Merge branch 'js/run-command-updates'

* js/run-command-updates:
  api-run-command.txt: describe error behavior of run_command functions
  run-command.c: squelch a "use before assignment" warning
  receive-pack: remove unnecessary run_status report
  run_command: report failure to execute the program, but optionally don't
  run_command: encode deadly signal number in the return value
  run_command: report system call errors instead of returning error codes
  run_command: return exit code as positive value
  MinGW: simplify waitpid() emulation macros

11 files changed, 106 insertions, 125 deletions

diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt
index 2efe7a40be..b26c28133c 100644
--- a/Documentation/technical/api-run-command.txt
+++ b/Documentation/technical/api-run-command.txt
@@ -35,12 +35,32 @@ Functions
 	Convenience functions that encapsulate a sequence of
 	start_command() followed by finish_command(). The argument argv
 	specifies the program and its arguments. The argument opt is zero
-	or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`, or
-	`RUN_COMMAND_STDOUT_TO_STDERR` that correspond to the members
-	.no_stdin, .git_cmd, .stdout_to_stderr of `struct child_process`.
+	or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`,
+	`RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE`
+	that correspond to the members .no_stdin, .git_cmd,
+	.stdout_to_stderr, .silent_exec_failure of `struct child_process`.
 	The argument dir corresponds the member .dir. The argument env
 	corresponds to the member .env.
 
+The functions above do the following:
+
+. If a system call failed, errno is set and -1 is returned. A diagnostic
+  is printed.
+
+. If the program was not found, then -1 is returned and errno is set to
+  ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
+
+. Otherwise, the program is run. If it terminates regularly, its exit
+  code is returned. No diagnistic is printed, even if the exit code is
+  non-zero.
+
+. If the program terminated due to a signal, then the return value is the
+  signal number - 128, ie. it is negative and so indicates an unusual
+  condition; a diagnostic is printed. This return value can be passed to
+  exit(2), which will report the same code to the parent process that a
+  POSIX shell's $? would report for a program that died from the signal.
+
+
 `start_async`::
 
 	Run a function asynchronously. Takes a pointer to a `struct
@@ -143,6 +163,11 @@ string pointers (NULL terminated) in .env:
 To specify a new initial working directory for the sub-process,
 specify it in the .dir member.
 
+If the program cannot be found, the functions return -1 and set
+errno to ENOENT. Normally, an error message is printed, but if
+.silent_exec_failure is set to 1, no message is printed for this
+special error condition.
+
 
 * `struct async`
 
diff --git a/builtin-merge.c b/builtin-merge.c
index 82b546689c..0b12fb3155 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -594,7 +594,7 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 		discard_cache();
 		if (read_cache() < 0)
 			die("failed to read the cache");
-		return -ret;
+		return ret;
 	}
 }
 
diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index 6ec1d056e6..b771fe9b20 100644
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -123,31 +123,6 @@ static struct command *commands;
 static const char pre_receive_hook[] = "hooks/pre-receive";
 static const char post_receive_hook[] = "hooks/post-receive";
 
-static int run_status(int code, const char *cmd_name)
-{
-	switch (code) {
-	case 0:
-		return 0;
-	case -ERR_RUN_COMMAND_FORK:
-		return error("fork of %s failed", cmd_name);
-	case -ERR_RUN_COMMAND_EXEC:
-		return error("execute of %s failed", cmd_name);
-	case -ERR_RUN_COMMAND_PIPE:
-		return error("pipe failed");
-	case -ERR_RUN_COMMAND_WAITPID:
-		return error("waitpid failed");
-	case -ERR_RUN_COMMAND_WAITPID_WRONG_PID:
-		return error("waitpid is confused");
-	case -ERR_RUN_COMMAND_WAITPID_SIGNAL:
-		return error("%s died of signal", cmd_name);
-	case -ERR_RUN_COMMAND_WAITPID_NOEXIT:
-		return error("%s died strangely", cmd_name);
-	default:
-		error("%s exited with error code %d", cmd_name, -code);
-		return -code;
-	}
-}
-
 static int run_receive_hook(const char *hook_name)
 {
 	static char buf[sizeof(commands->old_sha1) * 2 + PATH_MAX + 4];
@@ -174,7 +149,7 @@ static int run_receive_hook(const char *hook_name)
 
 	code = start_command(&proc);
 	if (code)
-		return run_status(code, hook_name);
+		return code;
 	for (cmd = commands; cmd; cmd = cmd->next) {
 		if (!cmd->error_string) {
 			size_t n = snprintf(buf, sizeof(buf), "%s %s %s\n",
@@ -186,7 +161,7 @@ static int run_receive_hook(const char *hook_name)
 		}
 	}
 	close(proc.in);
-	return run_status(finish_command(&proc), hook_name);
+	return finish_command(&proc);
 }
 
 static int run_update_hook(struct command *cmd)
@@ -203,9 +178,8 @@ static int run_update_hook(struct command *cmd)
 	argv[3] = sha1_to_hex(cmd->new_sha1);
 	argv[4] = NULL;
 
-	return run_status(run_command_v_opt(argv, RUN_COMMAND_NO_STDIN |
-					RUN_COMMAND_STDOUT_TO_STDERR),
-			update_hook);
+	return run_command_v_opt(argv, RUN_COMMAND_NO_STDIN |
+					RUN_COMMAND_STDOUT_TO_STDERR);
 }
 
 static int is_ref_checked_out(const char *ref)
@@ -419,7 +393,6 @@ static void run_update_post_hook(struct command *cmd)
 	argv[argc] = NULL;
 	status = run_command_v_opt(argv, RUN_COMMAND_NO_STDIN
 			| RUN_COMMAND_STDOUT_TO_STDERR);
-	run_status(status, update_post_hook);
 }
 
 static void execute_commands(const char *unpacker_error)
@@ -537,7 +510,6 @@ static const char *unpack(void)
 		code = run_command_v_opt(unpacker, RUN_GIT_CMD);
 		if (!code)
 			return NULL;
-		run_status(code, unpacker[0]);
 		return "unpack-objects abnormal exit";
 	} else {
 		const char *keeper[7];
@@ -563,7 +535,6 @@ static const char *unpack(void)
 		ip.git_cmd = 1;
 		status = start_command(&ip);
 		if (status) {
-			run_status(status, keeper[0]);
 			return "index-pack fork failed";
 		}
 		pack_lockfile = index_pack_lockfile(ip.out);
@@ -573,7 +544,6 @@ static const char *unpack(void)
 			reprepare_packed_git();
 			return NULL;
 		}
-		run_status(status, keeper[0]);
 		return "index-pack abnormal exit";
 	}
 }
diff --git a/compat/mingw.h b/compat/mingw.h
index c1859c5480..948de66eb5 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -17,9 +17,10 @@ typedef int pid_t;
 #define S_IROTH 0
 #define S_IXOTH 0
 
-#define WIFEXITED(x) ((unsigned)(x) < 259)	/* STILL_ACTIVE */
+#define WIFEXITED(x) 1
+#define WIFSIGNALED(x) 0
 #define WEXITSTATUS(x) ((x) & 0xff)
-#define WIFSIGNALED(x) ((unsigned)(x) > 259)
+#define WTERMSIG(x) SIGTERM
 
 #define SIGHUP 1
 #define SIGQUIT 3
diff --git a/convert.c b/convert.c
index 1816e977b7..491e7141b4 100644
--- a/convert.c
+++ b/convert.c
@@ -267,7 +267,7 @@ static int filter_buffer(int fd, void *data)
 
 	status = finish_command(&child_process);
 	if (status)
-		error("external filter %s failed %d", params->cmd, -status);
+		error("external filter %s failed %d", params->cmd, status);
 	return (write_err || status);
 }
 
diff --git a/git.c b/git.c
index 807d875ae0..4588a8bac2 100644
--- a/git.c
+++ b/git.c
@@ -416,13 +416,9 @@ static void execv_dashed_external(const char **argv)
 	 * if we fail because the command is not found, it is
 	 * OK to return. Otherwise, we just pass along the status code.
 	 */
-	status = run_command_v_opt(argv, 0);
-	if (status != -ERR_RUN_COMMAND_EXEC) {
-		if (IS_RUN_COMMAND_ERR(status))
-			die("unable to run '%s'", argv[0]);
-		exit(-status);
-	}
-	errno = ENOENT; /* as if we called execvp */
+	status = run_command_v_opt(argv, RUN_SILENT_EXEC_FAILURE);
+	if (status >= 0 || errno != ENOENT)
+		exit(status);
 
 	argv[0] = tmp;
 
diff --git a/ll-merge.c b/ll-merge.c
index 0571564ddf..2d6b6d6cb1 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -192,10 +192,6 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 
 	args[2] = cmd.buf;
 	status = run_command_v_opt(args, 0);
-	if (status < -ERR_RUN_COMMAND_FORK)
-		; /* failure in run-command */
-	else
-		status = -status;
 	fd = open(temp[1], O_RDONLY);
 	if (fd < 0)
 		goto bad;
diff --git a/run-command.c b/run-command.c
index ff3d8e2d8b..f3e7abb7de 100644
--- a/run-command.c
+++ b/run-command.c
@@ -19,6 +19,7 @@ int start_command(struct child_process *cmd)
 {
 	int need_in, need_out, need_err;
 	int fdin[2], fdout[2], fderr[2];
+	int failed_errno = failed_errno;
 
 	/*
 	 * In case of errors we must keep the promise to close FDs
@@ -28,9 +29,10 @@ int start_command(struct child_process *cmd)
 	need_in = !cmd->no_stdin && cmd->in < 0;
 	if (need_in) {
 		if (pipe(fdin) < 0) {
+			failed_errno = errno;
 			if (cmd->out > 0)
 				close(cmd->out);
-			return -ERR_RUN_COMMAND_PIPE;
+			goto fail_pipe;
 		}
 		cmd->in = fdin[1];
 	}
@@ -40,11 +42,12 @@ int start_command(struct child_process *cmd)
 		&& cmd->out < 0;
 	if (need_out) {
 		if (pipe(fdout) < 0) {
+			failed_errno = errno;
 			if (need_in)
 				close_pair(fdin);
 			else if (cmd->in)
 				close(cmd->in);
-			return -ERR_RUN_COMMAND_PIPE;
+			goto fail_pipe;
 		}
 		cmd->out = fdout[0];
 	}
@@ -52,6 +55,7 @@ int start_command(struct child_process *cmd)
 	need_err = !cmd->no_stderr && cmd->err < 0;
 	if (need_err) {
 		if (pipe(fderr) < 0) {
+			failed_errno = errno;
 			if (need_in)
 				close_pair(fdin);
 			else if (cmd->in)
@@ -60,7 +64,11 @@ int start_command(struct child_process *cmd)
 				close_pair(fdout);
 			else if (cmd->out)
 				close(cmd->out);
-			return -ERR_RUN_COMMAND_PIPE;
+fail_pipe:
+			error("cannot create pipe for %s: %s",
+				cmd->argv[0], strerror(failed_errno));
+			errno = failed_errno;
+			return -1;
 		}
 		cmd->err = fderr[0];
 	}
@@ -122,6 +130,9 @@ int start_command(struct child_process *cmd)
 				strerror(errno));
 		exit(127);
 	}
+	if (cmd->pid < 0)
+		error("cannot fork() for %s: %s", cmd->argv[0],
+			strerror(failed_errno = errno));
 #else
 	int s0 = -1, s1 = -1, s2 = -1;	/* backups of stdin, stdout, stderr */
 	const char **sargv = cmd->argv;
@@ -173,6 +184,9 @@ int start_command(struct child_process *cmd)
 	}
 
 	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, env);
+	failed_errno = errno;
+	if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))
+		error("cannot spawn %s: %s", cmd->argv[0], strerror(errno));
 
 	if (cmd->env)
 		free_environ(env);
@@ -189,7 +203,6 @@ int start_command(struct child_process *cmd)
 #endif
 
 	if (cmd->pid < 0) {
-		int err = errno;
 		if (need_in)
 			close_pair(fdin);
 		else if (cmd->in)
@@ -200,9 +213,8 @@ int start_command(struct child_process *cmd)
 			close(cmd->out);
 		if (need_err)
 			close_pair(fderr);
-		return err == ENOENT ?
-			-ERR_RUN_COMMAND_EXEC :
-			-ERR_RUN_COMMAND_FORK;
+		errno = failed_errno;
+		return -1;
 	}
 
 	if (need_in)
@@ -221,40 +233,51 @@ int start_command(struct child_process *cmd)
 	return 0;
 }
 
-static int wait_or_whine(pid_t pid)
+static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
 {
-	for (;;) {
-		int status, code;
-		pid_t waiting = waitpid(pid, &status, 0);
-
-		if (waiting < 0) {
-			if (errno == EINTR)
-				continue;
-			error("waitpid failed (%s)", strerror(errno));
-			return -ERR_RUN_COMMAND_WAITPID;
-		}
-		if (waiting != pid)
-			return -ERR_RUN_COMMAND_WAITPID_WRONG_PID;
-		if (WIFSIGNALED(status))
-			return -ERR_RUN_COMMAND_WAITPID_SIGNAL;
-
-		if (!WIFEXITED(status))
-			return -ERR_RUN_COMMAND_WAITPID_NOEXIT;
+	int status, code = -1;
+	pid_t waiting;
+	int failed_errno = 0;
+
+	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
+		;	/* nothing */
+
+	if (waiting < 0) {
+		failed_errno = errno;
+		error("waitpid for %s failed: %s", argv0, strerror(errno));
+	} else if (waiting != pid) {
+		error("waitpid is confused (%s)", argv0);
+	} else if (WIFSIGNALED(status)) {
+		code = WTERMSIG(status);
+		error("%s died of signal %d", argv0, code);
+		/*
+		 * This return value is chosen so that code & 0xff
+		 * mimics the exit code that a POSIX shell would report for
+		 * a program that died from this signal.
+		 */
+		code -= 128;
+	} else if (WIFEXITED(status)) {
 		code = WEXITSTATUS(status);
-		switch (code) {
-		case 127:
-			return -ERR_RUN_COMMAND_EXEC;
-		case 0:
-			return 0;
-		default:
-			return -code;
+		/*
+		 * Convert special exit code when execvp failed.
+		 */
+		if (code == 127) {
+			code = -1;
+			failed_errno = ENOENT;
+			if (!silent_exec_failure)
+				error("cannot run %s: %s", argv0,
+					strerror(ENOENT));
 		}
+	} else {
+		error("waitpid is confused (%s)", argv0);
 	}
+	errno = failed_errno;
+	return code;
 }
 
 int finish_command(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid);
+	return wait_or_whine(cmd->pid, cmd->argv[0], cmd->silent_exec_failure);
 }
 
 int run_command(struct child_process *cmd)
@@ -274,6 +297,7 @@ static void prepare_run_command_v_opt(struct child_process *cmd,
 	cmd->no_stdin = opt & RUN_COMMAND_NO_STDIN ? 1 : 0;
 	cmd->git_cmd = opt & RUN_GIT_CMD ? 1 : 0;
 	cmd->stdout_to_stderr = opt & RUN_COMMAND_STDOUT_TO_STDERR ? 1 : 0;
+	cmd->silent_exec_failure = opt & RUN_SILENT_EXEC_FAILURE ? 1 : 0;
 }
 
 int run_command_v_opt(const char **argv, int opt)
@@ -338,10 +362,7 @@ int start_async(struct async *async)
 int finish_async(struct async *async)
 {
 #ifndef __MINGW32__
-	int ret = 0;
-
-	if (wait_or_whine(async->pid))
-		ret = error("waitpid (async) failed");
+	int ret = wait_or_whine(async->pid, "child process", 0);
 #else
 	DWORD ret = 0;
 	if (WaitForSingleObject(async->tid, INFINITE) != WAIT_OBJECT_0)
@@ -385,15 +406,7 @@ int run_hook(const char *index_file, const char *name, ...)
 		hook.env = env;
 	}
 
-	ret = start_command(&hook);
+	ret = run_command(&hook);
 	free(argv);
-	if (ret) {
-		warning("Could not spawn %s", argv[0]);
-		return ret;
-	}
-	ret = finish_command(&hook);
-	if (ret == -ERR_RUN_COMMAND_WAITPID_SIGNAL)
-		warning("%s exited due to uncaught signal", argv[0]);
-
 	return ret;
 }
diff --git a/run-command.h b/run-command.h
index e345502843..0c00b25ff2 100644
--- a/run-command.h
+++ b/run-command.h
@@ -1,17 +1,6 @@
 #ifndef RUN_COMMAND_H
 #define RUN_COMMAND_H
 
-enum {
-	ERR_RUN_COMMAND_FORK = 10000,
-	ERR_RUN_COMMAND_EXEC,
-	ERR_RUN_COMMAND_PIPE,
-	ERR_RUN_COMMAND_WAITPID,
-	ERR_RUN_COMMAND_WAITPID_WRONG_PID,
-	ERR_RUN_COMMAND_WAITPID_SIGNAL,
-	ERR_RUN_COMMAND_WAITPID_NOEXIT,
-};
-#define IS_RUN_COMMAND_ERR(x) (-(x) >= ERR_RUN_COMMAND_FORK)
-
 struct child_process {
 	const char **argv;
 	pid_t pid;
@@ -42,6 +31,7 @@ struct child_process {
 	unsigned no_stdout:1;
 	unsigned no_stderr:1;
 	unsigned git_cmd:1; /* if this is to be git sub-command */
+	unsigned silent_exec_failure:1;
 	unsigned stdout_to_stderr:1;
 	void (*preexec_cb)(void);
 };
@@ -55,6 +45,7 @@ extern int run_hook(const char *index_file, const char *name, ...);
 #define RUN_COMMAND_NO_STDIN 1
 #define RUN_GIT_CMD	     2	/*If this is to be git sub-command */
 #define RUN_COMMAND_STDOUT_TO_STDERR 4
+#define RUN_SILENT_EXEC_FAILURE 8
 int run_command_v_opt(const char **argv, int opt);
 
 /*
diff --git a/t/t5530-upload-pack-error.sh b/t/t5530-upload-pack-error.sh
index 757cc19ecc..a696b8791b 100755
--- a/t/t5530-upload-pack-error.sh
+++ b/t/t5530-upload-pack-error.sh
@@ -54,7 +54,10 @@ test_expect_success 'upload-pack fails due to error in rev-list' '
 	! echo "0032want $(git rev-parse HEAD)
 0034shallow $(git rev-parse HEAD^)00000009done
 0000" | git upload-pack . > /dev/null 2> output.err &&
-	grep "waitpid (async) failed" output.err
+	# pack-objects survived
+	grep "Total.*, reused" output.err &&
+	# but there was an error, which must have been in rev-list
+	grep "bad tree object" output.err
 '
 
 test_expect_success 'upload-pack fails due to error in pack-objects enumeration' '
diff --git a/transport.c b/transport.c
index de0d5874a3..8a42e76b3e 100644
--- a/transport.c
+++ b/transport.c
@@ -396,7 +396,6 @@ static int curl_transport_push(struct transport *transport, int refspec_nr, cons
 {
 	const char **argv;
 	int argc;
-	int err;
 
 	if (flags & TRANSPORT_PUSH_MIRROR)
 		return error("http transport does not support mirror mode");
@@ -416,20 +415,7 @@ static int curl_transport_push(struct transport *transport, int refspec_nr, cons
 	while (refspec_nr--)
 		argv[argc++] = *refspec++;
 	argv[argc] = NULL;
-	err = run_command_v_opt(argv, RUN_GIT_CMD);
-	switch (err) {
-	case -ERR_RUN_COMMAND_FORK:
-		error("unable to fork for %s", argv[0]);
-	case -ERR_RUN_COMMAND_EXEC:
-		error("unable to exec %s", argv[0]);
-		break;
-	case -ERR_RUN_COMMAND_WAITPID:
-	case -ERR_RUN_COMMAND_WAITPID_WRONG_PID:
-	case -ERR_RUN_COMMAND_WAITPID_SIGNAL:
-	case -ERR_RUN_COMMAND_WAITPID_NOEXIT:
-		error("%s died with strange error", argv[0]);
-	}
-	return !!err;
+	return !!run_command_v_opt(argv, RUN_GIT_CMD);
 }
 
 static struct ref *get_refs_via_curl(struct transport *transport, int for_push)