run-command: don't die in child when duping /dev/null

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: bmwill

run-command.c

@@ -117,18 +117,6 @@ static inline void close_pair(int fd[2])
 	close(fd[1]);
 }
 
-#ifndef GIT_WINDOWS_NATIVE
-static inline void dup_devnull(int to)
-{
-	int fd = open("/dev/null", O_RDWR);
-	if (fd < 0)
-		die_errno(_("open /dev/null failed"));
-	if (dup2(fd, to) < 0)
-		die_errno(_("dup2(%d,%d) failed"), fd, to);
-	close(fd);
-}
-#endif
-
 static char *locate_in_PATH(const char *file)
 {
 	const char *p = getenv("PATH");
@@ -444,12 +432,20 @@ int start_command(struct child_process *cmd)
 #ifndef GIT_WINDOWS_NATIVE
 {
 	int notify_pipe[2];
+	int null_fd = -1;
 	char **childenv;
 	struct argv_array argv = ARGV_ARRAY_INIT;
 
 	if (pipe(notify_pipe))
 		notify_pipe[0] = notify_pipe[1] = -1;
 
+	if (cmd->no_stdin || cmd->no_stdout || cmd->no_stderr) {
+		null_fd = open("/dev/null", O_RDWR | O_CLOEXEC);
+		if (null_fd < 0)
+			die_errno(_("open /dev/null failed"));
+		set_cloexec(null_fd);
+	}
+
 	prepare_cmd(&argv, cmd);
 	childenv = prep_childenv(cmd->env);
 
@@ -473,7 +469,7 @@ int start_command(struct child_process *cmd)
 		atexit(notify_parent);
 
 		if (cmd->no_stdin)
-			dup_devnull(0);
+			dup2(null_fd, 0);
 		else if (need_in) {
 			dup2(fdin[0], 0);
 			close_pair(fdin);
@@ -483,7 +479,7 @@ int start_command(struct child_process *cmd)
 		}
 
 		if (cmd->no_stderr)
-			dup_devnull(2);
+			dup2(null_fd, 2);
 		else if (need_err) {
 			dup2(fderr[1], 2);
 			close_pair(fderr);
@@ -493,7 +489,7 @@ int start_command(struct child_process *cmd)
 		}
 
 		if (cmd->no_stdout)
-			dup_devnull(1);
+			dup2(null_fd, 1);
 		else if (cmd->stdout_to_stderr)
 			dup2(2, 1);
 		else if (need_out) {
@@ -553,6 +549,8 @@ int start_command(struct child_process *cmd)
 	}
 	close(notify_pipe[0]);
 
+	if (null_fd >= 0)
+		close(null_fd);
 	argv_array_clear(&argv);
 	free(childenv);
 }