Merge branch 'cc/multi-promisor'

Teach the lazy clone machinery that there can be more than one
promisor remote and consult them in order when downloading missing
objects on demand.

* cc/multi-promisor:
  Move core_partial_clone_filter_default to promisor-remote.c
  Move repository_format_partial_clone to promisor-remote.c
  Remove fetch-object.{c,h} in favor of promisor-remote.{c,h}
  remote: add promisor and partial clone config to the doc
  partial-clone: add multiple remotes in the doc
  t0410: test fetching from many promisor remotes
  builtin/fetch: remove unique promisor remote limitation
  promisor-remote: parse remote.*.partialclonefilter
  Use promisor_remote_get_direct() and has_promisor_remote()
  promisor-remote: use repository_format_partial_clone
  promisor-remote: add promisor_remote_reinit()
  promisor-remote: implement promisor_remote_get_direct()
  Add initial support for many promisor remotes
  fetch-object: make functions return an error code
  t0410: remove pipes after git commands

Documentation/config/remote.txt

@@ -76,3 +76,11 @@ remote.<name>.pruneTags::
 +
 See also `remote.<name>.prune` and the PRUNING section of
 linkgit:git-fetch[1].
+
+remote.<name>.promisor::
+	When set to true, this remote will be used to fetch promisor
+	objects.
+
+remote.<name>.partialclonefilter::
+	The filter that will be applied when fetching from this
+	promisor remote.

Documentation/technical/partial-clone.txt

@@ -30,12 +30,20 @@ advance* during clone and fetch operations and thereby reduce download
 times and disk usage.  Missing objects can later be "demand fetched"
 if/when needed.
 
+A remote that can later provide the missing objects is called a
+promisor remote, as it promises to send the objects when
+requested. Initialy Git supported only one promisor remote, the origin
+remote from which the user cloned and that was configured in the
+"extensions.partialClone" config option. Later support for more than
+one promisor remote has been implemented.
+
 Use of partial clone requires that the user be online and the origin
-remote be available for on-demand fetching of missing objects.  This may
+remote or other promisor remotes be available for on-demand fetching
-or may not be problematic for the user.  For example, if the user can
+of missing objects.  This may or may not be problematic for the user.
-stay within the pre-selected subset of the source tree, they may not
+For example, if the user can stay within the pre-selected subset of
-encounter any missing objects.  Alternatively, the user could try to
+the source tree, they may not encounter any missing objects.
-pre-fetch various objects if they know that they are going offline.
+Alternatively, the user could try to pre-fetch various objects if they
+know that they are going offline.
 
 
 Non-Goals
@@ -100,18 +108,18 @@ or commits that reference missing trees.
 Handling Missing Objects
 ------------------------
 
-- An object may be missing due to a partial clone or fetch, or missing due
+- An object may be missing due to a partial clone or fetch, or missing
-  to repository corruption.  To differentiate these cases, the local
+  due to repository corruption.  To differentiate these cases, the
-  repository specially indicates such filtered packfiles obtained from the
+  local repository specially indicates such filtered packfiles
-  promisor remote as "promisor packfiles".
+  obtained from promisor remotes as "promisor packfiles".
 +
 These promisor packfiles consist of a "<name>.promisor" file with
 arbitrary contents (like the "<name>.keep" files), in addition to
 their "<name>.pack" and "<name>.idx" files.
 
 - The local repository considers a "promisor object" to be an object that
-  it knows (to the best of its ability) that the promisor remote has promised
+  it knows (to the best of its ability) that promisor remotes have promised
-  that it has, either because the local repository has that object in one of
+  that they have, either because the local repository has that object in one of
   its promisor packfiles, or because another promisor object refers to it.
 +
 When Git encounters a missing object, Git can see if it is a promisor object
@@ -123,12 +131,12 @@ expensive-to-modify list of missing objects.[a]
 - Since almost all Git code currently expects any referenced object to be
   present locally and because we do not want to force every command to do
   a dry-run first, a fallback mechanism is added to allow Git to attempt
-  to dynamically fetch missing objects from the promisor remote.
+  to dynamically fetch missing objects from promisor remotes.
 +
 When the normal object lookup fails to find an object, Git invokes
-fetch-object to try to get the object from the server and then retry
+promisor_remote_get_direct() to try to get the object from a promisor
-the object lookup.  This allows objects to be "faulted in" without
+remote and then retry the object lookup.  This allows objects to be
-complicated prediction algorithms.
+"faulted in" without complicated prediction algorithms.
 +
 For efficiency reasons, no check as to whether the missing object is
 actually a promisor object is performed.
@@ -157,8 +165,7 @@ and prefetch those objects in bulk.
 +
 We are not happy with this global variable and would like to remove it,
 but that requires significant refactoring of the object code to pass an
-additional flag.  We hope that concurrent efforts to add an ODB API can
+additional flag.
-encompass this.
 
 
 Fetching Missing Objects
@@ -182,21 +189,63 @@ has been updated to not use any object flags when the corresponding argument
   though they are not necessary.
 
 
+Using many promisor remotes
+---------------------------
+
+Many promisor remotes can be configured and used.
+
+This allows for example a user to have multiple geographically-close
+cache servers for fetching missing blobs while continuing to do
+filtered `git-fetch` commands from the central server.
+
+When fetching objects, promisor remotes are tried one after the other
+until all the objects have been fetched.
+
+Remotes that are considered "promisor" remotes are those specified by
+the following configuration variables:
+
+- `extensions.partialClone = <name>`
+
+- `remote.<name>.promisor = true`
+
+- `remote.<name>.partialCloneFilter = ...`
+
+Only one promisor remote can be configured using the
+`extensions.partialClone` config variable. This promisor remote will
+be the last one tried when fetching objects.
+
+We decided to make it the last one we try, because it is likely that
+someone using many promisor remotes is doing so because the other
+promisor remotes are better for some reason (maybe they are closer or
+faster for some kind of objects) than the origin, and the origin is
+likely to be the remote specified by extensions.partialClone.
+
+This justification is not very strong, but one choice had to be made,
+and anyway the long term plan should be to make the order somehow
+fully configurable.
+
+For now though the other promisor remotes will be tried in the order
+they appear in the config file.
+
 Current Limitations
 -------------------
 
-- The remote used for a partial clone (or the first partial fetch
+- It is not possible to specify the order in which the promisor
-  following a regular clone) is marked as the "promisor remote".
+  remotes are tried in other ways than the order in which they appear
+  in the config file.
 +
-We are currently limited to a single promisor remote and only that
+It is also not possible to specify an order to be used when fetching
-remote may be used for subsequent partial fetches.
+from one remote and a different order when fetching from another
-+
+remote.
-We accept this limitation because we believe initial users of this
-feature will be using it on repositories with a strong single central
-server.
 
-- Dynamic object fetching will only ask the promisor remote for missing
+- It is not possible to push only specific objects to a promisor
-  objects.  We assume that the promisor remote has a complete view of the
+  remote.
++
+It is not possible to push at the same time to multiple promisor
+remote in a specific order.
+
+- Dynamic object fetching will only ask promisor remotes for missing
+  objects.  We assume that promisor remotes have a complete view of the
   repository and can satisfy all such requests.
 
 - Repack essentially treats promisor and non-promisor packfiles as 2
@@ -218,15 +267,17 @@ server.
 Future Work
 -----------
 
-- Allow more than one promisor remote and define a strategy for fetching
+- Improve the way to specify the order in which promisor remotes are
-  missing objects from specific promisor remotes or of iterating over the
+  tried.
-  set of promisor remotes until a missing object is found.
 +
-A user might want to have multiple geographically-close cache servers
+For example this could allow to specify explicitly something like:
-for fetching missing blobs while continuing to do filtered `git-fetch`
+"When fetching from this remote, I want to use these promisor remotes
-commands from the central server, for example.
+in this order, though, when pushing or fetching to that remote, I want
+to use those promisor remotes in that order."
+
+- Allow pushing to promisor remotes.
 +
-Or the user might want to work in a triangular work flow with multiple
+The user might want to work in a triangular work flow with multiple
 promisor remotes that each have an incomplete view of the repository.
 
 - Allow repack to work on promisor packfiles (while keeping them distinct

Makefile

@@ -884,7 +884,6 @@ LIB_OBJS += ewah/ewah_io.o
 LIB_OBJS += ewah/ewah_rlw.o
 LIB_OBJS += exec-cmd.o
 LIB_OBJS += fetch-negotiator.o
-LIB_OBJS += fetch-object.o
 LIB_OBJS += fetch-pack.o
 LIB_OBJS += fsck.o
 LIB_OBJS += fsmonitor.o
@@ -948,6 +947,7 @@ LIB_OBJS += preload-index.o
 LIB_OBJS += pretty.o
 LIB_OBJS += prio-queue.o
 LIB_OBJS += progress.o
+LIB_OBJS += promisor-remote.o
 LIB_OBJS += prompt.o
 LIB_OBJS += protocol.o
 LIB_OBJS += quote.o

builtin/cat-file.c

@@ -15,6 +15,7 @@
 #include "sha1-array.h"
 #include "packfile.h"
 #include "object-store.h"
+#include "promisor-remote.h"
 
 struct batch_options {
 	int enabled;
@@ -524,8 +525,8 @@ static int batch_objects(struct batch_options *opt)
 	if (opt->all_objects) {
 		struct object_cb_data cb;
 
-		if (repository_format_partial_clone)
+		if (has_promisor_remote())
-			warning("This repository has extensions.partialClone set. Some objects may not be loaded.");
+			warning("This repository uses promisor remotes. Some objects may not be loaded.");
 
 		cb.opt = opt;
 		cb.expand = &data;

builtin/fetch.c

@@ -24,6 +24,7 @@
 #include "list-objects-filter-options.h"
 #include "commit-reach.h"
 #include "branch.h"
+#include "promisor-remote.h"
 
 #define FORCED_UPDATES_DELAY_WARNING_IN_MS (10 * 1000)
 
@@ -1559,37 +1560,27 @@ 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_promisor_remote() && !filter_options.choice)
 		return;
 
 	/*
-	 * If this is the FIRST partial-fetch request, we enable partial
+	 * If this is a partial-fetch request, we enable partial on
-	 * on this repo and remember the given filter-spec as the default
+	 * this repo if not already enabled and remember the given
-	 * for subsequent fetches to this remote.
+	 * filter-spec as the default for subsequent fetches to this
+	 * remote.
 	 */
-	if (!repository_format_partial_clone && filter_options.choice) {
+	if (filter_options.choice) {
 		partial_clone_register(remote->name, &filter_options);
 		return;
 	}
 
-	/*
-	 * 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 (filter_options.choice)
-			die(_("--filter can only be used with the remote "
-			      "configured in extensions.partialClone"));
-		return;
-	}
-
 	/*
 	 * Do a partial-fetch from the promisor remote using either the
 	 * explicitly given filter-spec or inherit the filter-spec from
 	 * 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;
 }
 
@@ -1710,7 +1701,7 @@ 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_promisor_remote())
 		die("--filter can only be used when extensions.partialClone is set");
 
 	if (all) {
@@ -1744,7 +1735,7 @@ 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_promisor_remote())
 			fetch_one_setup_partial(remote);
 		result = fetch_one(remote, argc, argv, prune_tags_ok);
 	} else {

builtin/gc.c

@@ -27,6 +27,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "promisor-remote.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -659,7 +660,7 @@ 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_promisor_remote())
 				argv_array_push(&prune,
 						"--exclude-promisor-objects");
 			if (run_command_v_opt(prune.argv, RUN_GIT_CMD))

builtin/index-pack.c

@@ -14,7 +14,7 @@
 #include "thread-utils.h"
 #include "packfile.h"
 #include "object-store.h"
-#include "fetch-object.h"
+#include "promisor-remote.h"
 
 static const char index_pack_usage[] =
 "git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
@@ -1352,7 +1352,7 @@ static void fix_unresolved_deltas(struct hashfile *f)
 		sorted_by_pos[i] = &ref_deltas[i];
 	QSORT(sorted_by_pos, nr_ref_deltas, delta_pos_compare);
 
-	if (repository_format_partial_clone) {
+	if (has_promisor_remote()) {
 		/*
 		 * Prefetch the delta bases.
 		 */
@@ -1366,8 +1366,8 @@ static void fix_unresolved_deltas(struct hashfile *f)
 			oid_array_append(&to_fetch, &d->oid);
 		}
 		if (to_fetch.nr)
-			fetch_objects(repository_format_partial_clone,
+			promisor_remote_get_direct(the_repository,
-				      to_fetch.oid, to_fetch.nr);
+						   to_fetch.oid, to_fetch.nr);
 		oid_array_clear(&to_fetch);
 	}
 

builtin/repack.c

@@ -11,6 +11,7 @@
 #include "midx.h"
 #include "packfile.h"
 #include "object-store.h"
+#include "promisor-remote.h"
 
 static int delta_base_offset = 1;
 static int pack_kept_objects = -1;
@@ -361,7 +362,7 @@ 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_promisor_remote())
 		argv_array_push(&cmd.args, "--exclude-promisor-objects");
 	if (write_bitmaps > 0)
 		argv_array_push(&cmd.args, "--write-bitmap-index");

cache-tree.c

@@ -5,6 +5,7 @@
 #include "cache-tree.h"
 #include "object-store.h"
 #include "replace-object.h"
+#include "promisor-remote.h"
 
 #ifndef DEBUG_CACHE_TREE
 #define DEBUG_CACHE_TREE 0
@@ -357,7 +358,7 @@ static int update_one(struct cache_tree *it,
 		}
 
 		ce_missing_ok = mode == S_IFGITLINK || missing_ok ||
-			(repository_format_partial_clone &&
+			(has_promisor_remote() &&
 			 ce_skip_worktree(ce));
 		if (is_null_oid(oid) ||
 		    (!ce_missing_ok && !has_object_file(oid))) {

cache.h

@@ -937,8 +937,6 @@ 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;
 extern int repository_format_worktree_config;
 
 /*

config.c

@@ -1379,11 +1379,6 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	if (!strcmp(var, "core.partialclonefilter")) {
-		return git_config_string(&core_partial_clone_filter_default,
-					 var, value);
-	}
-
 	if (!strcmp(var, "core.usereplacerefs")) {
 		read_replace_refs = git_config_bool(var, value);
 		return 0;

connected.c

@@ -5,6 +5,7 @@
 #include "connected.h"
 #include "transport.h"
 #include "packfile.h"
+#include "promisor-remote.h"
 
 /*
  * If we feed all the commits we want to verify to this command
@@ -73,7 +74,7 @@ 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_promisor_remote())
 		argv_array_push(&rev_list.args, "--exclude-promisor-objects");
 	if (!opt->is_deepening_fetch) {
 		argv_array_push(&rev_list.args, "--not");

diff.c

@@ -25,7 +25,7 @@
 #include "packfile.h"
 #include "parse-options.h"
 #include "help.h"
-#include "fetch-object.h"
+#include "promisor-remote.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
 #define FAST_WORKING_DIRECTORY 0
@@ -6520,8 +6520,7 @@ static void add_if_missing(struct repository *r,
 
 void diffcore_std(struct diff_options *options)
 {
-	if (options->repo == the_repository &&
+	if (options->repo == the_repository && has_promisor_remote()) {
-	    repository_format_partial_clone) {
 		/*
 		 * Prefetch the diff pairs that are about to be flushed.
 		 */
@@ -6538,8 +6537,8 @@ void diffcore_std(struct diff_options *options)
 			/*
 			 * NEEDSWORK: Consider deduplicating the OIDs sent.
 			 */
-			fetch_objects(repository_format_partial_clone,
+			promisor_remote_get_direct(options->repo,
-				      to_fetch.oid, to_fetch.nr);
+						   to_fetch.oid, to_fetch.nr);
 		oid_array_clear(&to_fetch);
 	}
 

environment.c

@@ -31,8 +31,6 @@ 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;
 int repository_format_worktree_config;
 const char *git_commit_encoding;
 const char *git_log_output_encoding;

fetch-object.c

@@ -1,40 +0,0 @@
-#include "cache.h"
-#include "packfile.h"
-#include "pkt-line.h"
-#include "strbuf.h"
-#include "transport.h"
-#include "fetch-object.h"
-
-static void fetch_refs(const char *remote_name, struct ref *ref)
-{
-	struct remote *remote;
-	struct transport *transport;
-	int original_fetch_if_missing = fetch_if_missing;
-
-	fetch_if_missing = 0;
-	remote = remote_get(remote_name);
-	if (!remote->url[0])
-		die(_("Remote with no URL"));
-	transport = transport_get(remote, remote->url[0]);
-
-	transport_set_option(transport, TRANS_OPT_FROM_PROMISOR, "1");
-	transport_set_option(transport, TRANS_OPT_NO_DEPENDENTS, "1");
-	transport_fetch_refs(transport, ref);
-	fetch_if_missing = original_fetch_if_missing;
-}
-
-void fetch_objects(const char *remote_name, const struct object_id *oids,
-		   int oid_nr)
-{
-	struct ref *ref = NULL;
-	int i;
-
-	for (i = 0; i < oid_nr; i++) {
-		struct ref *new_ref = alloc_ref(oid_to_hex(&oids[i]));
-		oidcpy(&new_ref->old_oid, &oids[i]);
-		new_ref->exact_oid = 1;
-		new_ref->next = ref;
-		ref = new_ref;
-	}
-	fetch_refs(remote_name, ref);
-}

fetch-object.h

@@ -1,9 +0,0 @@
-#ifndef FETCH_OBJECT_H
-#define FETCH_OBJECT_H
-
-struct object_id;
-
-void fetch_objects(const char *remote_name, const struct object_id *oids,
-		   int oid_nr);
-
-#endif

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 "promisor-remote.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_addstr(
@@ -146,41 +150,42 @@ void partial_clone_register(
 	const char *remote,
 	const struct list_objects_filter_options *filter_options)
 {
-	/*
+	char *cfg_name;
-	 * Record the name of the partial clone remote in the
+	char *filter_name;
-	 * 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"));
 
-	git_config_set("core.repositoryformatversion", "1");
+	/* Check if it is already registered */
-	git_config_set("extensions.partialclone", remote);
+	if (!promisor_remote_find(remote)) {
+		git_config_set("core.repositoryformatversion", "1");
 
-	repository_format_partial_clone = xstrdup(remote);
+		/* Add promisor config for the remote */
+		cfg_name = xstrfmt("remote.%s.promisor", remote);
+		git_config_set(cfg_name, "true");
+		free(cfg_name);
+	}
 
 	/*
 	 * Record the initial filter-spec in the config as
 	 * the default for subsequent fetches from this remote.
 	 */
-	core_partial_clone_filter_default =
+	filter_name = xstrfmt("remote.%s.partialclonefilter", remote);
-		xstrdup(filter_options->filter_spec);
+	git_config_set(filter_name, filter_options->filter_spec);
-	git_config_set("core.partialclonefilter",
+	free(filter_name);
-		       core_partial_clone_filter_default);
+
+	/* Make sure the config info are reset */
+	promisor_remote_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 promisor_remote *promisor = promisor_remote_find(remote);
+
 	/*
 	 * Parse default value, but silently ignore it if it is invalid.
 	 */
-	if (!core_partial_clone_filter_default)
+	if (promisor)
-		return;
+		gently_parse_list_objects_filter(filter_options,
-	gently_parse_list_objects_filter(filter_options,
+						 promisor->partial_clone_filter,
-					 core_partial_clone_filter_default,
+						 NULL);
-					 NULL);
 }

list-objects-filter-options.h

@@ -87,6 +87,7 @@ 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 */

packfile.c

@@ -17,6 +17,7 @@
 #include "object-store.h"
 #include "midx.h"
 #include "commit-graph.h"
+#include "promisor-remote.h"
 
 char *odb_pack_name(struct strbuf *buf,
 		    const unsigned char *sha1,
@@ -2132,7 +2133,7 @@ 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_promisor_remote()) {
 			for_each_packed_object(add_promisor_object,
 					       &promisor_objects,
 					       FOR_EACH_OBJECT_PROMISOR_ONLY);

promisor-remote.c

@@ -0,0 +1,265 @@
+#include "cache.h"
+#include "object-store.h"
+#include "promisor-remote.h"
+#include "config.h"
+#include "transport.h"
+
+static char *repository_format_partial_clone;
+static const char *core_partial_clone_filter_default;
+
+void set_repository_format_partial_clone(char *partial_clone)
+{
+	repository_format_partial_clone = xstrdup_or_null(partial_clone);
+}
+
+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);
+	if (!remote->url[0])
+		die(_("Remote with no URL"));
+	transport = transport_get(remote, remote->url[0]);
+
+	transport_set_option(transport, TRANS_OPT_FROM_PROMISOR, "1");
+	transport_set_option(transport, TRANS_OPT_NO_DEPENDENTS, "1");
+	res = transport_fetch_refs(transport, ref);
+	fetch_if_missing = original_fetch_if_missing;
+
+	return res;
+}
+
+static int fetch_objects(const char *remote_name,
+			 const struct object_id *oids,
+			 int oid_nr)
+{
+	struct ref *ref = NULL;
+	int i;
+
+	for (i = 0; i < oid_nr; i++) {
+		struct ref *new_ref = alloc_ref(oid_to_hex(&oids[i]));
+		oidcpy(&new_ref->old_oid, &oids[i]);
+		new_ref->exact_oid = 1;
+		new_ref->next = ref;
+		ref = new_ref;
+	}
+	return fetch_refs(remote_name, ref);
+}
+
+static struct promisor_remote *promisors;
+static struct promisor_remote **promisors_tail = &promisors;
+
+static struct promisor_remote *promisor_remote_new(const char *remote_name)
+{
+	struct promisor_remote *r;
+
+	if (*remote_name == '/') {
+		warning(_("promisor remote name cannot begin with '/': %s"),
+			remote_name);
+		return NULL;
+	}
+
+	FLEX_ALLOC_STR(r, name, remote_name);
+
+	*promisors_tail = r;
+	promisors_tail = &r->next;
+
+	return r;
+}
+
+static struct promisor_remote *promisor_remote_lookup(const char *remote_name,
+						      struct promisor_remote **previous)
+{
+	struct promisor_remote *r, *p;
+
+	for (p = NULL, r = promisors; r; p = r, r = r->next)
+		if (!strcmp(r->name, remote_name)) {
+			if (previous)
+				*previous = p;
+			return r;
+		}
+
+	return NULL;
+}
+
+static void promisor_remote_move_to_tail(struct promisor_remote *r,
+					 struct promisor_remote *previous)
+{
+	if (previous)
+		previous->next = r->next;
+	else
+		promisors = r->next ? r->next : r;
+	r->next = NULL;
+	*promisors_tail = r;
+	promisors_tail = &r->next;
+}
+
+static int promisor_remote_config(const char *var, const char *value, void *data)
+{
+	const char *name;
+	int namelen;
+	const char *subkey;
+
+	if (!strcmp(var, "core.partialclonefilter"))
+		return git_config_string(&core_partial_clone_filter_default,
+					 var, value);
+
+	if (parse_config_key(var, "remote", &name, &namelen, &subkey) < 0)
+		return 0;
+
+	if (!strcmp(subkey, "promisor")) {
+		char *remote_name;
+
+		if (!git_config_bool(var, value))
+			return 0;
+
+		remote_name = xmemdupz(name, namelen);
+
+		if (!promisor_remote_lookup(remote_name, NULL))
+			promisor_remote_new(remote_name);
+
+		free(remote_name);
+		return 0;
+	}
+	if (!strcmp(subkey, "partialclonefilter")) {
+		struct promisor_remote *r;
+		char *remote_name = xmemdupz(name, namelen);
+
+		r = promisor_remote_lookup(remote_name, NULL);
+		if (!r)
+			r = promisor_remote_new(remote_name);
+
+		free(remote_name);
+
+		if (!r)
+			return 0;
+
+		return git_config_string(&r->partial_clone_filter, var, value);
+	}
+
+	return 0;
+}
+
+static int initialized;
+
+static void promisor_remote_init(void)
+{
+	if (initialized)
+		return;
+	initialized = 1;
+
+	git_config(promisor_remote_config, NULL);
+
+	if (repository_format_partial_clone) {
+		struct promisor_remote *o, *previous;
+
+		o = promisor_remote_lookup(repository_format_partial_clone,
+					   &previous);
+		if (o)
+			promisor_remote_move_to_tail(o, previous);
+		else
+			promisor_remote_new(repository_format_partial_clone);
+	}
+}
+
+static void promisor_remote_clear(void)
+{
+	while (promisors) {
+		struct promisor_remote *r = promisors;
+		promisors = promisors->next;
+		free(r);
+	}
+
+	promisors_tail = &promisors;
+}
+
+void promisor_remote_reinit(void)
+{
+	initialized = 0;
+	promisor_remote_clear();
+	promisor_remote_init();
+}
+
+struct promisor_remote *promisor_remote_find(const char *remote_name)
+{
+	promisor_remote_init();
+
+	if (!remote_name)
+		return promisors;
+
+	return promisor_remote_lookup(remote_name, NULL);
+}
+
+int has_promisor_remote(void)
+{
+	return !!promisor_remote_find(NULL);
+}
+
+static int remove_fetched_oids(struct repository *repo,
+			       struct object_id **oids,
+			       int oid_nr, int to_free)
+{
+	int i, remaining_nr = 0;
+	int *remaining = xcalloc(oid_nr, sizeof(*remaining));
+	struct object_id *old_oids = *oids;
+	struct object_id *new_oids;
+
+	for (i = 0; i < oid_nr; i++)
+		if (oid_object_info_extended(repo, &old_oids[i], NULL,
+					     OBJECT_INFO_SKIP_FETCH_OBJECT)) {
+			remaining[i] = 1;
+			remaining_nr++;
+		}
+
+	if (remaining_nr) {
+		int j = 0;
+		new_oids = xcalloc(remaining_nr, sizeof(*new_oids));
+		for (i = 0; i < oid_nr; i++)
+			if (remaining[i])
+				oidcpy(&new_oids[j++], &old_oids[i]);
+		*oids = new_oids;
+		if (to_free)
+			free(old_oids);
+	}
+
+	free(remaining);
+
+	return remaining_nr;
+}
+
+int promisor_remote_get_direct(struct repository *repo,
+			       const struct object_id *oids,
+			       int oid_nr)
+{
+	struct promisor_remote *r;
+	struct object_id *remaining_oids = (struct object_id *)oids;
+	int remaining_nr = oid_nr;
+	int to_free = 0;
+	int res = -1;
+
+	promisor_remote_init();
+
+	for (r = promisors; r; r = r->next) {
+		if (fetch_objects(r->name, remaining_oids, remaining_nr) < 0) {
+			if (remaining_nr == 1)
+				continue;
+			remaining_nr = remove_fetched_oids(repo, &remaining_oids,
+							 remaining_nr, to_free);
+			if (remaining_nr) {
+				to_free = 1;
+				continue;
+			}
+		}
+		res = 0;
+		break;
+	}
+
+	if (to_free)
+		free(remaining_oids);
+
+	return res;
+}

promisor-remote.h

@@ -0,0 +1,31 @@
+#ifndef PROMISOR_REMOTE_H
+#define PROMISOR_REMOTE_H
+
+struct object_id;
+
+/*
+ * Promisor remote linked list
+ *
+ * Information in its fields come from remote.XXX config entries or
+ * from extensions.partialclone or core.partialclonefilter.
+ */
+struct promisor_remote {
+	struct promisor_remote *next;
+	const char *partial_clone_filter;
+	const char name[FLEX_ARRAY];
+};
+
+extern void promisor_remote_reinit(void);
+extern struct promisor_remote *promisor_remote_find(const char *remote_name);
+extern int has_promisor_remote(void);
+extern int promisor_remote_get_direct(struct repository *repo,
+				      const struct object_id *oids,
+				      int oid_nr);
+
+/*
+ * This should be used only once from setup.c to set the value we got
+ * from the extensions.partialclone config option.
+ */
+extern void set_repository_format_partial_clone(char *partial_clone);
+
+#endif /* PROMISOR_REMOTE_H */

setup.c

@@ -4,6 +4,7 @@
 #include "dir.h"
 #include "string-list.h"
 #include "chdir-notify.h"
+#include "promisor-remote.h"
 
 static int inside_git_dir = -1;
 static int inside_work_tree = -1;
@@ -478,7 +479,7 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 	}
 
 	repository_format_precious_objects = candidate->precious_objects;
-	repository_format_partial_clone = xstrdup_or_null(candidate->partial_clone);
+	set_repository_format_partial_clone(candidate->partial_clone);
 	repository_format_worktree_config = candidate->worktree_config;
 	string_list_clear(&candidate->unknown_extensions, 0);
 

sha1-file.c

@@ -30,8 +30,8 @@
 #include "mergesort.h"
 #include "quote.h"
 #include "packfile.h"
-#include "fetch-object.h"
 #include "object-store.h"
+#include "promisor-remote.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -1471,16 +1471,17 @@ 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_promisor_remote() &&
 		    !already_retried && r == the_repository &&
 		    !(flags & OBJECT_INFO_SKIP_FETCH_OBJECT)) {
 			/*
-			 * TODO Investigate having fetch_object() return
+			 * TODO Investigate checking promisor_remote_get_direct()
-			 * TODO error/success and stopping the music here.
+			 * TODO return value and stopping on error here.
-			 * TODO Pass a repository struct through fetch_object,
+			 * TODO Pass a repository struct through
-			 * such that arbitrary repositories work.
+			 * promisor_remote_get_direct(), such that arbitrary
+			 * repositories work.
 			 */
-			fetch_objects(repository_format_partial_clone, real, 1);
+			promisor_remote_get_direct(r, real, 1);
 			already_retried = 1;
 			continue;
 		}

t/t0410-partial-clone.sh

@@ -26,7 +26,7 @@ promise_and_delete () {
 test_expect_success 'extensions.partialclone without filter' '
 	test_create_repo server &&
 	git clone --filter="blob:none" "file://$(pwd)/server" client &&
-	git -C client config --unset core.partialclonefilter &&
+	git -C client config --unset remote.origin.partialclonefilter &&
 	git -C client fetch origin
 '
 
@@ -166,8 +166,9 @@ test_expect_success 'fetching of missing objects' '
 	# 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/") &&
+	IDX=$(sed "s/promisor$/idx/" promisorlist) &&
-	git verify-pack --verbose "$IDX" | grep "$HASH"
+	git verify-pack --verbose "$IDX" >out &&
+	grep "$HASH" out
 '
 
 test_expect_success 'fetching of missing objects works with ref-in-want enabled' '
@@ -182,8 +183,55 @@ test_expect_success 'fetching of missing objects works with ref-in-want enabled'
 	grep "git< fetch=.*ref-in-want" trace
 '
 
+test_expect_success 'fetching of missing objects from another promisor 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://$(pwd)/server2" &&
+	git -C repo config remote.server2.promisor true &&
+	git -C repo cat-file -p "$HASH2" &&
+
+	git -C repo fetch server2 &&
+	rm -rf repo/.git/objects/* &&
+	git -C repo cat-file -p "$HASH2" &&
+
+	# Ensure that the .promisor file is written, and check that its
+	# associated packfile contains the object
+	ls repo/.git/objects/pack/pack-*.promisor >promisorlist &&
+	test_line_count = 1 promisorlist &&
+	IDX=$(sed "s/promisor$/idx/" promisorlist) &&
+	git verify-pack --verbose "$IDX" >out &&
+	grep "$HASH2" out
+'
+
+test_expect_success 'fetching of missing objects configures a promisor remote' '
+	git clone "file://$(pwd)/server" server3 &&
+	test_commit -C server3 baz &&
+	git -C server3 repack -a -d --write-bitmap-index &&
+	HASH3=$(git -C server3 rev-parse baz) &&
+	git -C server3 config uploadpack.allowfilter 1 &&
+
+	rm repo/.git/objects/pack/pack-*.promisor &&
+
+	git -C repo remote add server3 "file://$(pwd)/server3" &&
+	git -C repo fetch --filter="blob:none" server3 $HASH3 &&
+
+	test_cmp_config -C repo true remote.server3.promisor &&
+
+	# Ensure that the .promisor file is written, and check that its
+	# associated packfile contains the object
+	ls repo/.git/objects/pack/pack-*.promisor >promisorlist &&
+	test_line_count = 1 promisorlist &&
+	IDX=$(sed "s/promisor$/idx/" promisorlist) &&
+	git verify-pack --verbose "$IDX" >out &&
+	grep "$HASH3" out
+'
+
 test_expect_success 'fetching of missing blobs works' '
-	rm -rf server repo &&
+	rm -rf server server2 repo &&
+	rm -rf server server3 repo &&
 	test_create_repo server &&
 	test_commit -C server foo &&
 	git -C server repack -a -d --write-bitmap-index &&
@@ -514,8 +562,9 @@ test_expect_success 'fetching of missing objects from an HTTP server' '
 	# associated packfile contains the object
 	ls repo/.git/objects/pack/pack-*.promisor >promisorlist &&
 	test_line_count = 1 promisorlist &&
-	IDX=$(cat promisorlist | sed "s/promisor$/idx/") &&
+	IDX=$(sed "s/promisor$/idx/" promisorlist) &&
-	git verify-pack --verbose "$IDX" | grep "$HASH"
+	git verify-pack --verbose "$IDX" >out &&
+	grep "$HASH" out
 '
 
 # DO NOT add non-httpd-specific tests here, because the last part of this

t/t5601-clone.sh

@@ -654,7 +654,8 @@ 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 remote.origin.promisor "false" &&
+	git -C client config --unset remote.origin.partialclonefilter &&
 	test_must_fail git -C client cat-file -e "$HASH1" &&
 
 	# But this blob was fetched, because clone performs an initial checkout

t/t5616-partial-clone.sh

@@ -42,8 +42,8 @@ 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 extensions.partialclone)" = "origin" &&
+	test "$(git -C pc1 config --local remote.origin.promisor)" = "true" &&
-	test "$(git -C pc1 config --local core.partialclonefilter)" = "blob:none"
+	test "$(git -C pc1 config --local remote.origin.partialclonefilter)" = "blob:none"
 '
 
 # checkout master to force dynamic object fetch of blobs at HEAD.

unpack-trees.c

@@ -16,7 +16,7 @@
 #include "submodule-config.h"
 #include "fsmonitor.h"
 #include "object-store.h"
-#include "fetch-object.h"
+#include "promisor-remote.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -400,7 +400,7 @@ 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_promisor_remote() && o->update && !o->dry_run) {
 		/*
 		 * Prefetch the objects that are to be checked out in the loop
 		 * below.
@@ -419,8 +419,8 @@ static int check_updates(struct unpack_trees_options *o)
 			oid_array_append(&to_fetch, &ce->oid);
 		}
 		if (to_fetch.nr)
-			fetch_objects(repository_format_partial_clone,
+			promisor_remote_get_direct(the_repository,
-				      to_fetch.oid, to_fetch.nr);
+						   to_fetch.oid, to_fetch.nr);
 		oid_array_clear(&to_fetch);
 	}
 	for (i = 0; i < index->cache_nr; i++) {