10 files changed, 370 insertions, 134 deletions

diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt
index 68bf4cad8b..44876fa703 100644
--- a/Documentation/technical/api-run-command.txt
+++ b/Documentation/technical/api-run-command.txt
@@ -64,8 +64,8 @@ The functions above do the following:
 `start_async`::
 
 	Run a function asynchronously. Takes a pointer to a `struct
-	async` that specifies the details and returns a pipe FD
-	from which the caller reads. See below for details.
+	async` that specifies the details and returns a set of pipe FDs
+	for communication with the function. See below for details.
 
 `finish_async`::
 
@@ -135,7 +135,7 @@ stderr as follows:
 
 	.in: The FD must be readable; it becomes child's stdin.
 	.out: The FD must be writable; it becomes child's stdout.
-	.err > 0 is not supported.
+	.err: The FD must be writable; it becomes child's stderr.
 
   The specified FD is closed by start_command(), even if it fails to
   run the sub-process!
@@ -180,17 +180,47 @@ The caller:
    struct async variable;
 2. initializes .proc and .data;
 3. calls start_async();
-4. processes the data by reading from the fd in .out;
-5. closes .out;
+4. processes communicates with proc through .in and .out;
+5. closes .in and .out;
 6. calls finish_async().
 
+The members .in, .out are used to provide a set of fd's for
+communication between the caller and the callee as follows:
+
+. Specify 0 to have no file descriptor passed.  The callee will
+  receive -1 in the corresponding argument.
+
+. Specify < 0 to have a pipe allocated; start_async() replaces
+  with the pipe FD in the following way:
+
+	.in: Returns the writable pipe end into which the caller
+	writes; the readable end of the pipe becomes the function's
+	in argument.
+
+	.out: Returns the readable pipe end from which the caller
+	reads; the writable end of the pipe becomes the function's
+	out argument.
+
+  The caller of start_async() must close the returned FDs after it
+  has completed reading from/writing from them.
+
+. Specify a file descriptor > 0 to be used by the function:
+
+	.in: The FD must be readable; it becomes the function's in.
+	.out: The FD must be writable; it becomes the function's out.
+
+  The specified FD is closed by start_async(), even if it fails to
+  run the function.
+
 The function pointer in .proc has the following signature:
 
-	int proc(int fd, void *data);
+	int proc(int in, int out, void *data);
 
-. fd specifies a writable file descriptor to which the function must
-  write the data that it produces. The function *must* close this
-  descriptor before it returns.
+. in, out specifies a set of file descriptors to which the function
+  must read/write the data that it needs/produces.  The function
+  *must* close these descriptors before it returns.  A descriptor
+  may be -1 if the caller did not configure a descriptor for that
+  direction.
 
 . data is the value that the caller has specified in the .data member
   of struct async.
@@ -205,8 +235,8 @@ because this facility is implemented by a pipe to a forked process on
 UNIX, but by a thread in the same address space on Windows:
 
 . It cannot change the program's state (global variables, environment,
-  etc.) in a way that the caller notices; in other words, .out is the
-  only communication channel to the caller.
+  etc.) in a way that the caller notices; in other words, .in and .out
+  are the only communication channels to the caller.
 
 . It must not change the program's state that the caller of the
   facility also uses.
diff --git a/builtin-fetch-pack.c b/builtin-fetch-pack.c
index 8ed4a6feaa..dbd8b7bcc8 100644
--- a/builtin-fetch-pack.c
+++ b/builtin-fetch-pack.c
@@ -586,12 +586,12 @@ static int everything_local(struct ref **refs, int nr_match, char **match)
 	return retval;
 }
 
-static int sideband_demux(int fd, void *data)
+static int sideband_demux(int in, int out, void *data)
 {
 	int *xd = data;
 
-	int ret = recv_sideband("fetch-pack", xd[0], fd);
-	close(fd);
+	int ret = recv_sideband("fetch-pack", xd[0], out);
+	close(out);
 	return ret;
 }
 
@@ -613,6 +613,7 @@ static int get_pack(int xd[2], char **pack_lockfile)
 		 */
 		demux.proc = sideband_demux;
 		demux.data = xd;
+		demux.out = -1;
 		if (start_async(&demux))
 			die("fetch-pack: unable to fork off sideband"
 			    " demultiplexer");
diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index 4320c93e70..0559fcc871 100644
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -2,6 +2,7 @@
 #include "pack.h"
 #include "refs.h"
 #include "pkt-line.h"
+#include "sideband.h"
 #include "run-command.h"
 #include "exec_cmd.h"
 #include "commit.h"
@@ -27,11 +28,12 @@ static int receive_unpack_limit = -1;
 static int transfer_unpack_limit = -1;
 static int unpack_limit = 100;
 static int report_status;
+static int use_sideband;
 static int prefer_ofs_delta = 1;
 static int auto_update_server_info;
 static int auto_gc = 1;
 static const char *head_name;
-static char *capabilities_to_send;
+static int sent_capabilities;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
 {
@@ -105,19 +107,21 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 
 static int show_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
 {
-	if (!capabilities_to_send)
+	if (sent_capabilities)
 		packet_write(1, "%s %s\n", sha1_to_hex(sha1), path);
 	else
-		packet_write(1, "%s %s%c%s\n",
-			     sha1_to_hex(sha1), path, 0, capabilities_to_send);
-	capabilities_to_send = NULL;
+		packet_write(1, "%s %s%c%s%s\n",
+			     sha1_to_hex(sha1), path, 0,
+			     " report-status delete-refs side-band-64k",
+			     prefer_ofs_delta ? " ofs-delta" : "");
+	sent_capabilities = 1;
 	return 0;
 }
 
 static void write_head_info(void)
 {
 	for_each_ref(show_ref, NULL);
-	if (capabilities_to_send)
+	if (!sent_capabilities)
 		show_ref("capabilities^{}", null_sha1, 0, NULL);
 
 }
@@ -135,11 +139,61 @@ static struct command *commands;
 static const char pre_receive_hook[] = "hooks/pre-receive";
 static const char post_receive_hook[] = "hooks/post-receive";
 
+static void rp_error(const char *err, ...) __attribute__((format (printf, 1, 2)));
+static void rp_warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
+
+static void report_message(const char *prefix, const char *err, va_list params)
+{
+	int sz = strlen(prefix);
+	char msg[4096];
+
+	strncpy(msg, prefix, sz);
+	sz += vsnprintf(msg + sz, sizeof(msg) - sz, err, params);
+	if (sz > (sizeof(msg) - 1))
+		sz = sizeof(msg) - 1;
+	msg[sz++] = '\n';
+
+	if (use_sideband)
+		send_sideband(1, 2, msg, sz, use_sideband);
+	else
+		xwrite(2, msg, sz);
+}
+
+static void rp_warning(const char *err, ...)
+{
+	va_list params;
+	va_start(params, err);
+	report_message("warning: ", err, params);
+	va_end(params);
+}
+
+static void rp_error(const char *err, ...)
+{
+	va_list params;
+	va_start(params, err);
+	report_message("error: ", err, params);
+	va_end(params);
+}
+
+static int copy_to_sideband(int in, int out, void *arg)
+{
+	char data[128];
+	while (1) {
+		ssize_t sz = xread(in, data, sizeof(data));
+		if (sz <= 0)
+			break;
+		send_sideband(1, 2, data, sz, use_sideband);
+	}
+	close(in);
+	return 0;
+}
+
 static int run_receive_hook(const char *hook_name)
 {
 	static char buf[sizeof(commands->old_sha1) * 2 + PATH_MAX + 4];
 	struct command *cmd;
 	struct child_process proc;
+	struct async muxer;
 	const char *argv[2];
 	int have_input = 0, code;
 
@@ -159,9 +213,23 @@ static int run_receive_hook(const char *hook_name)
 	proc.in = -1;
 	proc.stdout_to_stderr = 1;
 
+	if (use_sideband) {
+		memset(&muxer, 0, sizeof(muxer));
+		muxer.proc = copy_to_sideband;
+		muxer.in = -1;
+		code = start_async(&muxer);
+		if (code)
+			return code;
+		proc.err = muxer.in;
+	}
+
 	code = start_command(&proc);
-	if (code)
+	if (code) {
+		if (use_sideband)
+			finish_async(&muxer);
 		return code;
+	}
+
 	for (cmd = commands; cmd; cmd = cmd->next) {
 		if (!cmd->error_string) {
 			size_t n = snprintf(buf, sizeof(buf), "%s %s %s\n",
@@ -173,6 +241,8 @@ static int run_receive_hook(const char *hook_name)
 		}
 	}
 	close(proc.in);
+	if (use_sideband)
+		finish_async(&muxer);
 	return finish_command(&proc);
 }
 
@@ -180,6 +250,8 @@ static int run_update_hook(struct command *cmd)
 {
 	static const char update_hook[] = "hooks/update";
 	const char *argv[5];
+	struct child_process proc;
+	int code;
 
 	if (access(update_hook, X_OK) < 0)
 		return 0;
@@ -190,8 +262,18 @@ static int run_update_hook(struct command *cmd)
 	argv[3] = sha1_to_hex(cmd->new_sha1);
 	argv[4] = NULL;
 
-	return run_command_v_opt(argv, RUN_COMMAND_NO_STDIN |
-					RUN_COMMAND_STDOUT_TO_STDERR);
+	memset(&proc, 0, sizeof(proc));
+	proc.no_stdin = 1;
+	proc.stdout_to_stderr = 1;
+	proc.err = use_sideband ? -1 : 0;
+	proc.argv = argv;
+
+	code = start_command(&proc);
+	if (code)
+		return code;
+	if (use_sideband)
+		copy_to_sideband(proc.err, -1, NULL);
+	return finish_command(&proc);
 }
 
 static int is_ref_checked_out(const char *ref)
@@ -224,7 +306,7 @@ static void refuse_unconfigured_deny(void)
 {
 	int i;
 	for (i = 0; i < ARRAY_SIZE(refuse_unconfigured_deny_msg); i++)
-		error("%s", refuse_unconfigured_deny_msg[i]);
+		rp_error("%s", refuse_unconfigured_deny_msg[i]);
 }
 
 static char *refuse_unconfigured_deny_delete_current_msg[] = {
@@ -244,7 +326,7 @@ static void refuse_unconfigured_deny_delete_current(void)
 	for (i = 0;
 	     i < ARRAY_SIZE(refuse_unconfigured_deny_delete_current_msg);
 	     i++)
-		error("%s", refuse_unconfigured_deny_delete_current_msg[i]);
+		rp_error("%s", refuse_unconfigured_deny_delete_current_msg[i]);
 }
 
 static const char *update(struct command *cmd)
@@ -256,7 +338,7 @@ static const char *update(struct command *cmd)
 
 	/* only refs/... are allowed */
 	if (prefixcmp(name, "refs/") || check_ref_format(name + 5)) {
-		error("refusing to create funny ref '%s' remotely", name);
+		rp_error("refusing to create funny ref '%s' remotely", name);
 		return "funny refname";
 	}
 
@@ -265,11 +347,11 @@ static const char *update(struct command *cmd)
 		case DENY_IGNORE:
 			break;
 		case DENY_WARN:
-			warning("updating the current branch");
+			rp_warning("updating the current branch");
 			break;
 		case DENY_REFUSE:
 		case DENY_UNCONFIGURED:
-			error("refusing to update checked out branch: %s", name);
+			rp_error("refusing to update checked out branch: %s", name);
 			if (deny_current_branch == DENY_UNCONFIGURED)
 				refuse_unconfigured_deny();
 			return "branch is currently checked out";
@@ -284,7 +366,7 @@ static const char *update(struct command *cmd)
 
 	if (!is_null_sha1(old_sha1) && is_null_sha1(new_sha1)) {
 		if (deny_deletes && !prefixcmp(name, "refs/heads/")) {
-			error("denying ref deletion for %s", name);
+			rp_error("denying ref deletion for %s", name);
 			return "deletion prohibited";
 		}
 
@@ -293,13 +375,13 @@ static const char *update(struct command *cmd)
 			case DENY_IGNORE:
 				break;
 			case DENY_WARN:
-				warning("deleting the current branch");
+				rp_warning("deleting the current branch");
 				break;
 			case DENY_REFUSE:
 			case DENY_UNCONFIGURED:
 				if (deny_delete_current == DENY_UNCONFIGURED)
 					refuse_unconfigured_deny_delete_current();
-				error("refusing to delete the current branch: %s", name);
+				rp_error("refusing to delete the current branch: %s", name);
 				return "deletion of the current branch prohibited";
 			}
 		}
@@ -329,23 +411,23 @@ static const char *update(struct command *cmd)
 				break;
 		free_commit_list(bases);
 		if (!ent) {
-			error("denying non-fast-forward %s"
-			      " (you should pull first)", name);
+			rp_error("denying non-fast-forward %s"
+				 " (you should pull first)", name);
 			return "non-fast-forward";
 		}
 	}
 	if (run_update_hook(cmd)) {
-		error("hook declined to update %s", name);
+		rp_error("hook declined to update %s", name);
 		return "hook declined";
 	}
 
 	if (is_null_sha1(new_sha1)) {
 		if (!parse_object(old_sha1)) {
-			warning ("Allowing deletion of corrupt ref.");
+			rp_warning("Allowing deletion of corrupt ref.");
 			old_sha1 = NULL;
 		}
 		if (delete_ref(name, old_sha1, 0)) {
-			error("failed to delete %s", name);
+			rp_error("failed to delete %s", name);
 			return "failed to delete";
 		}
 		return NULL; /* good */
@@ -353,7 +435,7 @@ static const char *update(struct command *cmd)
 	else {
 		lock = lock_any_ref_for_update(name, old_sha1, 0);
 		if (!lock) {
-			error("failed to lock %s", name);
+			rp_error("failed to lock %s", name);
 			return "failed to lock";
 		}
 		if (write_ref_sha1(lock, new_sha1, "push")) {
@@ -368,8 +450,9 @@ static char update_post_hook[] = "hooks/post-update";
 static void run_update_post_hook(struct command *cmd)
 {
 	struct command *cmd_p;
-	int argc, status;
+	int argc;
 	const char **argv;
+	struct child_process proc;
 
 	for (argc = 0, cmd_p = cmd; cmd_p; cmd_p = cmd_p->next) {
 		if (cmd_p->error_string)
@@ -391,8 +474,18 @@ static void run_update_post_hook(struct command *cmd)
 		argc++;
 	}
 	argv[argc] = NULL;
-	status = run_command_v_opt(argv, RUN_COMMAND_NO_STDIN
-			| RUN_COMMAND_STDOUT_TO_STDERR);
+
+	memset(&proc, 0, sizeof(proc));
+	proc.no_stdin = 1;
+	proc.stdout_to_stderr = 1;
+	proc.err = use_sideband ? -1 : 0;
+	proc.argv = argv;
+
+	if (!start_command(&proc)) {
+		if (use_sideband)
+			copy_to_sideband(proc.err, -1, NULL);
+		finish_command(&proc);
+	}
 }
 
 static void execute_commands(const char *unpacker_error)
@@ -452,6 +545,8 @@ static void read_head_info(void)
 		if (reflen + 82 < len) {
 			if (strstr(refname + reflen + 1, "report-status"))
 				report_status = 1;
+			if (strstr(refname + reflen + 1, "side-band-64k"))
+				use_sideband = LARGE_PACKET_MAX;
 		}
 		cmd = xmalloc(sizeof(struct command) + len - 80);
 		hashcpy(cmd->old_sha1, old_sha1);
@@ -551,17 +646,25 @@ static const char *unpack(void)
 static void report(const char *unpack_status)
 {
 	struct command *cmd;
-	packet_write(1, "unpack %s\n",
-		     unpack_status ? unpack_status : "ok");
+	struct strbuf buf = STRBUF_INIT;
+
+	packet_buf_write(&buf, "unpack %s\n",
+			 unpack_status ? unpack_status : "ok");
 	for (cmd = commands; cmd; cmd = cmd->next) {
 		if (!cmd->error_string)
-			packet_write(1, "ok %s\n",
-				     cmd->ref_name);
+			packet_buf_write(&buf, "ok %s\n",
+					 cmd->ref_name);
 		else
-			packet_write(1, "ng %s %s\n",
-				     cmd->ref_name, cmd->error_string);
+			packet_buf_write(&buf, "ng %s %s\n",
+					 cmd->ref_name, cmd->error_string);
 	}
-	packet_flush(1);
+	packet_buf_flush(&buf);
+
+	if (use_sideband)
+		send_sideband(1, 1, buf.buf, buf.len, use_sideband);
+	else
+		safe_write(1, buf.buf, buf.len);
+	strbuf_release(&buf);
 }
 
 static int delete_only(struct command *cmd)
@@ -658,10 +761,6 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 	else if (0 <= receive_unpack_limit)
 		unpack_limit = receive_unpack_limit;
 
-	capabilities_to_send = (prefer_ofs_delta) ?
-		" report-status delete-refs ofs-delta " :
-		" report-status delete-refs ";
-
 	if (advertise_refs || !stateless_rpc) {
 		add_alternate_refs();
 		write_head_info();
@@ -695,5 +794,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 		if (auto_update_server_info)
 			update_server_info(0);
 	}
+	if (use_sideband)
+		packet_flush(1);
 	return 0;
 }
diff --git a/builtin-send-pack.c b/builtin-send-pack.c
index 76c72065de..2183a47052 100644
--- a/builtin-send-pack.c
+++ b/builtin-send-pack.c
@@ -372,6 +372,14 @@ static void print_helper_status(struct ref *ref)
 	strbuf_release(&buf);
 }
 
+static int sideband_demux(int in, int out, void *data)
+{
+	int *fd = data;
+	int ret = recv_sideband("send-pack", fd[0], out);
+	close(out);
+	return ret;
+}
+
 int send_pack(struct send_pack_args *args,
 	      int fd[], struct child_process *conn,
 	      struct ref *remote_refs,
@@ -382,18 +390,22 @@ int send_pack(struct send_pack_args *args,
 	struct strbuf req_buf = STRBUF_INIT;
 	struct ref *ref;
 	int new_refs;
-	int ask_for_status_report = 0;
 	int allow_deleting_refs = 0;
-	int expect_status_report = 0;
+	int status_report = 0;
+	int use_sideband = 0;
+	unsigned cmds_sent = 0;
 	int ret;
+	struct async demux;
 
 	/* Does the other end support the reporting? */
 	if (server_supports("report-status"))
-		ask_for_status_report = 1;
+		status_report = 1;
 	if (server_supports("delete-refs"))
 		allow_deleting_refs = 1;
 	if (server_supports("ofs-delta"))
 		args->use_ofs_delta = 1;
+	if (server_supports("side-band-64k"))
+		use_sideband = 1;
 
 	if (!remote_refs) {
 		fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
@@ -426,28 +438,30 @@ int send_pack(struct send_pack_args *args,
 		if (!ref->deletion)
 			new_refs++;
 
-		if (!args->dry_run) {
+		if (args->dry_run) {
+			ref->status = REF_STATUS_OK;
+		} else {
 			char *old_hex = sha1_to_hex(ref->old_sha1);
 			char *new_hex = sha1_to_hex(ref->new_sha1);
 
-			if (ask_for_status_report) {
-				packet_buf_write(&req_buf, "%s %s %s%c%s",
+			if (!cmds_sent && (status_report || use_sideband)) {
+				packet_buf_write(&req_buf, "%s %s %s%c%s%s",
 					old_hex, new_hex, ref->name, 0,
-					"report-status");
-				ask_for_status_report = 0;
-				expect_status_report = 1;
+					status_report ? " report-status" : "",
+					use_sideband ? " side-band-64k" : "");
 			}
 			else
 				packet_buf_write(&req_buf, "%s %s %s",
 					old_hex, new_hex, ref->name);
+			ref->status = status_report ?
+				REF_STATUS_EXPECTING_REPORT :
+				REF_STATUS_OK;
+			cmds_sent++;
 		}
-		ref->status = expect_status_report ?
-			REF_STATUS_EXPECTING_REPORT :
-			REF_STATUS_OK;
 	}
 
 	if (args->stateless_rpc) {
-		if (!args->dry_run) {
+		if (!args->dry_run && cmds_sent) {
 			packet_buf_flush(&req_buf);
 			send_sideband(out, -1, req_buf.buf, req_buf.len, LARGE_PACKET_MAX);
 		}
@@ -457,23 +471,43 @@ int send_pack(struct send_pack_args *args,
 	}
 	strbuf_release(&req_buf);
 
-	if (new_refs && !args->dry_run) {
+	if (use_sideband && cmds_sent) {
+		memset(&demux, 0, sizeof(demux));
+		demux.proc = sideband_demux;
+		demux.data = fd;
+		demux.out = -1;
+		if (start_async(&demux))
+			die("receive-pack: unable to fork off sideband demultiplexer");
+		in = demux.out;
+	}
+
+	if (new_refs && cmds_sent) {
 		if (pack_objects(out, remote_refs, extra_have, args) < 0) {
 			for (ref = remote_refs; ref; ref = ref->next)
 				ref->status = REF_STATUS_NONE;
+			if (use_sideband)
+				finish_async(&demux);
 			return -1;
 		}
 	}
-	if (args->stateless_rpc && !args->dry_run)
+	if (args->stateless_rpc && cmds_sent)
 		packet_flush(out);
 
-	if (expect_status_report)
+	if (status_report && cmds_sent)
 		ret = receive_status(in, remote_refs);
 	else
 		ret = 0;
 	if (args->stateless_rpc)
 		packet_flush(out);
 
+	if (use_sideband && cmds_sent) {
+		if (finish_async(&demux)) {
+			error("error in sideband demultiplexer");
+			ret = -1;
+		}
+		close(demux.out);
+	}
+
 	if (ret < 0)
 		return ret;
 	for (ref = remote_refs; ref; ref = ref->next) {
diff --git a/convert.c b/convert.c
index 27acce58bc..4f8fcb7bbb 100644
--- a/convert.c
+++ b/convert.c
@@ -241,7 +241,7 @@ struct filter_params {
 	const char *cmd;
 };
 
-static int filter_buffer(int fd, void *data)
+static int filter_buffer(int in, int out, void *data)
 {
 	/*
 	 * Spawn cmd and feed the buffer contents through its stdin.
@@ -255,7 +255,7 @@ static int filter_buffer(int fd, void *data)
 	child_process.argv = argv;
 	child_process.use_shell = 1;
 	child_process.in = -1;
-	child_process.out = fd;
+	child_process.out = out;
 
 	if (start_command(&child_process))
 		return error("cannot fork to run external filter %s", params->cmd);
@@ -292,6 +292,7 @@ static int apply_filter(const char *path, const char *src, size_t len,
 	memset(&async, 0, sizeof(async));
 	async.proc = filter_buffer;
 	async.data = &params;
+	async.out = -1;
 	params.src = src;
 	params.size = len;
 	params.cmd = cmd;
diff --git a/remote-curl.c b/remote-curl.c
index a904164e42..d388120851 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -184,13 +184,13 @@ static struct discovery* discover_refs(const char *service)
 	return last;
 }
 
-static int write_discovery(int fd, void *data)
+static int write_discovery(int in, int out, void *data)
 {
 	struct discovery *heads = data;
 	int err = 0;
-	if (write_in_full(fd, heads->buf, heads->len) != heads->len)
+	if (write_in_full(out, heads->buf, heads->len) != heads->len)
 		err = 1;
-	close(fd);
+	close(out);
 	return err;
 }
 
@@ -202,6 +202,7 @@ static struct ref *parse_git_refs(struct discovery *heads)
 	memset(&async, 0, sizeof(async));
 	async.proc = write_discovery;
 	async.data = heads;
+	async.out = -1;
 
 	if (start_async(&async))
 		die("cannot start thread to parse advertised refs");
diff --git a/run-command.c b/run-command.c
index 2feb493951..0cd7f02ffe 100644
--- a/run-command.c
+++ b/run-command.c
@@ -233,6 +233,9 @@ fail_pipe:
 		else if (need_err) {
 			dup2(fderr[1], 2);
 			close_pair(fderr);
+		} else if (cmd->err > 1) {
+			dup2(cmd->err, 2);
+			close(cmd->err);
 		}
 
 		if (cmd->no_stdout)
@@ -325,6 +328,8 @@ fail_pipe:
 		fherr = open("/dev/null", O_RDWR);
 	else if (need_err)
 		fherr = dup(fderr[1]);
+	else if (cmd->err > 2)
+		fherr = dup(cmd->err);
 
 	if (cmd->no_stdout)
 		fhout = open("/dev/null", O_RDWR);
@@ -394,6 +399,8 @@ fail_pipe:
 
 	if (need_err)
 		close(fderr[1]);
+	else if (cmd->err)
+		close(cmd->err);
 
 	return 0;
 }
@@ -444,17 +451,51 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
 static unsigned __stdcall run_thread(void *data)
 {
 	struct async *async = data;
-	return async->proc(async->fd_for_proc, async->data);
+	return async->proc(async->proc_in, async->proc_out, async->data);
 }
 #endif
 
 int start_async(struct async *async)
 {
-	int pipe_out[2];
+	int need_in, need_out;
+	int fdin[2], fdout[2];
+	int proc_in, proc_out;
 
-	if (pipe(pipe_out) < 0)
-		return error("cannot create pipe: %s", strerror(errno));
-	async->out = pipe_out[0];
+	need_in = async->in < 0;
+	if (need_in) {
+		if (pipe(fdin) < 0) {
+			if (async->out > 0)
+				close(async->out);
+			return error("cannot create pipe: %s", strerror(errno));
+		}
+		async->in = fdin[1];
+	}
+
+	need_out = async->out < 0;
+	if (need_out) {
+		if (pipe(fdout) < 0) {
+			if (need_in)
+				close_pair(fdin);
+			else if (async->in)
+				close(async->in);
+			return error("cannot create pipe: %s", strerror(errno));
+		}
+		async->out = fdout[0];
+	}
+
+	if (need_in)
+		proc_in = fdin[0];
+	else if (async->in)
+		proc_in = async->in;
+	else
+		proc_in = -1;
+
+	if (need_out)
+		proc_out = fdout[1];
+	else if (async->out)
+		proc_out = async->out;
+	else
+		proc_out = -1;
 
 #ifndef WIN32
 	/* Flush stdio before fork() to avoid cloning buffers */
@@ -463,24 +504,47 @@ int start_async(struct async *async)
 	async->pid = fork();
 	if (async->pid < 0) {
 		error("fork (async) failed: %s", strerror(errno));
-		close_pair(pipe_out);
-		return -1;
+		goto error;
 	}
 	if (!async->pid) {
-		close(pipe_out[0]);
-		exit(!!async->proc(pipe_out[1], async->data));
+		if (need_in)
+			close(fdin[1]);
+		if (need_out)
+			close(fdout[0]);
+		exit(!!async->proc(proc_in, proc_out, async->data));
 	}
-	close(pipe_out[1]);
+
+	if (need_in)
+		close(fdin[0]);
+	else if (async->in)
+		close(async->in);
+
+	if (need_out)
+		close(fdout[1]);
+	else if (async->out)
+		close(async->out);
 #else
-	async->fd_for_proc = pipe_out[1];
+	async->proc_in = proc_in;
+	async->proc_out = proc_out;
 	async->tid = (HANDLE) _beginthreadex(NULL, 0, run_thread, async, 0, NULL);
 	if (!async->tid) {
 		error("cannot create thread: %s", strerror(errno));
-		close_pair(pipe_out);
-		return -1;
+		goto error;
 	}
 #endif
 	return 0;
+
+error:
+	if (need_in)
+		close_pair(fdin);
+	else if (async->in)
+		close(async->in);
+
+	if (need_out)
+		close_pair(fdout);
+	else if (async->out)
+		close(async->out);
+	return -1;
 }
 
 int finish_async(struct async *async)
diff --git a/run-command.h b/run-command.h
index 967ba8cc09..94619f52d9 100644
--- a/run-command.h
+++ b/run-command.h
@@ -18,7 +18,7 @@ struct child_process {
 	 * - Specify > 0 to set a channel to a particular FD as follows:
 	 *     .in: a readable FD, becomes child's stdin
 	 *     .out: a writable FD, becomes child's stdout/stderr
-	 *     .err > 0 not supported
+	 *     .err: a writable FD, becomes child's stderr
 	 *   The specified FD is closed by start_command(), even in case
 	 *   of errors!
 	 */
@@ -66,17 +66,20 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
  */
 struct async {
 	/*
-	 * proc writes to fd and closes it;
+	 * proc reads from in; closes it before return
+	 * proc writes to out; closes it before return
 	 * returns 0 on success, non-zero on failure
 	 */
-	int (*proc)(int fd, void *data);
+	int (*proc)(int in, int out, void *data);
 	void *data;
+	int in;		/* caller writes here and closes it */
 	int out;	/* caller reads from here and closes it */
 #ifndef WIN32
 	pid_t pid;
 #else
 	HANDLE tid;
-	int fd_for_proc;
+	int proc_in;
+	int proc_out;
 #endif
 };
 
diff --git a/t/t5401-update-hooks.sh b/t/t5401-update-hooks.sh
index 325714e529..17bcb0b040 100755
--- a/t/t5401-update-hooks.sh
+++ b/t/t5401-update-hooks.sh
@@ -17,23 +17,22 @@ test_expect_success setup '
 	commit1=$(echo modify | git commit-tree $tree1 -p $commit0) &&
 	git update-ref refs/heads/master $commit0 &&
 	git update-ref refs/heads/tofail $commit1 &&
-	git clone ./. victim &&
-	GIT_DIR=victim/.git git config receive.denyCurrentBranch warn &&
-	GIT_DIR=victim/.git git update-ref refs/heads/tofail $commit1 &&
+	git clone --bare ./. victim.git &&
+	GIT_DIR=victim.git git update-ref refs/heads/tofail $commit1 &&
 	git update-ref refs/heads/master $commit1 &&
 	git update-ref refs/heads/tofail $commit0
 '
 
-cat >victim/.git/hooks/pre-receive <<'EOF'
+cat >victim.git/hooks/pre-receive <<'EOF'
 #!/bin/sh
 printf %s "$@" >>$GIT_DIR/pre-receive.args
 cat - >$GIT_DIR/pre-receive.stdin
 echo STDOUT pre-receive
 echo STDERR pre-receive >&2
 EOF
-chmod u+x victim/.git/hooks/pre-receive
+chmod u+x victim.git/hooks/pre-receive
 
-cat >victim/.git/hooks/update <<'EOF'
+cat >victim.git/hooks/update <<'EOF'
 #!/bin/sh
 echo "$@" >>$GIT_DIR/update.args
 read x; printf %s "$x" >$GIT_DIR/update.stdin
@@ -41,77 +40,77 @@ echo STDOUT update $1
 echo STDERR update $1 >&2
 test "$1" = refs/heads/master || exit
 EOF
-chmod u+x victim/.git/hooks/update
+chmod u+x victim.git/hooks/update
 
-cat >victim/.git/hooks/post-receive <<'EOF'
+cat >victim.git/hooks/post-receive <<'EOF'
 #!/bin/sh
 printf %s "$@" >>$GIT_DIR/post-receive.args
 cat - >$GIT_DIR/post-receive.stdin
 echo STDOUT post-receive
 echo STDERR post-receive >&2
 EOF
-chmod u+x victim/.git/hooks/post-receive
+chmod u+x victim.git/hooks/post-receive
 
-cat >victim/.git/hooks/post-update <<'EOF'
+cat >victim.git/hooks/post-update <<'EOF'
 #!/bin/sh
 echo "$@" >>$GIT_DIR/post-update.args
 read x; printf %s "$x" >$GIT_DIR/post-update.stdin
 echo STDOUT post-update
 echo STDERR post-update >&2
 EOF
-chmod u+x victim/.git/hooks/post-update
+chmod u+x victim.git/hooks/post-update
 
 test_expect_success push '
-	test_must_fail git send-pack --force ./victim/.git \
+	test_must_fail git send-pack --force ./victim.git \
 		master tofail >send.out 2>send.err
 '
 
 test_expect_success 'updated as expected' '
-	test $(GIT_DIR=victim/.git git rev-parse master) = $commit1 &&
-	test $(GIT_DIR=victim/.git git rev-parse tofail) = $commit1
+	test $(GIT_DIR=victim.git git rev-parse master) = $commit1 &&
+	test $(GIT_DIR=victim.git git rev-parse tofail) = $commit1
 '
 
 test_expect_success 'hooks ran' '
-	test -f victim/.git/pre-receive.args &&
-	test -f victim/.git/pre-receive.stdin &&
-	test -f victim/.git/update.args &&
-	test -f victim/.git/update.stdin &&
-	test -f victim/.git/post-receive.args &&
-	test -f victim/.git/post-receive.stdin &&
-	test -f victim/.git/post-update.args &&
-	test -f victim/.git/post-update.stdin
+	test -f victim.git/pre-receive.args &&
+	test -f victim.git/pre-receive.stdin &&
+	test -f victim.git/update.args &&
+	test -f victim.git/update.stdin &&
+	test -f victim.git/post-receive.args &&
+	test -f victim.git/post-receive.stdin &&
+	test -f victim.git/post-update.args &&
+	test -f victim.git/post-update.stdin
 '
 
 test_expect_success 'pre-receive hook input' '
 	(echo $commit0 $commit1 refs/heads/master;
 	 echo $commit1 $commit0 refs/heads/tofail
-	) | test_cmp - victim/.git/pre-receive.stdin
+	) | test_cmp - victim.git/pre-receive.stdin
 '
 
 test_expect_success 'update hook arguments' '
 	(echo refs/heads/master $commit0 $commit1;
 	 echo refs/heads/tofail $commit1 $commit0
-	) | test_cmp - victim/.git/update.args
+	) | test_cmp - victim.git/update.args
 '
 
 test_expect_success 'post-receive hook input' '
 	echo $commit0 $commit1 refs/heads/master |
-	test_cmp - victim/.git/post-receive.stdin
+	test_cmp - victim.git/post-receive.stdin
 '
 
 test_expect_success 'post-update hook arguments' '
 	echo refs/heads/master |
-	test_cmp - victim/.git/post-update.args
+	test_cmp - victim.git/post-update.args
 '
 
 test_expect_success 'all hook stdin is /dev/null' '
-	! test -s victim/.git/update.stdin &&
-	! test -s victim/.git/post-update.stdin
+	! test -s victim.git/update.stdin &&
+	! test -s victim.git/post-update.stdin
 '
 
 test_expect_success 'all *-receive hook args are empty' '
-	! test -s victim/.git/pre-receive.args &&
-	! test -s victim/.git/post-receive.args
+	! test -s victim.git/pre-receive.args &&
+	! test -s victim.git/post-receive.args
 '
 
 test_expect_success 'send-pack produced no output' '
@@ -119,20 +118,21 @@ test_expect_success 'send-pack produced no output' '
 '
 
 cat <<EOF >expect
-STDOUT pre-receive
-STDERR pre-receive
-STDOUT update refs/heads/master
-STDERR update refs/heads/master
-STDOUT update refs/heads/tofail
-STDERR update refs/heads/tofail
-STDOUT post-receive
-STDERR post-receive
-STDOUT post-update
-STDERR post-update
+remote: STDOUT pre-receive
+remote: STDERR pre-receive
+remote: STDOUT update refs/heads/master
+remote: STDERR update refs/heads/master
+remote: STDOUT update refs/heads/tofail
+remote: STDERR update refs/heads/tofail
+remote: error: hook declined to update refs/heads/tofail
+remote: STDOUT post-receive
+remote: STDERR post-receive
+remote: STDOUT post-update
+remote: STDERR post-update
 EOF
 test_expect_success 'send-pack stderr contains hook messages' '
-	grep ^STD send.err >actual &&
-	test_cmp - actual <expect
+	grep ^remote: send.err | sed "s/ *\$//" >actual &&
+	test_cmp expect actual
 '
 
 test_done
diff --git a/upload-pack.c b/upload-pack.c
index df151813f9..dc464d78b3 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -105,12 +105,12 @@ static void show_edge(struct commit *commit)
 	fprintf(pack_pipe, "-%s\n", sha1_to_hex(commit->object.sha1));
 }
 
-static int do_rev_list(int fd, void *create_full_pack)
+static int do_rev_list(int in, int out, void *create_full_pack)
 {
 	int i;
 	struct rev_info revs;
 
-	pack_pipe = xfdopen(fd, "w");
+	pack_pipe = xfdopen(out, "w");
 	init_revisions(&revs, NULL);
 	revs.tag_objects = 1;
 	revs.tree_objects = 1;
@@ -162,8 +162,9 @@ static void create_pack_file(void)
 	int arg = 0;
 
 	if (shallow_nr) {
+		memset(&rev_list, 0, sizeof(rev_list));
 		rev_list.proc = do_rev_list;
-		rev_list.data = 0;
+		rev_list.out = -1;
 		if (start_async(&rev_list))
 			die("git upload-pack: unable to fork git-rev-list");
 		argv[arg++] = "pack-objects";