Fix bug #13298 with failed backups by falling back on set-file-modes.

 src/fileio.c (Fset_file_selinux_context, Fset_file_acl): Return t if
 file's SELinux context or ACLs successfully set, nil otherwise.

 lisp/files.el (backup-buffer-copy, basic-save-buffer-2): If
 set-file-extended-attributes fails, fall back on set-file-modes
 instead of signaling an error.

 doc/lispref/files.texi (Changing Files): Document the return values of
 set-file-selinux-context and set-file-acl.

2 files changed, 20 insertions, 6 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index b79d174d35e..0beb4a73185 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2012-12-29  Eli Zaretskii  <eliz@gnu.org>
+
+        * files.el (backup-buffer-copy, basic-save-buffer-2): If
+        set-file-extended-attributes fails, fall back on set-file-modes
+        instead of signaling an error.  (Bug#13298)
+
 2012-12-29  Fabián Ezequiel Gallina  <fgallina@cuca>
 
         * progmodes/python.el: Support other commands triggering
diff --git a/lisp/files.el b/lisp/files.el
index f076530fbc8..fb82d0dbe1f 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4019,10 +4019,12 @@ BACKUPNAME is the backup file name, which is the old file renamed."
               nil)))
       ;; Reset the umask.
       (set-default-file-modes umask)))
-  (and modes
-       (set-file-modes to-name (logand modes #o1777)))
-  (and extended-attributes
-       (set-file-extended-attributes to-name extended-attributes)))
+  ;; If set-file-extended-attributes fails, fall back on set-file-modes.
+  (unless (and extended-attributes
+               (with-demoted-errors
+                 (set-file-extended-attributes to-name extended-attributes)))
+    (and modes
+         (set-file-modes to-name (logand modes #o1777)))))
 
 (defvar file-name-version-regexp
   "\\(?:~\\|\\.~[-[:alnum:]:#@^._]+\\(?:~[[:digit:]]+\\)?~\\)"
@@ -4737,8 +4739,14 @@ Before and after saving the buffer, this function runs
                (setq setmodes (list (file-modes buffer-file-name)
                                     (file-extended-attributes buffer-file-name)
                                     buffer-file-name))
-               (set-file-modes buffer-file-name (logior (car setmodes) 128))
-               (set-file-extended-attributes buffer-file-name (nth 1 setmodes)))))
+               ;; If set-file-extended-attributes fails, fall back on
+               ;; set-file-modes.
+               (unless
+                   (with-demoted-errors
+                     (set-file-extended-attributes buffer-file-name
+                                                   (nth 1 setmodes)))
+                 (set-file-modes buffer-file-name
+                                 (logior (car setmodes) 128))))))
         (let (success)
           (unwind-protect
               (progn