Merge branch 'sb/atomic-push'

"git push" has been taught a "--atomic" option that makes push to
update more than one ref an "all-or-none" affair.

* sb/atomic-push:
  Document receive.advertiseatomic
  t5543-atomic-push.sh: add basic tests for atomic pushes
  push.c: add an --atomic argument
  send-pack.c: add --atomic command line argument
  send-pack: rename ref_update_to_be_sent to check_to_send_update
  receive-pack.c: negotiate atomic push support
  receive-pack.c: add execute_commands_atomic function
  receive-pack.c: move transaction handling in a central place
  receive-pack.c: move iterating over all commands outside execute_commands
  receive-pack.c: die instead of error in case of possible future bug
  receive-pack.c: shorten the execute_commands loop over all commands

Documentation/config.txt

@@ -2094,6 +2094,11 @@ rebase.autostash::
 	successful rebase might result in non-trivial conflicts.
 	Defaults to false.
 
+receive.advertiseatomic::
+	By default, git-receive-pack will advertise the atomic push
+	capability to its clients. If you don't want to this capability
+	to be advertised, set this variable to false.
+
 receive.autogc::
 	By default, git-receive-pack will run "git-gc --auto" after
 	receiving data from git-push and updating refs.  You can stop

Documentation/git-push.txt

@@ -9,7 +9,7 @@ git-push - Update remote refs along with associated objects
 SYNOPSIS
 --------
 [verse]
-'git push' [--all | --mirror | --tags] [--follow-tags] [-n | --dry-run] [--receive-pack=<git-receive-pack>]
+'git push' [--all | --mirror | --tags] [--follow-tags] [--atomic] [-n | --dry-run] [--receive-pack=<git-receive-pack>]
 	   [--repo=<repository>] [-f | --force] [--prune] [-v | --verbose]
 	   [-u | --set-upstream] [--signed]
 	   [--force-with-lease[=<refname>[:<expect>]]]
@@ -136,6 +136,11 @@ already exists on the remote side.
 	logged.  See linkgit:git-receive-pack[1] for the details
 	on the receiving end.
 
+--[no-]atomic::
+	Use an atomic transaction on the remote side if available.
+	Either all refs are updated, or on error, no refs are updated.
+	If the server does not support atomic pushes the push will fail.
+
 --receive-pack=<git-receive-pack>::
 --exec=<git-receive-pack>::
 	Path to the 'git-receive-pack' program on the remote

Documentation/git-send-pack.txt

@@ -9,7 +9,7 @@ git-send-pack - Push objects over Git protocol to another repository
 SYNOPSIS
 --------
 [verse]
-'git send-pack' [--all] [--dry-run] [--force] [--receive-pack=<git-receive-pack>] [--verbose] [--thin] [<host>:]<directory> [<ref>...]
+'git send-pack' [--all] [--dry-run] [--force] [--receive-pack=<git-receive-pack>] [--verbose] [--thin] [--atomic] [<host>:]<directory> [<ref>...]
 
 DESCRIPTION
 -----------
@@ -62,6 +62,11 @@ be in a separate packet, and the list must end with a flush packet.
 	Send a "thin" pack, which records objects in deltified form based
 	on objects not included in the pack to reduce network traffic.
 
+--atomic::
+	Use an atomic transaction for updating the refs. If any of the refs
+	fails to update then the entire push will fail without changing any
+	refs.
+
 <host>::
 	A remote host to house the repository.  When this
 	part is specified, 'git-receive-pack' is invoked via

Documentation/technical/protocol-capabilities.txt

@@ -18,8 +18,9 @@ was sent.  Server MUST NOT ignore capabilities that client requested
 and server advertised.  As a consequence of these rules, server MUST
 NOT advertise capabilities it does not understand.
 
-The 'report-status', 'delete-refs', 'quiet', and 'push-cert' capabilities
-are sent and recognized by the receive-pack (push to server) process.
+The 'atomic', 'report-status', 'delete-refs', 'quiet', and 'push-cert'
+capabilities are sent and recognized by the receive-pack (push to server)
+process.
 
 The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized
 by both upload-pack and receive-pack protocols.  The 'agent' capability
@@ -244,6 +245,14 @@ respond with the 'quiet' capability to suppress server-side progress
 reporting if the local progress reporting is also being suppressed
 (e.g., via `push -q`, or if stderr does not go to a tty).
 
+atomic
+------
+
+If the server sends the 'atomic' capability it is capable of accepting
+atomic pushes. If the pushing client requests this capability, the server
+will update the refs in one atomic transaction. Either all refs are
+updated or none.
+
 allow-tip-sha1-in-want
 ----------------------
 

builtin/push.c

@@ -487,6 +487,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	int flags = 0;
 	int tags = 0;
 	int rc;
+	int atomic = 0;
 	const char *repo = NULL;	/* default repository */
 	struct option options[] = {
 		OPT__VERBOSITY(&verbosity),
@@ -518,6 +519,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 		OPT_BIT(0, "follow-tags", &flags, N_("push missing but relevant tags"),
 			TRANSPORT_PUSH_FOLLOW_TAGS),
 		OPT_BIT(0, "signed", &flags, N_("GPG sign the push"), TRANSPORT_PUSH_CERT),
+		OPT_BOOL(0, "atomic", &atomic, N_("request atomic transaction on remote side")),
 		OPT_END()
 	};
 
@@ -533,6 +535,9 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	if (tags)
 		add_refspec("refs/tags/*");
 
+	if (atomic)
+		flags |= TRANSPORT_PUSH_ATOMIC;
+
 	if (argc > 0) {
 		repo = argv[0];
 		set_refspecs(argv + 1, argc - 1, repo);

builtin/receive-pack.c

@@ -38,9 +38,11 @@ static int receive_fsck_objects = -1;
 static int transfer_fsck_objects = -1;
 static int receive_unpack_limit = -1;
 static int transfer_unpack_limit = -1;
+static int advertise_atomic_push = 1;
 static int unpack_limit = 100;
 static int report_status;
 static int use_sideband;
+static int use_atomic;
 static int quiet;
 static int prefer_ofs_delta = 1;
 static int auto_update_server_info;
@@ -67,6 +69,7 @@ static const char *NONCE_SLOP = "SLOP";
 static const char *nonce_status;
 static long nonce_stamp_slop;
 static unsigned long nonce_stamp_slop_limit;
+static struct ref_transaction *transaction;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
 {
@@ -160,6 +163,11 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (strcmp(var, "receive.advertiseatomic") == 0) {
+		advertise_atomic_push = git_config_bool(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
@@ -175,6 +183,8 @@ static void show_ref(const char *path, const unsigned char *sha1)
 
 		strbuf_addstr(&cap,
 			      "report-status delete-refs side-band-64k quiet");
+		if (advertise_atomic_push)
+			strbuf_addstr(&cap, " atomic");
 		if (prefer_ofs_delta)
 			strbuf_addstr(&cap, " ofs-delta");
 		if (push_cert_nonce)
@@ -910,6 +920,7 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 	}
 
 	if (is_null_sha1(new_sha1)) {
+		struct strbuf err = STRBUF_INIT;
 		if (!parse_object(old_sha1)) {
 			old_sha1 = NULL;
 			if (ref_exists(name)) {
@@ -919,35 +930,36 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 				cmd->did_not_exist = 1;
 			}
 		}
-		if (delete_ref(namespaced_name, old_sha1, 0)) {
-			rp_error("failed to delete %s", name);
+		if (ref_transaction_delete(transaction,
+					   namespaced_name,
+					   old_sha1,
+					   0, old_sha1 != NULL,
+					   "push", &err)) {
+			rp_error("%s", err.buf);
+			strbuf_release(&err);
 			return "failed to delete";
 		}
+		strbuf_release(&err);
 		return NULL; /* good */
 	}
 	else {
 		struct strbuf err = STRBUF_INIT;
-		struct ref_transaction *transaction;
-
 		if (shallow_update && si->shallow_ref[cmd->index] &&
 		    update_shallow_ref(cmd, si))
 			return "shallow error";
 
-		transaction = ref_transaction_begin(&err);
-		if (!transaction ||
-		    ref_transaction_update(transaction, namespaced_name,
-					   new_sha1, old_sha1, 0, 1, "push",
-					   &err) ||
-		    ref_transaction_commit(transaction, &err)) {
-			ref_transaction_free(transaction);
-
+		if (ref_transaction_update(transaction,
+					   namespaced_name,
+					   new_sha1, old_sha1,
+					   0, 1, "push",
+					   &err)) {
 			rp_error("%s", err.buf);
 			strbuf_release(&err);
+
 			return "failed to update ref";
 		}
-
-		ref_transaction_free(transaction);
 		strbuf_release(&err);
+
 		return NULL; /* good */
 	}
 }
@@ -1131,11 +1143,105 @@ static void reject_updates_to_hidden(struct command *commands)
 	}
 }
 
+static int should_process_cmd(struct command *cmd)
+{
+	return !cmd->error_string && !cmd->skip_update;
+}
+
+static void warn_if_skipped_connectivity_check(struct command *commands,
+					       struct shallow_info *si)
+{
+	struct command *cmd;
+	int checked_connectivity = 1;
+
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (should_process_cmd(cmd) && si->shallow_ref[cmd->index]) {
+			error("BUG: connectivity check has not been run on ref %s",
+			      cmd->ref_name);
+			checked_connectivity = 0;
+		}
+	}
+	if (!checked_connectivity)
+		die("BUG: connectivity check skipped???");
+}
+
+static void execute_commands_non_atomic(struct command *commands,
+					struct shallow_info *si)
+{
+	struct command *cmd;
+	struct strbuf err = STRBUF_INIT;
+
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (!should_process_cmd(cmd))
+			continue;
+
+		transaction = ref_transaction_begin(&err);
+		if (!transaction) {
+			rp_error("%s", err.buf);
+			strbuf_reset(&err);
+			cmd->error_string = "transaction failed to start";
+			continue;
+		}
+
+		cmd->error_string = update(cmd, si);
+
+		if (!cmd->error_string
+		    && ref_transaction_commit(transaction, &err)) {
+			rp_error("%s", err.buf);
+			strbuf_reset(&err);
+			cmd->error_string = "failed to update ref";
+		}
+		ref_transaction_free(transaction);
+	}
+	strbuf_release(&err);
+}
+
+static void execute_commands_atomic(struct command *commands,
+					struct shallow_info *si)
+{
+	struct command *cmd;
+	struct strbuf err = STRBUF_INIT;
+	const char *reported_error = "atomic push failure";
+
+	transaction = ref_transaction_begin(&err);
+	if (!transaction) {
+		rp_error("%s", err.buf);
+		strbuf_reset(&err);
+		reported_error = "transaction failed to start";
+		goto failure;
+	}
+
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (!should_process_cmd(cmd))
+			continue;
+
+		cmd->error_string = update(cmd, si);
+
+		if (cmd->error_string)
+			goto failure;
+	}
+
+	if (ref_transaction_commit(transaction, &err)) {
+		rp_error("%s", err.buf);
+		reported_error = "atomic transaction failed";
+		goto failure;
+	}
+	goto cleanup;
+
+failure:
+	for (cmd = commands; cmd; cmd = cmd->next)
+		if (!cmd->error_string)
+			cmd->error_string = reported_error;
+
+cleanup:
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
+}
+
 static void execute_commands(struct command *commands,
 			     const char *unpacker_error,
 			     struct shallow_info *si)
 {
-	int checked_connectivity;
 	struct command *cmd;
 	unsigned char sha1[20];
 	struct iterate_data data;
@@ -1166,27 +1272,13 @@ static void execute_commands(struct command *commands,
 	free(head_name_to_free);
 	head_name = head_name_to_free = resolve_refdup("HEAD", 0, sha1, NULL);
 
-	checked_connectivity = 1;
-	for (cmd = commands; cmd; cmd = cmd->next) {
-		if (cmd->error_string)
-			continue;
-
-		if (cmd->skip_update)
-			continue;
-
-		cmd->error_string = update(cmd, si);
-		if (shallow_update && !cmd->error_string &&
-		    si->shallow_ref[cmd->index]) {
-			error("BUG: connectivity check has not been run on ref %s",
-			      cmd->ref_name);
-			checked_connectivity = 0;
-		}
-	}
+	if (use_atomic)
+		execute_commands_atomic(commands, si);
+	else
+		execute_commands_non_atomic(commands, si);
 
-	if (shallow_update && !checked_connectivity)
-		error("BUG: run 'git fsck' for safety.\n"
-		      "If there are errors, try to remove "
-		      "the reported refs above");
+	if (shallow_update)
+		warn_if_skipped_connectivity_check(commands, si);
 }
 
 static struct command **queue_command(struct command **tail,
@@ -1268,6 +1360,9 @@ static struct command *read_head_info(struct sha1_array *shallow)
 				use_sideband = LARGE_PACKET_MAX;
 			if (parse_feature_request(feature_list, "quiet"))
 				quiet = 1;
+			if (advertise_atomic_push
+			    && parse_feature_request(feature_list, "atomic"))
+				use_atomic = 1;
 		}
 
 		if (!strcmp(line, "push-cert")) {

builtin/send-pack.c

@@ -13,7 +13,7 @@
 #include "sha1-array.h"
 
 static const char send_pack_usage[] =
-"git send-pack [--all | --mirror] [--dry-run] [--force] [--receive-pack=<git-receive-pack>] [--verbose] [--thin] [<host>:]<directory> [<ref>...]\n"
+"git send-pack [--all | --mirror] [--dry-run] [--force] [--receive-pack=<git-receive-pack>] [--verbose] [--thin] [--atomic] [<host>:]<directory> [<ref>...]\n"
 "  --all and explicit <ref> specification are mutually exclusive.";
 
 static struct send_pack_args args;
@@ -170,6 +170,10 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 				args.use_thin_pack = 1;
 				continue;
 			}
+			if (!strcmp(arg, "--atomic")) {
+				args.atomic = 1;
+				continue;
+			}
 			if (!strcmp(arg, "--stateless-rpc")) {
 				args.stateless_rpc = 1;
 				continue;

remote.h

@@ -115,7 +115,8 @@ struct ref {
 		REF_STATUS_REJECT_SHALLOW,
 		REF_STATUS_UPTODATE,
 		REF_STATUS_REMOTE_REJECT,
-		REF_STATUS_EXPECTING_REPORT
+		REF_STATUS_EXPECTING_REPORT,
+		REF_STATUS_ATOMIC_PUSH_FAILED
 	} status;
 	char *remote_status;
 	struct ref *peer_ref; /* when renaming */

send-pack.c

@@ -193,10 +193,13 @@ static void advertise_shallow_grafts_buf(struct strbuf *sb)
 	for_each_commit_graft(advertise_shallow_grafts_cb, sb);
 }
 
-static int ref_update_to_be_sent(const struct ref *ref, const struct send_pack_args *args)
+#define CHECK_REF_NO_PUSH -1
+#define CHECK_REF_STATUS_REJECTED -2
+#define CHECK_REF_UPTODATE -3
+static int check_to_send_update(const struct ref *ref, const struct send_pack_args *args)
 {
 	if (!ref->peer_ref && !args->send_mirror)
-		return 0;
+		return CHECK_REF_NO_PUSH;
 
 	/* Check for statuses set by set_ref_status_for_push() */
 	switch (ref->status) {
@@ -206,10 +209,11 @@ static int ref_update_to_be_sent(const struct ref *ref, const struct send_pack_a
 	case REF_STATUS_REJECT_NEEDS_FORCE:
 	case REF_STATUS_REJECT_STALE:
 	case REF_STATUS_REJECT_NODELETE:
+		return CHECK_REF_STATUS_REJECTED;
 	case REF_STATUS_UPTODATE:
-		return 0;
+		return CHECK_REF_UPTODATE;
 	default:
-		return 1;
+		return 0;
 	}
 }
 
@@ -253,7 +257,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	strbuf_addstr(&cert, "\n");
 
 	for (ref = remote_refs; ref; ref = ref->next) {
-		if (!ref_update_to_be_sent(ref, args))
+		if (check_to_send_update(ref, args) < 0)
 			continue;
 		update_seen = 1;
 		strbuf_addf(&cert, "%s %s %s\n",
@@ -281,6 +285,29 @@ static int generate_push_cert(struct strbuf *req_buf,
 	return update_seen;
 }
 
+
+static int atomic_push_failure(struct send_pack_args *args,
+			       struct ref *remote_refs,
+			       struct ref *failing_ref)
+{
+	struct ref *ref;
+	/* Mark other refs as failed */
+	for (ref = remote_refs; ref; ref = ref->next) {
+		if (!ref->peer_ref && !args->send_mirror)
+			continue;
+
+		switch (ref->status) {
+		case REF_STATUS_EXPECTING_REPORT:
+			ref->status = REF_STATUS_ATOMIC_PUSH_FAILED;
+			continue;
+		default:
+			break; /* do nothing */
+		}
+	}
+	return error("atomic push failed for ref %s. status: %d\n",
+		     failing_ref->name, failing_ref->status);
+}
+
 int send_pack(struct send_pack_args *args,
 	      int fd[], struct child_process *conn,
 	      struct ref *remote_refs,
@@ -297,6 +324,8 @@ int send_pack(struct send_pack_args *args,
 	int use_sideband = 0;
 	int quiet_supported = 0;
 	int agent_supported = 0;
+	int use_atomic = 0;
+	int atomic_supported = 0;
 	unsigned cmds_sent = 0;
 	int ret;
 	struct async demux;
@@ -317,6 +346,8 @@ int send_pack(struct send_pack_args *args,
 		agent_supported = 1;
 	if (server_supports("no-thin"))
 		args->use_thin_pack = 0;
+	if (server_supports("atomic"))
+		atomic_supported = 1;
 	if (args->push_cert) {
 		int len;
 
@@ -331,6 +362,10 @@ int send_pack(struct send_pack_args *args,
 			"Perhaps you should specify a branch such as 'master'.\n");
 		return 0;
 	}
+	if (args->atomic && !atomic_supported)
+		die(_("server does not support --atomic push"));
+
+	use_atomic = atomic_supported && args->atomic;
 
 	if (status_report)
 		strbuf_addstr(&cap_buf, " report-status");
@@ -338,6 +373,8 @@ int send_pack(struct send_pack_args *args,
 		strbuf_addstr(&cap_buf, " side-band-64k");
 	if (quiet_supported && (args->quiet || !args->progress))
 		strbuf_addstr(&cap_buf, " quiet");
+	if (use_atomic)
+		strbuf_addstr(&cap_buf, " atomic");
 	if (agent_supported)
 		strbuf_addf(&cap_buf, " agent=%s", git_user_agent_sanitized());
 
@@ -362,9 +399,21 @@ int send_pack(struct send_pack_args *args,
 	 * the pack data.
 	 */
 	for (ref = remote_refs; ref; ref = ref->next) {
-		if (!ref_update_to_be_sent(ref, args))
+		switch (check_to_send_update(ref, args)) {
+		case 0: /* no error */
+			break;
+		case CHECK_REF_STATUS_REJECTED:
+			/*
+			 * When we know the server would reject a ref update if
+			 * we were to send it and we're trying to send the refs
+			 * atomically, abort the whole operation.
+			 */
+			if (use_atomic)
+				return atomic_push_failure(args, remote_refs, ref);
+			/* Fallthrough for non atomic case. */
+		default:
 			continue;
-
+		}
 		if (!ref->deletion)
 			need_pack_data = 1;
 
@@ -383,7 +432,7 @@ int send_pack(struct send_pack_args *args,
 		if (args->dry_run || args->push_cert)
 			continue;
 
-		if (!ref_update_to_be_sent(ref, args))
+		if (check_to_send_update(ref, args) < 0)
 			continue;
 
 		old_hex = sha1_to_hex(ref->old_sha1);

send-pack.h

@@ -13,7 +13,8 @@ struct send_pack_args {
 		use_ofs_delta:1,
 		dry_run:1,
 		push_cert:1,
-		stateless_rpc:1;
+		stateless_rpc:1,
+		atomic:1;
 };
 
 int send_pack(struct send_pack_args *args,

t/t5543-atomic-push.sh

+#!/bin/sh
+
+test_description='pushing to a repository using the atomic push option'
+
+. ./test-lib.sh
+
+mk_repo_pair () {
+	rm -rf workbench upstream &&
+	test_create_repo upstream &&
+	test_create_repo workbench &&
+	(
+		cd upstream &&
+		git config receive.denyCurrentBranch warn
+	) &&
+	(
+		cd workbench &&
+		git remote add up ../upstream
+	)
+}
+
+# Compare the ref ($1) in upstream with a ref value from workbench ($2)
+# i.e. test_refs second HEAD@{2}
+test_refs () {
+	test $# = 2 &&
+	git -C upstream rev-parse --verify "$1" >expect &&
+	git -C workbench rev-parse --verify "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'atomic push works for a single branch' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git push --mirror up &&
+		test_commit two &&
+		git push --atomic up master
+	) &&
+	test_refs master master
+'
+
+test_expect_success 'atomic push works for two branches' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git branch second &&
+		git push --mirror up &&
+		test_commit two &&
+		git checkout second &&
+		test_commit three &&
+		git push --atomic up master second
+	) &&
+	test_refs master master &&
+	test_refs second second
+'
+
+test_expect_success 'atomic push works in combination with --mirror' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git checkout -b second &&
+		test_commit two &&
+		git push --atomic --mirror up
+	) &&
+	test_refs master master &&
+	test_refs second second
+'
+
+test_expect_success 'atomic push works in combination with --force' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git branch second master &&
+		test_commit two_a &&
+		git checkout second &&
+		test_commit two_b &&
+		test_commit three_b &&
+		test_commit four &&
+		git push --mirror up &&
+		# The actual test is below
+		git checkout master &&
+		test_commit three_a &&
+		git checkout second &&
+		git reset --hard HEAD^ &&
+		git push --force --atomic up master second
+	) &&
+	test_refs master master &&
+	test_refs second second
+'
+
+# set up two branches where master can be pushed but second can not
+# (non-fast-forward). Since second can not be pushed the whole operation
+# will fail and leave master untouched.
+test_expect_success 'atomic push fails if one branch fails' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git checkout -b second master &&
+		test_commit two &&
+		test_commit three &&
+		test_commit four &&
+		git push --mirror up &&
+		git reset --hard HEAD~2 &&
+		test_commit five &&
+		git checkout master &&
+		test_commit six &&
+		test_must_fail git push --atomic --all up
+	) &&
+	test_refs master HEAD@{7} &&
+	test_refs second HEAD@{4}
+'
+
+test_expect_success 'atomic push fails if one tag fails remotely' '
+	# prepare the repo
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git checkout -b second master &&
+		test_commit two &&
+		git push --mirror up
+	) &&
+	# a third party modifies the server side:
+	(
+		cd upstream &&
+		git checkout second &&
+		git tag test_tag second
+	) &&
+	# see if we can now push both branches.
+	(
+		cd workbench &&
+		git checkout master &&
+		test_commit three &&
+		git checkout second &&
+		test_commit four &&
+		git tag test_tag &&
+		test_must_fail git push --tags --atomic up master second
+	) &&
+	test_refs master HEAD@{3} &&
+	test_refs second HEAD@{1}
+'
+
+test_expect_success 'atomic push obeys update hook preventing a branch to be pushed' '
+	mk_repo_pair &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git checkout -b second master &&
+		test_commit two &&
+		git push --mirror up
+	) &&
+	(
+		cd upstream &&
+		HOOKDIR="$(git rev-parse --git-dir)/hooks" &&
+		HOOK="$HOOKDIR/update" &&
+		mkdir -p "$HOOKDIR" &&
+		write_script "$HOOK" <<-\EOF
+			# only allow update to master from now on
+			test "$1" = "refs/heads/master"
+		EOF
+	) &&
+	(
+		cd workbench &&
+		git checkout master &&
+		test_commit three &&
+		git checkout second &&
+		test_commit four &&
+		test_must_fail git push --atomic up master second
+	) &&
+	test_refs master HEAD@{3} &&
+	test_refs second HEAD@{1}
+'
+
+test_expect_success 'atomic push is not advertised if configured' '
+	mk_repo_pair &&
+	(
+		cd upstream
+		git config receive.advertiseatomic 0
+	) &&
+	(
+		cd workbench &&
+		test_commit one &&
+		git push --mirror up &&
+		test_commit two &&
+		test_must_fail git push --atomic up master
+	) &&
+	test_refs master HEAD@{1}
+'
+
+test_done

transport.c

@@ -728,6 +728,10 @@ static int print_one_push_status(struct ref *ref, const char *dest, int count, i
 						 ref->deletion ? NULL : ref->peer_ref,
 						 "remote failed to report status", porcelain);
 		break;
+	case REF_STATUS_ATOMIC_PUSH_FAILED:
+		print_ref_status('!', "[rejected]", ref, ref->peer_ref,
+						 "atomic push failed", porcelain);
+		break;
 	case REF_STATUS_OK:
 		print_ok_ref_status(ref, porcelain);
 		break;
@@ -826,6 +830,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	args.dry_run = !!(flags & TRANSPORT_PUSH_DRY_RUN);
 	args.porcelain = !!(flags & TRANSPORT_PUSH_PORCELAIN);
 	args.push_cert = !!(flags & TRANSPORT_PUSH_CERT);
+	args.atomic = !!(flags & TRANSPORT_PUSH_ATOMIC);
 	args.url = transport->url;
 
 	ret = send_pack(&args, data->fd, data->conn, remote_refs,

transport.h

@@ -125,6 +125,7 @@ struct transport {
 #define TRANSPORT_PUSH_NO_HOOK 512
 #define TRANSPORT_PUSH_FOLLOW_TAGS 1024
 #define TRANSPORT_PUSH_CERT 2048
+#define TRANSPORT_PUSH_ATOMIC 4096
 
 #define TRANSPORT_SUMMARY_WIDTH (2 * DEFAULT_ABBREV + 3)
 #define TRANSPORT_SUMMARY(x) (int)(TRANSPORT_SUMMARY_WIDTH + strlen(x) - gettext_width(x)), (x)