daemon/shell: refactor redirection of 0/1/2 from /dev/null

Both daemon.c and shell.c contain logic to open FDs 0/1/2 from
/dev/null if they are not already open.  Move the function in daemon.c
to setup.c and use it in shell.c, too.

While there, remove a 'not' that inverted the meaning of the comment.
The point is indeed to *avoid* messing up.

Signed-off-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -400,6 +400,8 @@ extern int path_inside_repo(const char *prefix, const char *path);
 extern int set_git_dir_init(const char *git_dir, const char *real_git_dir, int);
 extern int init_db(const char *template_dir, unsigned int flags);
 
+extern void sanitize_stdfds(void);
+
 #define alloc_nr(x) (((x)+16)*3/2)
 
 /*

daemon.c

@@ -1047,18 +1047,6 @@ static int service_loop(struct socketlist *socklist)
 	}
 }
 
-/* if any standard file descriptor is missing open it to /dev/null */
-static void sanitize_stdfds(void)
-{
-	int fd = open("/dev/null", O_RDWR, 0);
-	while (fd != -1 && fd < 2)
-		fd = dup(fd);
-	if (fd == -1)
-		die_errno("open /dev/null or dup failed");
-	if (fd > 2)
-		close(fd);
-}
-
 #ifdef NO_POSIX_GOODIES
 
 struct credentials;

setup.c

@@ -872,3 +872,15 @@ const char *resolve_gitdir(const char *suspect)
 		return suspect;
 	return read_gitfile(suspect);
 }
+
+/* if any standard file descriptor is missing open it to /dev/null */
+void sanitize_stdfds(void)
+{
+	int fd = open("/dev/null", O_RDWR, 0);
+	while (fd != -1 && fd < 2)
+		fd = dup(fd);
+	if (fd == -1)
+		die_errno("open /dev/null or dup failed");
+	if (fd > 2)
+		close(fd);
+}

shell.c

@@ -134,7 +134,6 @@ int main(int argc, char **argv)
 	char *prog;
 	const char **user_argv;
 	struct commands *cmd;
-	int devnull_fd;
 	int count;
 
 	git_setup_gettext();
@@ -143,15 +142,10 @@ int main(int argc, char **argv)
 
 	/*
 	 * Always open file descriptors 0/1/2 to avoid clobbering files
-	 * in die().  It also avoids not messing up when the pipes are
-	 * dup'ed onto stdin/stdout/stderr in the child processes we spawn.
+	 * in die().  It also avoids messing up when the pipes are dup'ed
+	 * onto stdin/stdout/stderr in the child processes we spawn.
 	 */
-	devnull_fd = open("/dev/null", O_RDWR);
-	while (devnull_fd >= 0 && devnull_fd <= 2)
-		devnull_fd = dup(devnull_fd);
-	if (devnull_fd == -1)
-		die_errno("opening /dev/null failed");
-	close (devnull_fd);
+	sanitize_stdfds();
 
 	/*
 	 * Special hack to pretend to be a CVS server