142,6 +168,7 @@ struct tmp_objdir *tmp_objdir_create(struct repository *r,
 
 	t = xcalloc(1, sizeof(*t));
 	t->repo = r;
+	t->will_destroy = will_destroy;
 	strbuf_init(&t->path, 0);
 	strvec_init(&t->env);
 
@@ -179,6 +206,19 @@ struct tmp_objdir *tmp_objdir_create(struct repository *r,
 	env_replace(&t->env, GIT_QUARANTINE_ENVIRONMENT,
 		    absolute_path(t->path.buf));
 
+	/*
+	 * Make a new primary source and link the old primary source in as an
+	 * alternate. Disable ref updates while a temporary source is active,
+	 * since the objects in the database may roll back.
+	 */
+	t->temp_dir = odb_files_dir_new(t->repo->objects, t->path.buf, false);
+	t->temp_dir->loose->will_destroy = will_destroy;
+	t->temp_dir->next = files->dirs;
+
+	t->orig_dir = files->dirs;
+	files->dirs = t->temp_dir;
+	t->repo->disable_ref_updates = true;
+
 	return t;
 }
 
@@ -295,11 +335,11 @@ int tmp_objdir_migrate(struct tmp_objdir *t)
 	if (!t)
 		return 0;
 
-	if (t->prev_source) {
-		if (t->repo->objects->sources->will_destroy)
+	if (t->orig_dir) {
+		if (t->will_destroy)
 			BUG("migrating an ODB that was marked for destruction");
-		odb_restore_primary_source(t->repo->objects, t->prev_source, t->path.buf);
-		t->prev_source = NULL;
+		tmp_objdir_restore_source(t);
+		t->orig_dir = NULL;
 	}
 
 	strbuf_addbuf(&src, &t->path);
@@ -320,14 +360,3 @@ const char **tmp_objdir_env(const struct tmp_objdir *t)
 		return NULL;
 	return t->env.v;
 }
-
-struct odb_source *tmp_objdir_replace_primary_odb(struct tmp_objdir *t,
-						  int will_destroy)
-{
-	if (t->prev_source)
-		BUG("the primary object database is already replaced");
-	t->will_destroy = will_destroy;
-
-	return odb_set_temporary_primary_source(t->repo->objects, t->path.buf,
-						will_destroy, &t->prev_source);
-}

tmp-objdir.h

@@ -11,7 +11,7 @@
  * Example:
  *
  *	struct child_process child = CHILD_PROCESS_INIT;
- *	struct tmp_objdir *t = tmp_objdir_create(repo, "incoming");
+ *	struct tmp_objdir *t = tmp_objdir_create(repo, "incoming", 0);
  *	strvec_push(&child.args, cmd);
  *	strvec_pushv(&child.env, tmp_objdir_env(t));
  *	if (!run_command(&child)) && !tmp_objdir_migrate(t))
@@ -25,10 +25,11 @@ struct repository;
 struct tmp_objdir;
 
 /*
- * Create a new temporary object directory with the specified prefix;
- * returns NULL on failure.
+ * Create a new temporary object directory with the specified prefix and
+ * install the directory as the primary write target; returns NULL on failure.
  */
-struct tmp_objdir *tmp_objdir_create(struct repository *r, const char *prefix);
+struct tmp_objdir *tmp_objdir_create(struct repository *r, const char *prefix,
+				     int will_destroy);
 
 /*
  * Return a list of environment strings, suitable for use with
@@ -55,13 +56,4 @@ int tmp_objdir_destroy(struct tmp_objdir *);
  */
 void tmp_objdir_discard_objects(struct tmp_objdir *);
 
-/*
- * Replaces the writable object store in the current process with the temporary
- * object directory and makes the former main object store an alternate.
- * If will_destroy is nonzero, the object directory may not be migrated. Returns
- * the newly installed primary source.
- */
-struct odb_source *tmp_objdir_replace_primary_odb(struct tmp_objdir *,
-						  int will_destroy);
-
 #endif /* TMP_OBJDIR_H */