Re: backup-buffer-copy loops if old backup can't be deleted

[martin rudalics]

> > I think there is no need to explicitly check whether the directory
> > is writable.  What would be the purpose of that?
>
>
> I didn't write that patch, but I guess there could be a purpose for it.
> Namely it could help deleting a file in vain. If there are Filesystems
> that let you delete a writable file even though you can't create new
> ones in a non-writable dir, then without those lines, emacs would delete
> an old backup only to find out that it can't create a new one.
>
> Most likely these would be cases where the old backup file was writable,
> so if you had some logic to write to existing files and only delete them
> if they are not writable, then the check whether the directory is
> writable should really be superfluous. Otherwise I'm not so sure.

Wouldn't it be simpler to try something like the attached patch.

*** files.el    Fri Aug 24 07:28:20 2007
--- files.el    Fri Aug 24 11:04:42 2007
***************
*** 3172,3198 ****
            (file-error nil))))))
  
  (defun backup-buffer-copy (from-name to-name modes)
!   (let ((umask (default-file-modes))
!       (dir (or (file-name-directory to-name)
!                default-directory)))
      (unwind-protect
        (progn
          ;; Create temp files with strict access rights.  It's easy to
          ;; loosen them later, whereas it's impossible to close the
          ;; time-window of loose permissions otherwise.
          (set-default-file-modes ?\700)
!         (while (condition-case ()
!                    (progn
!                      (and (file-exists-p to-name)
!                           (delete-file to-name))
!                      (copy-file from-name to-name nil t)
!                      nil)
!                  (file-already-exists t))
!           ;; The file was somehow created by someone else between
!           ;; `delete-file' and `copy-file', so let's try again.
!           ;; rms says "I think there is also a possible race
!           ;; condition for making backup files" (emacs-devel 20070821).
!           nil))
        ;; Reset the umask.
        (set-default-file-modes umask)))
    (and modes
--- 3172,3200 ----
            (file-error nil))))))
  
  (defun backup-buffer-copy (from-name to-name modes)
!   (let ((umask (default-file-modes)))
      (unwind-protect
        (progn
          ;; Create temp files with strict access rights.  It's easy to
          ;; loosen them later, whereas it's impossible to close the
          ;; time-window of loose permissions otherwise.
          (set-default-file-modes ?\700)
!         (when (condition-case nil
!                   ;; Try to overwrite old backup first.
!                   (copy-file from-name to-name t t)
!                 (file-error t))
!           (while (condition-case nil
!                      (progn
!                        (when (file-exists-p to-name)
!                          (delete-file to-name))
!                        (copy-file from-name to-name nil t)
!                        nil)
!                    (file-already-exists t))
!             ;; The file was somehow created by someone else between
!             ;; `delete-file' and `copy-file', so let's try again.
!             ;; rms says "I think there is also a possible race
!             ;; condition for making backup files" (emacs-devel 20070821).
!             nil)))
        ;; Reset the umask.
        (set-default-file-modes umask)))
    (and modes