patch, 11 partsAdd initial remote odb support

Makefile, odb-helper.c, odb-helper.h, remote-odb.c, remote-odb.h

diff --git a/Makefile b/Makefile
index e4b503d259..8465e3ccd4 100644
--- a/Makefile
+++ b/Makefile
@@ -896,6 +896,8 @@ LIB_OBJS += notes-cache.o
 LIB_OBJS += notes-merge.o
 LIB_OBJS += notes-utils.o
 LIB_OBJS += object.o
+LIB_OBJS += odb-helper.o
+LIB_OBJS += remote-odb.o
 LIB_OBJS += oidmap.o
 LIB_OBJS += oidset.o
 LIB_OBJS += packfile.o
diff --git a/odb-helper.c b/odb-helper.c
new file mode 100644
index 0000000000..b4d403ffa9
--- /dev/null
+++ b/odb-helper.c
@@ -0,0 +1,16 @@
+#include "cache.h"
+#include "object.h"
+#include "argv-array.h"
+#include "odb-helper.h"
+#include "run-command.h"
+#include "sha1-lookup.h"
+
+struct odb_helper *odb_helper_new(const char *name, int namelen)
+{
+	struct odb_helper *o;
+
+	o = xcalloc(1, sizeof(*o));
+	o->name = xmemdupz(name, namelen);
+
+	return o;
+}
diff --git a/odb-helper.h b/odb-helper.h
new file mode 100644
index 0000000000..4b792a3896
--- /dev/null
+++ b/odb-helper.h
@@ -0,0 +1,19 @@
+#ifndef ODB_HELPER_H
+#define ODB_HELPER_H
+
+/*
+ * An odb helper is a way to access a remote odb.
+ *
+ * Information in its fields comes from the config file [odb "NAME"]
+ * entries.
+ */
+struct odb_helper {
+	const char *name;                 /* odb.<NAME>.* */
+	const char *remote;               /* odb.<NAME>.promisorRemote */
+
+	struct odb_helper *next;
+};
+
+extern struct odb_helper *odb_helper_new(const char *name, int namelen);
+
+#endif /* ODB_HELPER_H */
diff --git a/remote-odb.c b/remote-odb.c
new file mode 100644
index 0000000000..1dc165eaf6
--- /dev/null
+++ b/remote-odb.c
@@ -0,0 +1,72 @@
+#include "cache.h"
+#include "remote-odb.h"
+#include "odb-helper.h"
+#include "config.h"
+
+static struct odb_helper *helpers;
+static struct odb_helper **helpers_tail = &helpers;
+
+static struct odb_helper *find_or_create_helper(const char *name, int len)
+{
+	struct odb_helper *o;
+
+	for (o = helpers; o; o = o->next)
+		if (!strncmp(o->name, name, len) && !o->name[len])
+			return o;
+
+	o = odb_helper_new(name, len);
+	*helpers_tail = o;
+	helpers_tail = &o->next;
+
+	return o;
+}
+
+static int remote_odb_config(const char *var, const char *value, void *data)
+{
+	struct odb_helper *o;
+	const char *name;
+	int namelen;
+	const char *subkey;
+
+	if (parse_config_key(var, "odb", &name, &namelen, &subkey) < 0)
+		return 0;
+
+	o = find_or_create_helper(name, namelen);
+
+	if (!strcmp(subkey, "promisorremote"))
+		return git_config_string(&o->remote, var, value);
+
+	return 0;
+}
+
+static void remote_odb_init(void)
+{
+	static int initialized;
+
+	if (initialized)
+		return;
+	initialized = 1;
+
+	git_config(remote_odb_config, NULL);
+}
+
+struct odb_helper *find_odb_helper(const char *remote)
+{
+	struct odb_helper *o;
+
+	remote_odb_init();
+
+	if (!remote)
+		return helpers;
+
+	for (o = helpers; o; o = o->next)
+		if (!strcmp(o->remote, remote))
+			return o;
+
+	return NULL;
+}
+
+int has_remote_odb(void)
+{
+	return !!find_odb_helper(NULL);
+}
diff --git a/remote-odb.h b/remote-odb.h
new file mode 100644
index 0000000000..4c7b13695f
--- /dev/null
+++ b/remote-odb.h
@@ -0,0 +1,7 @@
+#ifndef REMOTE_ODB_H
+#define REMOTE_ODB_H
+
+extern struct odb_helper *find_odb_helper(const char *remote);
+extern int has_remote_odb(void);
+
+#endif /* REMOTE_ODB_H */

odb-helper.c, odb-helper.h, remote-odb.c, remote-odb.h

diff --git a/odb-helper.c b/odb-helper.c
index 99b5a345e8..246ebf8f7a 100644
--- a/odb-helper.c
+++ b/odb-helper.c
@@ -28,3 +28,18 @@ int odb_helper_get_direct(struct odb_helper *o,
 
 	return res;
 }
+
+int odb_helper_get_many_direct(struct odb_helper *o,
+			       const struct oid_array *to_get)
+{
+	int res;
+	uint64_t start;
+
+	start = getnanotime();
+
+	res = fetch_objects(o->remote, to_get);
+
+	trace_performance_since(start, "odb_helper_get_many_direct");
+
+	return res;
+}
diff --git a/odb-helper.h b/odb-helper.h
index 4c52e81ce8..154ce4c7e4 100644
--- a/odb-helper.h
+++ b/odb-helper.h
@@ -17,4 +17,7 @@ struct odb_helper {
 extern struct odb_helper *odb_helper_new(const char *name, int namelen);
 extern int odb_helper_get_direct(struct odb_helper *o,
 				 const unsigned char *sha1);
+extern int odb_helper_get_many_direct(struct odb_helper *o,
+				      const struct oid_array *to_get);
+
 #endif /* ODB_HELPER_H */
diff --git a/remote-odb.c b/remote-odb.c
index a34537c05c..cc7059b23a 100644
--- a/remote-odb.c
+++ b/remote-odb.c
@@ -87,3 +87,20 @@ int remote_odb_get_direct(const unsigned char *sha1)
 
 	return -1;
 }
+
+int remote_odb_get_many_direct(const struct oid_array *to_get)
+{
+	struct odb_helper *o;
+
+	trace_printf("trace: remote_odb_get_many_direct: nr: %d", to_get->nr);
+
+	remote_odb_init();
+
+	for (o = helpers; o; o = o->next) {
+		if (odb_helper_get_many_direct(o, to_get) < 0)
+			continue;
+		return 0;
+	}
+
+	return -1;
+}
diff --git a/remote-odb.h b/remote-odb.h
index c5384c922d..e10a8bf855 100644
--- a/remote-odb.h
+++ b/remote-odb.h
@@ -4,5 +4,6 @@
 extern struct odb_helper *find_odb_helper(const char *remote);
 extern int has_remote_odb(void);
 extern int remote_odb_get_direct(const unsigned char *sha1);
+extern int remote_odb_get_many_direct(const struct oid_array *to_get);
 
 #endif /* REMOTE_ODB_H */

builtin/fetch.c, list-objects-filter-options.c, list-objects-filter-options.h, odb-helper.h, remote-odb.c, t/t5616-partial-clone.sh

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 1fd4dfd024..52ec2fd200 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1343,7 +1343,7 @@ static inline void fetch_one_setup_partial(struct remote *remote)
 	 * the config.
 	 */
 	if (!filter_options.choice)
-		partial_clone_get_default_filter_spec(&filter_options);
+		partial_clone_get_default_filter_spec(&filter_options, remote->name);
 	return;
 }
 
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 8e7b9ae776..755a793664 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -7,6 +7,7 @@
 #include "list-objects-filter.h"
 #include "list-objects-filter-options.h"
 #include "remote-odb.h"
+#include "odb-helper.h"
 
 /*
  * Parse value of the argument to the "filter" keyword.
@@ -29,6 +30,9 @@ static int gently_parse_list_objects_filter(
 {
 	const char *v0;
 
+	if (!arg)
+		return 0;
+
 	if (filter_options->choice) {
 		if (errbuf) {
 			strbuf_init(errbuf, 0);
@@ -116,6 +120,7 @@ void partial_clone_register(
 	const struct list_objects_filter_options *filter_options)
 {
 	char *cfg_name;
+	char *filter_name;
 
 	/* Check if it is already registered */
 	if (find_odb_helper(remote))
@@ -131,25 +136,26 @@ void partial_clone_register(
 	/*
 	 * Record the initial filter-spec in the config as
 	 * the default for subsequent fetches from this remote.
-	 *
-	 * TODO: move core.partialclonefilter into odb.<name>
 	 */
-	core_partial_clone_filter_default =
-		xstrdup(filter_options->filter_spec);
-	git_config_set("core.partialclonefilter",
-		       core_partial_clone_filter_default);
+	filter_name = xstrfmt("odb.%s.partialclonefilter", remote);
+	git_config_set(filter_name, filter_options->filter_spec);
+	free(filter_name);
 
 	/* Make sure the config info are reset */
 	remote_odb_reinit();
 }
 
 void partial_clone_get_default_filter_spec(
-	struct list_objects_filter_options *filter_options)
+	struct list_objects_filter_options *filter_options,
+	const char *remote)
 {
+	struct odb_helper *helper = find_odb_helper(remote);
+
 	/*
 	 * Parse default value, but silently ignore it if it is invalid.
 	 */
-	gently_parse_list_objects_filter(filter_options,
-					 core_partial_clone_filter_default,
-					 NULL);
+	if (helper)
+		gently_parse_list_objects_filter(filter_options,
+						 helper->partial_clone_filter,
+						 NULL);
 }
diff --git a/list-objects-filter-options.h b/list-objects-filter-options.h
index 0000a61f82..12ceef3230 100644
--- a/list-objects-filter-options.h
+++ b/list-objects-filter-options.h
@@ -74,6 +74,7 @@ void partial_clone_register(
 	const char *remote,
 	const struct list_objects_filter_options *filter_options);
 void partial_clone_get_default_filter_spec(
-	struct list_objects_filter_options *filter_options);
+	struct list_objects_filter_options *filter_options,
+	const char *remote);
 
 #endif /* LIST_OBJECTS_FILTER_OPTIONS_H */
diff --git a/odb-helper.h b/odb-helper.h
index 154ce4c7e4..4af75ef55c 100644
--- a/odb-helper.h
+++ b/odb-helper.h
@@ -10,6 +10,7 @@
 struct odb_helper {
 	const char *name;                 /* odb.<NAME>.* */
 	const char *remote;               /* odb.<NAME>.promisorRemote */
+	const char *partial_clone_filter; /* odb.<NAME>.partialCloneFilter */
 
 	struct odb_helper *next;
 };
diff --git a/remote-odb.c b/remote-odb.c
index 2b93d13abd..5b9d1930b5 100644
--- a/remote-odb.c
+++ b/remote-odb.c
@@ -35,6 +35,8 @@ static int remote_odb_config(const char *var, const char *value, void *data)
 
 	if (!strcmp(subkey, "promisorremote"))
 		return git_config_string(&o->remote, var, value);
+	if (!strcmp(subkey, "partialclonefilter"))
+		return git_config_string(&o->partial_clone_filter, var, value);
 
 	return 0;
 }
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 5ddd1e011c..4231121181 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -41,7 +41,7 @@ test_expect_success 'do partial clone 1' '
 	test_cmp expect_1.oids observed.oids &&
 	test "$(git -C pc1 config --local core.repositoryformatversion)" = "1" &&
 	test "$(git -C pc1 config --local odb.origin.promisorRemote)" = "origin" &&
-	test "$(git -C pc1 config --local core.partialclonefilter)" = "blob:none"
+	test "$(git -C pc1 config --local odb.origin.partialclonefilter)" = "blob:none"
 '
 
 # checkout master to force dynamic object fetch of blobs at HEAD.

builtin/cat-file.c, builtin/fetch.c, builtin/gc.c, builtin/repack.c, cache.h, connected.c, environment.c, list-objects-filter-options.c, packfile.c, setup.c, sha1-file.c, t/t0410-partial-clone.sh, t/t5500-fetch-pack.sh, t/t5601-clone.sh, t/t5616-partial-clone.sh, unpack-trees.c

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 665b581949..3b24c1b9b7 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -13,6 +13,7 @@
 #include "tree-walk.h"
 #include "sha1-array.h"
 #include "packfile.h"
+#include "remote-odb.h"
 
 struct batch_options {
 	int enabled;
@@ -477,8 +478,8 @@ static int batch_objects(struct batch_options *opt)
 
 		for_each_loose_object(batch_loose_object, &sa, 0);
 		for_each_packed_object(batch_packed_object, &sa, 0);
-		if (repository_format_partial_clone)
-			warning("This repository has extensions.partialClone set. Some objects may not be loaded.");
+		if (has_remote_odb())
+			warning("This repository uses an odb. Some objects may not be loaded.");
 
 		cb.opt = opt;
 		cb.expand = &data;
diff --git a/builtin/fetch.c b/builtin/fetch.c
index ea5b9669ad..1fd4dfd024 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -21,6 +21,7 @@
 #include "utf8.h"
 #include "packfile.h"
 #include "list-objects-filter-options.h"
+#include "remote-odb.h"
 
 static const char * const builtin_fetch_usage[] = {
 	N_("git fetch [<options>] [<repository> [<refspec>...]]"),
@@ -1313,7 +1314,7 @@ static inline void fetch_one_setup_partial(struct remote *remote)
 	 * If no prior partial clone/fetch and the current fetch DID NOT
 	 * request a partial-fetch, do a normal fetch.
 	 */
-	if (!repository_format_partial_clone && !filter_options.choice)
+	if (!has_remote_odb() && !filter_options.choice)
 		return;
 
 	/*
@@ -1321,7 +1322,7 @@ static inline void fetch_one_setup_partial(struct remote *remote)
 	 * on this repo and remember the given filter-spec as the default
 	 * for subsequent fetches to this remote.
 	 */
-	if (!repository_format_partial_clone && filter_options.choice) {
+	if (!has_remote_odb() && filter_options.choice) {
 		partial_clone_register(remote->name, &filter_options);
 		return;
 	}
@@ -1330,7 +1331,7 @@ static inline void fetch_one_setup_partial(struct remote *remote)
 	 * We are currently limited to only ONE promisor remote and only
 	 * allow partial-fetches from the promisor remote.
 	 */
-	if (strcmp(remote->name, repository_format_partial_clone)) {
+	if (!find_odb_helper(remote->name)) {
 		if (filter_options.choice)
 			die(_("--filter can only be used with the remote configured in core.partialClone"));
 		return;
@@ -1461,7 +1462,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (depth || deepen_since || deepen_not.nr)
 		deepen = 1;
 
-	if (filter_options.choice && !repository_format_partial_clone)
+	if (filter_options.choice && !has_remote_odb())
 		die("--filter can only be used when extensions.partialClone is set");
 
 	if (all) {
@@ -1495,7 +1496,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	}
 
 	if (remote) {
-		if (filter_options.choice || repository_format_partial_clone)
+		if (filter_options.choice || has_remote_odb())
 			fetch_one_setup_partial(remote);
 		result = fetch_one(remote, argc, argv, prune_tags_ok);
 	} else {
diff --git a/builtin/gc.c b/builtin/gc.c
index ccfb1ceaeb..02c783b514 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -26,6 +26,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "remote-odb.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -619,7 +620,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			argv_array_push(&prune, prune_expire);
 			if (quiet)
 				argv_array_push(&prune, "--no-progress");
-			if (repository_format_partial_clone)
+			if (has_remote_odb())
 				argv_array_push(&prune,
 						"--exclude-promisor-objects");
 			if (run_command_v_opt(prune.argv, RUN_GIT_CMD))
diff --git a/builtin/repack.c b/builtin/repack.c
index 6c636e159e..72b1e2d94f 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -8,6 +8,7 @@
 #include "strbuf.h"
 #include "string-list.h"
 #include "argv-array.h"
+#include "remote-odb.h"
 
 static int delta_base_offset = 1;
 static int pack_kept_objects = -1;
@@ -249,7 +250,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	argv_array_push(&cmd.args, "--all");
 	argv_array_push(&cmd.args, "--reflog");
 	argv_array_push(&cmd.args, "--indexed-objects");
-	if (repository_format_partial_clone)
+	if (has_remote_odb())
 		argv_array_push(&cmd.args, "--exclude-promisor-objects");
 	if (window)
 		argv_array_pushf(&cmd.args, "--window=%s", window);
diff --git a/cache.h b/cache.h
index 89a107a7f7..2855435798 100644
--- a/cache.h
+++ b/cache.h
@@ -904,13 +904,11 @@ extern int grafts_replace_parents;
 #define GIT_REPO_VERSION 0
 #define GIT_REPO_VERSION_READ 1
 extern int repository_format_precious_objects;
-extern char *repository_format_partial_clone;
 extern const char *core_partial_clone_filter_default;
 
 struct repository_format {
 	int version;
 	int precious_objects;
-	char *partial_clone; /* value of extensions.partialclone */
 	int is_bare;
 	int hash_algo;
 	char *work_tree;
diff --git a/connected.c b/connected.c
index 91feb78815..07154a358d 100644
--- a/connected.c
+++ b/connected.c
@@ -4,6 +4,7 @@
 #include "connected.h"
 #include "transport.h"
 #include "packfile.h"
+#include "remote-odb.h"
 
 /*
  * If we feed all the commits we want to verify to this command
@@ -56,7 +57,7 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 	argv_array_push(&rev_list.args,"rev-list");
 	argv_array_push(&rev_list.args, "--objects");
 	argv_array_push(&rev_list.args, "--stdin");
-	if (repository_format_partial_clone)
+	if (has_remote_odb())
 		argv_array_push(&rev_list.args, "--exclude-promisor-objects");
 	argv_array_push(&rev_list.args, "--not");
 	argv_array_push(&rev_list.args, "--all");
diff --git a/environment.c b/environment.c
index 2a6de2330b..f8048f4a5d 100644
--- a/environment.c
+++ b/environment.c
@@ -30,7 +30,6 @@ int warn_ambiguous_refs = 1;
 int warn_on_object_refname_ambiguity = 1;
 int ref_paranoia = -1;
 int repository_format_precious_objects;
-char *repository_format_partial_clone;
 const char *core_partial_clone_filter_default;
 const char *git_commit_encoding;
 const char *git_log_output_encoding;
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 6a3cc985c4..8e7b9ae776 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -6,6 +6,7 @@
 #include "list-objects.h"
 #include "list-objects-filter.h"
 #include "list-objects-filter-options.h"
+#include "remote-odb.h"
 
 /*
  * Parse value of the argument to the "filter" keyword.
@@ -114,30 +115,32 @@ void partial_clone_register(
 	const char *remote,
 	const struct list_objects_filter_options *filter_options)
 {
-	/*
-	 * Record the name of the partial clone remote in the
-	 * config and in the global variable -- the latter is
-	 * used throughout to indicate that partial clone is
-	 * enabled and to expect missing objects.
-	 */
-	if (repository_format_partial_clone &&
-	    *repository_format_partial_clone &&
-	    strcmp(remote, repository_format_partial_clone))
-		die(_("cannot change partial clone promisor remote"));
+	char *cfg_name;
+
+	/* Check if it is already registered */
+	if (find_odb_helper(remote))
+		return;
 
 	git_config_set("core.repositoryformatversion", "1");
-	git_config_set("extensions.partialclone", remote);
 
-	repository_format_partial_clone = xstrdup(remote);
+	/* Add odb config for the remote */
+	cfg_name = xstrfmt("odb.%s.promisorRemote", remote);
+	git_config_set(cfg_name, remote);
+	free(cfg_name);
 
 	/*
 	 * Record the initial filter-spec in the config as
 	 * the default for subsequent fetches from this remote.
+	 *
+	 * TODO: move core.partialclonefilter into odb.<name>
 	 */
 	core_partial_clone_filter_default =
 		xstrdup(filter_options->filter_spec);
 	git_config_set("core.partialclonefilter",
 		       core_partial_clone_filter_default);
+
+	/* Make sure the config info are reset */
+	remote_odb_reinit();
 }
 
 void partial_clone_get_default_filter_spec(
diff --git a/packfile.c b/packfile.c
index 7cd45aa4b2..9cbc974612 100644
--- a/packfile.c
+++ b/packfile.c
@@ -15,6 +15,7 @@
 #include "tree-walk.h"
 #include "tree.h"
 #include "object-store.h"
+#include "remote-odb.h"
 
 char *odb_pack_name(struct strbuf *buf,
 		    const unsigned char *sha1,
@@ -1976,7 +1977,7 @@ int is_promisor_object(const struct object_id *oid)
 	static int promisor_objects_prepared;
 
 	if (!promisor_objects_prepared) {
-		if (repository_format_partial_clone) {
+		if (has_remote_odb()) {
 			for_each_packed_object(add_promisor_object,
 					       &promisor_objects,
 					       FOR_EACH_OBJECT_PROMISOR_ONLY);
diff --git a/setup.c b/setup.c
index b24c811c1c..4eeb7fe073 100644
--- a/setup.c
+++ b/setup.c
@@ -419,11 +419,7 @@ static int check_repo_format(const char *var, const char *value, void *vdata)
 			;
 		else if (!strcmp(ext, "preciousobjects"))
 			data->precious_objects = git_config_bool(var, value);
-		else if (!strcmp(ext, "partialclone")) {
-			if (!value)
-				return config_error_nonbool(var);
-			data->partial_clone = xstrdup(value);
-		} else
+		else
 			string_list_append(&data->unknown_extensions, ext);
 	} else if (strcmp(var, "core.bare") == 0) {
 		data->is_bare = git_config_bool(var, value);
@@ -465,7 +461,6 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 	}
 
 	repository_format_precious_objects = candidate->precious_objects;
-	repository_format_partial_clone = candidate->partial_clone;
 	string_list_clear(&candidate->unknown_extensions, 0);
 	if (!has_common) {
 		if (candidate->is_bare != -1) {
diff --git a/sha1-file.c b/sha1-file.c
index 374a56d0e1..1fb95790de 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -32,6 +32,7 @@
 #include "packfile.h"
 #include "fetch-object.h"
 #include "object-store.h"
+#include "remote-odb.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -1309,15 +1310,16 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 		}
 
 		/* Check if it is a missing object */
-		if (fetch_if_missing && repository_format_partial_clone &&
+		if (fetch_if_missing && has_remote_odb() &&
 		    !already_retried && r == the_repository) {
 			/*
-			 * TODO Investigate checking fetch_object() return
-			 * TODO value and stopping on error here.
-			 * TODO Pass a repository struct through fetch_object,
-			 * such that arbitrary repositories work.
+			 * TODO Investigate checking remote_odb_get_direct()
+			 * TODO return value and stopping on error here.
+			 * TODO Pass a repository struct through
+			 * remote_odb_get_direct(), such that arbitrary
+			 * repositories work.
 			 */
-			fetch_object(repository_format_partial_clone, real->hash);
+			remote_odb_get_direct(real->hash);
 			already_retried = 1;
 			continue;
 		}
diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index cc18b75c03..6af4712da8 100755
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -43,7 +43,7 @@ test_expect_success 'missing reflog object, but promised by a commit, passes fsc
 
 	# But with the extension, it succeeds
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo fsck
 '
 
@@ -66,7 +66,7 @@ test_expect_success 'missing reflog object, but promised by a tag, passes fsck'
 	printf "$T\n" | pack_as_from_promisor &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo fsck
 '
 
@@ -84,7 +84,7 @@ test_expect_success 'missing reflog object alone fails fsck, even with extension
 	delete_object repo "$A" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	test_must_fail git -C repo fsck
 '
 
@@ -100,7 +100,7 @@ test_expect_success 'missing ref object, but promised, passes fsck' '
 	promise_and_delete "$A" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo fsck
 '
 
@@ -123,7 +123,7 @@ test_expect_success 'missing object, but promised, passes fsck' '
 	promise_and_delete "$AT" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo fsck
 '
 
@@ -136,7 +136,7 @@ test_expect_success 'missing CLI object, but promised, passes fsck' '
 	promise_and_delete "$A" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo fsck "$A"
 '
 
@@ -151,7 +151,7 @@ test_expect_success 'fetching of missing objects' '
 	rm -rf repo/.git/objects/* &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "origin" &&
+	git -C repo config odb.magic.promisorRemote "origin" &&
 	git -C repo cat-file -p "$HASH" &&
 
 	# Ensure that the .promisor file is written, and check that its
@@ -172,7 +172,7 @@ test_expect_success 'rev-list stops traversal at missing and promised commit' '
 	promise_and_delete "$FOO" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo rev-list --exclude-promisor-objects --objects bar >out &&
 	grep $(git -C repo rev-parse bar) out &&
 	! grep $FOO out
@@ -197,7 +197,7 @@ test_expect_success 'rev-list stops traversal at missing and promised tree' '
 	promise_and_delete "$TREE2" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo rev-list --exclude-promisor-objects --objects HEAD >out &&
 	grep $(git -C repo rev-parse foo) out &&
 	! grep $TREE out &&
@@ -216,7 +216,7 @@ test_expect_success 'rev-list stops traversal at missing and promised blob' '
 	promise_and_delete "$BLOB" &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo rev-list --exclude-promisor-objects --objects HEAD >out &&
 	grep $(git -C repo rev-parse HEAD) out &&
 	! grep $BLOB out
@@ -235,7 +235,7 @@ test_expect_success 'rev-list stops traversal at promisor commit, tree, and blob
 	printf "%s\n%s\n%s\n" $COMMIT $TREE $BLOB | pack_as_from_promisor &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo rev-list --exclude-promisor-objects --objects HEAD >out &&
 	! grep $COMMIT out &&
 	! grep $TREE out &&
@@ -259,7 +259,7 @@ test_expect_success 'rev-list accepts missing and promised objects on command li
 	promise_and_delete $BLOB &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo rev-list --exclude-promisor-objects --objects "$COMMIT" "$TREE" "$BLOB"
 '
 
@@ -272,7 +272,7 @@ test_expect_success 'gc does not repack promisor objects' '
 	HASH=$(printf "$TREE_HASH\n" | pack_as_from_promisor) &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo gc &&
 
 	# Ensure that the promisor packfile still exists, and remove it
@@ -296,7 +296,7 @@ test_expect_success 'gc stops traversal when a missing but promised object is re
 	HASH=$(promise_and_delete $TREE_HASH) &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "arbitrary string" &&
+	git -C repo config odb.magic.promisorRemote "arbitrary string" &&
 	git -C repo gc &&
 
 	# Ensure that the promisor packfile still exists, and remove it
@@ -327,7 +327,7 @@ test_expect_success 'fetching of missing objects from an HTTP server' '
 	rm -rf repo/.git/objects/* &&
 
 	git -C repo config core.repositoryformatversion 1 &&
-	git -C repo config extensions.partialclone "origin" &&
+	git -C repo config odb.magic.promisorRemote "origin" &&
 	git -C repo cat-file -p "$HASH" &&
 
 	# Ensure that the .promisor file is written, and check that its
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index d4f435155f..d57fa2dbe4 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -792,14 +792,14 @@ fetch_filter_blob_limit_zero () {
 	test_config -C "$SERVER" uploadpack.allowfilter 1 &&
 
 	git clone "$URL" client &&
-	test_config -C client extensions.partialclone origin &&
+	test_config -C client odb.magic.promisorRemote origin &&
 
 	test_commit -C "$SERVER" two &&
 
 	git -C client fetch --filter=blob:limit=0 origin HEAD:somewhere &&
 
 	# Ensure that commit is fetched, but blob is not
-	test_config -C client extensions.partialclone "arbitrary string" &&
+	test_config -C client odb.magic.promisorRemote "arbitrary string" &&
 	git -C client cat-file -e $(git -C "$SERVER" rev-parse two) &&
 	test_must_fail git -C client cat-file -e $(git hash-object "$SERVER/two.t")
 }
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 0b62037744..022c65a7ae 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -647,7 +647,7 @@ partial_clone () {
 	git -C client fsck &&
 
 	# Ensure that unneeded blobs are not inadvertently fetched.
-	test_config -C client extensions.partialclone "not a remote" &&
+	test_config -C client odb.origin.promisorRemote "not a remote" &&
 	test_must_fail git -C client cat-file -e "$HASH1" &&
 
 	# But this blob was fetched, because clone performs an initial checkout
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index cee5565367..5ddd1e011c 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -40,7 +40,7 @@ test_expect_success 'do partial clone 1' '
 		| sort >observed.oids &&
 	test_cmp expect_1.oids observed.oids &&
 	test "$(git -C pc1 config --local core.repositoryformatversion)" = "1" &&
-	test "$(git -C pc1 config --local extensions.partialclone)" = "origin" &&
+	test "$(git -C pc1 config --local odb.origin.promisorRemote)" = "origin" &&
 	test "$(git -C pc1 config --local core.partialclonefilter)" = "blob:none"
 '
 
diff --git a/unpack-trees.c b/unpack-trees.c
index 3a85a02a77..e6ac3e6d10 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -17,6 +17,7 @@
 #include "submodule-config.h"
 #include "fsmonitor.h"
 #include "fetch-object.h"
+#include "remote-odb.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -382,7 +383,7 @@ static int check_updates(struct unpack_trees_options *o)
 		load_gitmodules_file(index, &state);
 
 	enable_delayed_checkout(&state);
-	if (repository_format_partial_clone && o->update && !o->dry_run) {
+	if (has_remote_odb() && o->update && !o->dry_run) {
 		/*
 		 * Prefetch the objects that are to be checked out in the loop
 		 * below.
@@ -399,8 +400,7 @@ static int check_updates(struct unpack_trees_options *o)
 			}
 		}
 		if (to_fetch.nr)
-			fetch_objects(repository_format_partial_clone,
-				      &to_fetch);
+			remote_odb_get_many_direct(&to_fetch);
 		fetch_if_missing = fetch_if_missing_store;
 		oid_array_clear(&to_fetch);
 	}

remote-odb.c, remote-odb.h

diff --git a/remote-odb.c b/remote-odb.c
index cc7059b23a..2b93d13abd 100644
--- a/remote-odb.c
+++ b/remote-odb.c
@@ -39,17 +39,27 @@ static int remote_odb_config(const char *var, const char *value, void *data)
 	return 0;
 }
 
-static void remote_odb_init(void)
+static void remote_odb_do_init(int force)
 {
 	static int initialized;
 
-	if (initialized)
+	if (!force && initialized)
 		return;
 	initialized = 1;
 
 	git_config(remote_odb_config, NULL);
 }
 
+static inline void remote_odb_init(void)
+{
+	remote_odb_do_init(0);
+}
+
+inline void remote_odb_reinit(void)
+{
+	remote_odb_do_init(1);
+}
+
 struct odb_helper *find_odb_helper(const char *remote)
 {
 	struct odb_helper *o;
diff --git a/remote-odb.h b/remote-odb.h
index e10a8bf855..79803782af 100644
--- a/remote-odb.h
+++ b/remote-odb.h
@@ -1,6 +1,7 @@
 #ifndef REMOTE_ODB_H
 #define REMOTE_ODB_H
 
+extern void remote_odb_reinit(void);
 extern struct odb_helper *find_odb_helper(const char *remote);
 extern int has_remote_odb(void);
 extern int remote_odb_get_direct(const unsigned char *sha1);

odb-helper.c, odb-helper.h, remote-odb.c, remote-odb.h

diff --git a/odb-helper.c b/odb-helper.c
index b4d403ffa9..99b5a345e8 100644
--- a/odb-helper.c
+++ b/odb-helper.c
@@ -4,6 +4,7 @@
 #include "odb-helper.h"
 #include "run-command.h"
 #include "sha1-lookup.h"
+#include "fetch-object.h"
 
 struct odb_helper *odb_helper_new(const char *name, int namelen)
 {
@@ -14,3 +15,16 @@ struct odb_helper *odb_helper_new(const char *name, int namelen)
 
 	return o;
 }
+
+int odb_helper_get_direct(struct odb_helper *o,
+			  const unsigned char *sha1)
+{
+	int res;
+	uint64_t start = getnanotime();
+
+	res = fetch_object(o->remote, sha1);
+
+	trace_performance_since(start, "odb_helper_get_direct");
+
+	return res;
+}
diff --git a/odb-helper.h b/odb-helper.h
index 4b792a3896..4c52e81ce8 100644
--- a/odb-helper.h
+++ b/odb-helper.h
@@ -15,5 +15,6 @@ struct odb_helper {
 };
 
 extern struct odb_helper *odb_helper_new(const char *name, int namelen);
-
+extern int odb_helper_get_direct(struct odb_helper *o,
+				 const unsigned char *sha1);
 #endif /* ODB_HELPER_H */
diff --git a/remote-odb.c b/remote-odb.c
index 1dc165eaf6..a34537c05c 100644
--- a/remote-odb.c
+++ b/remote-odb.c
@@ -70,3 +70,20 @@ int has_remote_odb(void)
 {
 	return !!find_odb_helper(NULL);
 }
+
+int remote_odb_get_direct(const unsigned char *sha1)
+{
+	struct odb_helper *o;
+
+	trace_printf("trace: remote_odb_get_direct: %s", sha1_to_hex(sha1));
+
+	remote_odb_init();
+
+	for (o = helpers; o; o = o->next) {
+		if (odb_helper_get_direct(o, sha1) < 0)
+			continue;
+		return 0;
+	}
+
+	return -1;
+}
diff --git a/remote-odb.h b/remote-odb.h
index 4c7b13695f..c5384c922d 100644
--- a/remote-odb.h
+++ b/remote-odb.h
@@ -3,5 +3,6 @@
 
 extern struct odb_helper *find_odb_helper(const char *remote);
 extern int has_remote_odb(void);
+extern int remote_odb_get_direct(const unsigned char *sha1);
 
 #endif /* REMOTE_ODB_H */

diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index 6af4712da8..4a7a662512 100755
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -162,8 +162,30 @@ test_expect_success 'fetching of missing objects' '
 	git verify-pack --verbose "$IDX" | grep "$HASH"
 '
 
+test_expect_success 'fetching of missing objects from another odb remote' '
+	git clone "file://$(pwd)/server" server2 &&
+	test_commit -C server2 bar &&
+	git -C server2 repack -a -d --write-bitmap-index &&
+	HASH2=$(git -C server2 rev-parse bar) &&
+
+	git -C repo remote add server2 "file://$(pwd)/server2" &&
+	git -C repo config odb.magic2.promisorRemote server2 &&
+	git -C repo cat-file -p "$HASH2" &&
+
+	git -C repo fetch server2 &&
+	rm -rf repo/.git/objects/* &&
+	git -C repo cat-file -p "$HASH2" &&
+
+	# Ensure that the .promisor file is written, and check that its
+	# associated packfile contains the object
+	ls repo/.git/objects/pack/pack-*.promisor >promisorlist &&
+	test_line_count = 1 promisorlist &&
+	IDX=$(cat promisorlist | sed "s/promisor$/idx/") &&
+	git verify-pack --verbose "$IDX" | grep "$HASH2"
+'
+
 test_expect_success 'rev-list stops traversal at missing and promised commit' '
-	rm -rf repo &&
+	rm -rf repo server server2 &&
 	test_create_repo repo &&
 	test_commit -C repo foo &&
 	test_commit -C repo bar &&

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ab641bf5a9..8df0c7177e 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2504,6 +2504,11 @@ This setting can be overridden with the `GIT_NOTES_REWRITE_REF`
 environment variable, which must be a colon separated list of refs or
 globs.
 
+odb.<name>.promisorRemote::
+	The name of a promisor remote. For now promisor remotes are
+	the only kind of remote object database (odb) that is
+	supported.
+
 pack.window::
 	The size of the window used by linkgit:git-pack-objects[1] when no
 	window size is given on the command line. Defaults to 10.

fetch-object.c, fetch-object.h, sha1-file.c

diff --git a/fetch-object.c b/fetch-object.c
index 853624f811..ccc4ea7f1a 100644
--- a/fetch-object.c
+++ b/fetch-object.c
@@ -5,11 +5,12 @@
 #include "transport.h"
 #include "fetch-object.h"
 
-static void fetch_refs(const char *remote_name, struct ref *ref)
+static int fetch_refs(const char *remote_name, struct ref *ref)
 {
 	struct remote *remote;
 	struct transport *transport;
 	int original_fetch_if_missing = fetch_if_missing;
+	int res;
 
 	fetch_if_missing = 0;
 	remote = remote_get(remote_name);
@@ -19,18 +20,20 @@ static void fetch_refs(const char *remote_name, struct ref *ref)
 
 	transport_set_option(transport, TRANS_OPT_FROM_PROMISOR, "1");
 	transport_set_option(transport, TRANS_OPT_NO_DEPENDENTS, "1");
-	transport_fetch_refs(transport, ref);
+	res = transport_fetch_refs(transport, ref);
 	fetch_if_missing = original_fetch_if_missing;
+
+	return res;
 }
 
-void fetch_object(const char *remote_name, const unsigned char *sha1)
+int fetch_object(const char *remote_name, const unsigned char *sha1)
 {
 	struct ref *ref = alloc_ref(sha1_to_hex(sha1));
 	hashcpy(ref->old_oid.hash, sha1);
-	fetch_refs(remote_name, ref);
+	return fetch_refs(remote_name, ref);
 }
 
-void fetch_objects(const char *remote_name, const struct oid_array *to_fetch)
+int fetch_objects(const char *remote_name, const struct oid_array *to_fetch)
 {
 	struct ref *ref = NULL;
 	int i;
@@ -41,5 +44,5 @@ void fetch_objects(const char *remote_name, const struct oid_array *to_fetch)
 		new_ref->next = ref;
 		ref = new_ref;
 	}
-	fetch_refs(remote_name, ref);
+	return fetch_refs(remote_name, ref);
 }
diff --git a/fetch-object.h b/fetch-object.h
index 4b269d07ed..12e1f9ee70 100644
--- a/fetch-object.h
+++ b/fetch-object.h
@@ -3,9 +3,9 @@
 
 #include "sha1-array.h"
 
-extern void fetch_object(const char *remote_name, const unsigned char *sha1);
+extern int fetch_object(const char *remote_name, const unsigned char *sha1);
 
-extern void fetch_objects(const char *remote_name,
-			  const struct oid_array *to_fetch);
+extern int fetch_objects(const char *remote_name,
+			 const struct oid_array *to_fetch);
 
 #endif
diff --git a/sha1-file.c b/sha1-file.c
index 695e5c6276..374a56d0e1 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -1312,8 +1312,8 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 		if (fetch_if_missing && repository_format_partial_clone &&
 		    !already_retried && r == the_repository) {
 			/*
-			 * TODO Investigate having fetch_object() return
-			 * TODO error/success and stopping the music here.
+			 * TODO Investigate checking fetch_object() return
+			 * TODO value and stopping on error here.
 			 * TODO Pass a repository struct through fetch_object,
 			 * such that arbitrary repositories work.
 			 */