--- Begin Message ---
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Subject: |
30.0.50; save-buffer to write-protected file without backup fails |
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Date: |
Sat, 14 Oct 2023 21:09:53 +0200 |
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User-agent: |
Mozilla Thunderbird |
X-Debbugs-Cc: Eli Zaretskii <eliz@gnu.org>
Severity: minor
Eli, sorry to disturb you with another edge-case bug, but the commit
that has introduced it was yours, I think ...
*** Issue A
In a shell execute:
echo foo > foo
chmod 0400 foo
./src/emacs -Q foo
C-x C-q
bar
C-0 C-x C-s
=> File foo is write-protected; try to save anyway?
yes RET
=> basic-save-buffer-2: Opening output file: Permission denied,
/home/jschmidt/work/emacs-master/foo
When saving *with* backup, that is, without prefix C-0, everything works
as expected: The file temporarily gets write permissions, gets written
to, and write permissions get removed again.
The root cause is related to Eli's introduction of calls to
`set-file-extended-attributes' in ccad023bc3c7. Here:
------------------------- files.el -------------------------
;; If file not writable, see if we can make it writable
;; temporarily while we write it.
;; But no need to do so if we have just backed it up
;; (setmodes is set) because that says we're superseding.
(cond ((and tempsetmodes (not setmodes))
;; Change the mode back, after writing.
(setq setmodes
(list (file-modes buffer-file-name)
(with-demoted-errors
"Error getting extended attributes: %s"
(file-extended-attributes buffer-file-name))
buffer-file-name))
;; If set-file-extended-attributes fails, fall back on
;; set-file-modes.
(unless
(with-demoted-errors "Error setting attributes: %s"
(set-file-extended-attributes buffer-file-name
(nth 1 setmodes)))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [1]
(set-file-modes buffer-file-name
(logior (car setmodes) 128)))))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [2]
------------------------- files.el -------------------------
The marked call [1] is a no-op, since it does not change the permissions
in any way when writing them back, while the call [2] to
`set-file-modes' actually changes the file mode.
Since an extended file attribute Elisp object cannot be modified yet (is
that so?) to mark it, for example, as writable, I propose to just drop
that call to `set-file-extended-attributes', like this:
------------------------- snip -------------------------
diff --git a/lisp/files.el b/lisp/files.el
index e1421b403bf..d4d556fa470 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -5944,14 +5944,8 @@ basic-save-buffer-2
"Error getting extended attributes: %s"
(file-extended-attributes buffer-file-name))
buffer-file-name))
- ;; If set-file-extended-attributes fails, fall back on
- ;; set-file-modes.
- (unless
- (with-demoted-errors "Error setting attributes: %s"
- (set-file-extended-attributes buffer-file-name
- (nth 1 setmodes)))
- (set-file-modes buffer-file-name
- (logior (car setmodes) 128)))))
+ (set-file-modes buffer-file-name
+ (logior (car setmodes) 128))))
(let (success)
(unwind-protect
(progn
------------------------- snip -------------------------
*** Issue B
But then there is another issue (?), probably even longer unnoticed. To
notice it, apply above patch, make, then execute the following test
case:
rm -f foo
echo foo > foo
chmod 0400 foo
./src/emacs -Q
Define the following advice on `write-region' to simulate a write error:
------------------------- snip -------------------------
(advice-add 'write-region :override
(lambda (&rest _) (error "No space left on device")))
------------------------- snip -------------------------
Then continue
C-x C-f foo RET
C-x C-q
bar
C-0 C-x C-s
=> File foo is write-protected; try to save anyway?
yes RET
=> No space left on device
Now check the permissions of file foo:
[emacs-master]$ ls -al foo
-rw------- 1 jschmidt jschmidt 7 Oct 14 20:33 foo
So the write permissions did not get removed again.
Here the root cause is that the `unwind-protect' around the
`write-region' in `basic-save-buffer-2' does not handle the no-backup
case separately. I would extend the clean-up form of the
`unwind-protect' to distinguish these both cases and handle the
no-backup case appropriately, here by trying first to set back the
extended attributes, then the regular ones.
*** What to do and where?
I can provide patches for both issues. Plus ERT tests.
I guess that would be in one changeset, since these are related.
Should I provide a separate patch fixing only issue A for emacs-29? Or
is that issue not relevant for emacs-29, given that it went unnoticed
for 12 years?
--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#66546: 30.0.50; save-buffer to write-protected file without backup fails |
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Date: |
Sat, 04 Nov 2023 14:59:14 +0200 |
> From: Jens Schmidt <jschmidt4gnu@vodafonemail.de>
> Cc: 66546@debbugs.gnu.org
> Date: Sat, 04 Nov 2023 13:30:37 +0100
>
> Eli Zaretskii <eliz@gnu.org> writes:
>
> > I think one nit is still missing:
>
> Right you are. Fixed in next version.
Thanks, installed on the master branch.
Can we close the bug now?
--- End Message ---