unix-sockets: use strbuf_getcwd()

Instead of using a PATH_MAX-sized buffer, which can be too small on some
file systems, use strbuf_getcwd(), which handles any path getcwd()
returns.  Also preserve the errno set by strbuf_getcwd() instead of
setting it to ENAMETOOLONG; that way a more appropriate error message
can be shown based on the actual reason for failing.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

unix-socket.c

@@ -18,12 +18,12 @@ static int chdir_len(const char *orig, int len)
 }
 
 struct unix_sockaddr_context {
-	char orig_dir[PATH_MAX];
+	char *orig_dir;
 };
 
 static void unix_sockaddr_cleanup(struct unix_sockaddr_context *ctx)
 {
-	if (!ctx->orig_dir[0])
+	if (!ctx->orig_dir)
 		return;
 	/*
 	 * If we fail, we can't just return an error, since we have
@@ -32,17 +32,19 @@ static void unix_sockaddr_cleanup(struct unix_sockaddr_context *ctx)
 	 */
 	if (chdir(ctx->orig_dir) < 0)
 		die("unable to restore original working directory");
+	free(ctx->orig_dir);
 }
 
 static int unix_sockaddr_init(struct sockaddr_un *sa, const char *path,
 			      struct unix_sockaddr_context *ctx)
 {
 	int size = strlen(path) + 1;
 
-	ctx->orig_dir[0] = '\0';
+	ctx->orig_dir = NULL;
 	if (size > sizeof(sa->sun_path)) {
 		const char *slash = find_last_dir_sep(path);
 		const char *dir;
+		struct strbuf cwd = STRBUF_INIT;
 
 		if (!slash) {
 			errno = ENAMETOOLONG;
@@ -56,11 +58,9 @@ static int unix_sockaddr_init(struct sockaddr_un *sa, const char *path,
 			errno = ENAMETOOLONG;
 			return -1;
 		}
-
-		if (!getcwd(ctx->orig_dir, sizeof(ctx->orig_dir))) {
-			errno = ENAMETOOLONG;
+		if (strbuf_getcwd(&cwd))
 			return -1;
-		}
+		ctx->orig_dir = strbuf_detach(&cwd, NULL);
 		if (chdir_len(dir, slash - dir) < 0)
 			return -1;
 	}