Package: emacs;
Reported by: Jonathan Tomer <jktomer <at> google.com>
Date: Mon, 29 Apr 2019 23:32:01 UTC
Severity: normal
Tags: patch
Done: Michael Albinus <michael.albinus <at> gmx.de>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Jonathan Tomer <jktomer <at> google.com> To: 35497 <at> debbugs.gnu.org Cc: Jonathan Tomer <jktomer <at> google.com> Subject: bug#35497: [PATCH v2] Don't rewrite buffer contents after saving by rename Date: Tue, 30 Apr 2019 17:26:42 -0700
When `file-precious-flag' is non-nil, files are saved by renaming a
temporary file to the new name; this is an atomic operation on POSIX
so other programs will not see the file in an intermediate state.
Unfortunately, due to a paren-matching error introduced in change
574c05e219476912db3105fa164accd9ba12b35f, we would then write the
contents again in the usual way after this rename. In addition to
being wasteful, this is a serious bug: the whole point of
`file-precious-flag' is to prevent race conditions with other programs
that might otherwise see an empty file, but with this bug the race is
actually much *more* likely to be visible: the rename will alert any
inotify watchers of a change, and then the subsequent write is very
likely to truncate the file just as those programs start to read it!
* lisp/files.el (basic-save-buffer-2): Don't rewrite file contents
after saving-by-renaming.
* test/lisp/files-tests.el (files-tests-dont-rewrite-precious-files):
* test/lisp/net/tramp-tests.el (tramp-test46-file-precious-flag):
Regression tests for this change.
---
lisp/files.el | 4 ++--
test/lisp/files-tests.el | 26 ++++++++++++++++++++++++++
test/lisp/net/tramp-tests.el | 28 ++++++++++++++++++++++++++++
3 files changed, 56 insertions(+), 2 deletions(-)
diff --git a/lisp/files.el b/lisp/files.el
index c05d70a00e..72518e8127 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -5256,7 +5256,7 @@ basic-save-buffer-2
(set-file-extended-attributes buffer-file-name
(nth 1 setmodes)))
(set-file-modes buffer-file-name
- (logior (car setmodes) 128))))))
+ (logior (car setmodes) 128)))))
(let (success)
(unwind-protect
(progn
@@ -5272,7 +5272,7 @@ basic-save-buffer-2
(and setmodes (not success)
(progn
(rename-file (nth 2 setmodes) buffer-file-name t)
- (setq buffer-backed-up nil))))))
+ (setq buffer-backed-up nil)))))))
setmodes))
(declare-function diff-no-select "diff"
diff --git a/test/lisp/files-tests.el b/test/lisp/files-tests.el
index ae8ea41a79..15f2a760c4 100644
--- a/test/lisp/files-tests.el
+++ b/test/lisp/files-tests.el
@@ -1244,5 +1244,31 @@ files-tests-file-attributes-equal
(executable-find (file-name-nondirectory tmpfile))))))
(delete-file tmpfile))))
+(ert-deftest files-tests-dont-rewrite-precious-files ()
+ "Test that `file-precious-flag' forces files to be saved by
+renaming only, rather than modified in-place."
+ (files-tests--with-temp-file temp-file-name
+ (let* (temp-file-events
+ (watch (file-notify-add-watch
+ temp-file-name '(change)
+ (lambda (event)
+ (push (cadr event) temp-file-events)))))
+ (unwind-protect
+ (with-current-buffer (find-file-noselect temp-file-name)
+ (setq-local file-precious-flag t)
+ (insert "foobar")
+ (should (null (save-buffer)))
+
+ ;; file-notify callbacks are triggered by input events,
+ ;; so we need to accept input before checking results.
+ (with-timeout (3.0 (ignore))
+ (while (read-event nil nil 0.01) (ignore)))
+
+ ;; When file-precious-flag is set, the visited file
+ ;; should never be modified, only renamed-to (which may
+ ;; appear as "renamed" and/or "created" to file-notify).
+ (should (not (memq 'changed temp-file-events))))
+ (file-notify-rm-watch watch)))))
+
(provide 'files-tests)
;;; files-tests.el ends here
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index cba697da18..1ca98520b3 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -44,6 +44,7 @@
(require 'dired)
(require 'ert)
(require 'ert-x)
+(require 'filenotify)
(require 'tramp)
(require 'vc)
(require 'vc-bzr)
@@ -5741,6 +5742,33 @@ tramp--test-asynchronous-requests-timeout
(ignore-errors (all-completions "tramp" (symbol-value x)))
(ert-fail (format "Hook `%s' still contains Tramp function" x))))))
+(ert-deftest tramp-test46-file-precious-flag ()
+ "Check that file-precious-flag is respected with Tramp in use."
+ (let* ((temp-file (make-temp-file "emacs"))
+ (remote-file (concat "/mock:localhost:" temp-file))
+ temp-file-events
+ (watch
+ (file-notify-add-watch
+ temp-file '(change)
+ (lambda (event)
+ (push (cadr event) 'temp-file-events)))))
+ (unwind-protect
+ (with-current-buffer (find-file-noselect remote-file)
+ (setq-local file-precious-flag t)
+ (insert "foobar")
+ (should (null (save-buffer)))
+
+ ;; file-notify callbacks are triggered by input events, so
+ ;; we need to accept input before checking results.
+ (with-timeout (3.0 (ignore))
+ (while (read-event nil nil 0.01) (ignore)))
+
+ ;; When file-precious-flag is set, the visited file should
+ ;; never be modified, only renamed-to.
+ (should (not (memq 'changed temp-file-events)))))
+ (file-notify-rm-watch watch)
+ (delete-file temp-file)))
+
(defun tramp-test-all (&optional interactive)
"Run all tests for \\[tramp]."
(interactive "p")
--
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