file_utils: add exists_dir_at()

src/lxc/file_utils.c

@@ -512,3 +512,15 @@ FILE *fdopen_cached(int fd, const char *mode, void **caller_freed_buffer)
 #endif
 	return f;
 }
+
+bool exists_dir_at(int dir_fd, const char *path)
+{
+	struct stat sb;
+	int ret;
+
+	ret = fstatat(dir_fd, path, &sb, 0);
+	if (ret < 0)
+		return false;
+
+	return S_ISDIR(sb.st_mode);
+}

src/lxc/file_utils.h

@@ -72,5 +72,6 @@ __hidden extern int fd_to_fd(int from, int to);
 __hidden extern int lxc_open_dirfd(const char *dir);
 __hidden extern FILE *fdopen_cached(int fd, const char *mode, void **caller_freed_buffer);
 __hidden extern FILE *fopen_cached(const char *path, const char *mode, void **caller_freed_buffer);
+__hidden extern bool exists_dir_at(int dir_fd, const char *path);
 
 #endif /* __LXC_FILE_UTILS_H */

src/lxc/utils.c

@@ -569,15 +569,7 @@ gid_t get_ns_gid(gid_t orig)
 
 bool dir_exists(const char *path)
 {
-	struct stat sb;
-	int ret;
-
-	ret = stat(path, &sb);
-	if (ret < 0)
-		/* Could be something other than eexist, just say "no". */
-		return false;
-
-	return S_ISDIR(sb.st_mode);
+	return exists_dir_at(-1, path);
 }
 
 /* Note we don't use SHA-1 here as we don't want to depend on HAVE_GNUTLS.