From: Duncan Greatwood <dgreatwood@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 70973@debbugs.gnu.org
Subject: bug#70973: 29.1; "Unlocking file: Invalid argument" Warning saving via a softlink with stale file lock
Date: Thu, 16 May 2024 14:36:37 -0700 [thread overview]
Message-ID: <CAGg=3NVstcd_hE3N5VNjj30uFN8hBEqDXPaTK-_v737hQ5L03g@mail.gmail.com> (raw)
In-Reply-To: <86msoph6wt.fsf@gnu.org>
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I would agree that the issue was likely due to a system crash at an
inopportune moment.
Of course, if emacs did detect a bad lock file, it could prompt the user
for confirmation before removing / replacing it. No need to be silent.
The status quo, requiring a user to find and remove the lock file manually,
seems burdensome to my eye, albeit the issue is presumably rare. But
certainly it is a matter of taste.
On Thu, May 16, 2024 at 12:52 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Duncan Greatwood <dgreatwood@gmail.com>
> > Date: Thu, 16 May 2024 12:27:05 -0700
> > Cc: 70973@debbugs.gnu.org
> >
> > I just tried editing a different file, client.cc, causing a lockfile to
> be created. Sure enough, just as you say, that
> > lockfile is a dangling symlink:
> > ls -al .#client.cc
> > lrwxr-xr-x@ 1 username staff 40 May 16 11:39 .#client.cc ->
> username@DMG-MB-Air-15-2024.local.3071
> >
> > Then, returning to editing ~/.emacs (which, being a symlink, is actually
> editing ~
> > /Dropbox/Documents/Projects/emacs/dotemacs).
> > Again, this creates a dangling symlink as you would expect:
> > ls -l .#dotemacs
> > lrwxr-xr-x@ 1 username staff 40 May 16 11:43 .#dotemacs ->
> username@DMG-MB-Air-15-2024.local.3071
> >
> > At this point, I tried doing a hard reboot (power cycle) to simulate the
> kernel crash I mentioned before. But
> > (not surprisingly) after the reboot the lock file still looks as you
> would expect.
> > ls -l .#dotemacs
> > lrwxr-xr-x@ 1 username staff 40 May 16 11:43 .#dotemacs ->
> username@DMG-MB-Air-15-2024.local.3071
> >
> > Noting that, in the bad case, the lock file was not only not a dangling
> symlink as it should be, but was also of
> > zero size, I would speculate that the kernel crash happened right as
> emacs was part way through writing the
> > lockfile to disk.
> >
> > Taking a quick look at the emacs source, the C function create_lock_file
> calls emacs_symlink which in turn
> > calls the OS function symlink.
> >
> > The OS function symlink is commonly assumed to be atomic I believe (e.g.
> see
> > https://rcrowley.org/2010/01/06/things-unix-can-do-atomically.html).
> However in this case I would suspect that
> > the kernel crash terminated the symlink write before it could fully
> complete.
> >
> > To fix, perhaps emacs needs to check purported lock files and handle the
> case where they are not symlinks
> > and/or are of zero size, avoiding the need to remove the
> partially-written lock file manually.
>
> I'm not sure we should silently sweep these rare and special cases
> under the carpet. The warning is just a warning, and manually
> deleting the lock file fixes even that.
>
> So I'm not sure we should do anything here, as long as the conclusion
> is that this happened due to a system crash in an opportune moment.
>
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next prev parent reply other threads:[~2024-05-16 21:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-16 0:53 bug#70973: 29.1; "Unlocking file: Invalid argument" Warning saving via a softlink with stale file lock Duncan Greatwood
2024-05-16 8:43 ` Eli Zaretskii
2024-05-16 14:17 ` Duncan Greatwood
2024-05-16 15:46 ` Eli Zaretskii
2024-05-16 15:55 ` Duncan Greatwood
2024-05-16 16:09 ` Eli Zaretskii
2024-05-16 16:20 ` Duncan Greatwood
2024-05-16 18:18 ` Eli Zaretskii
2024-05-16 19:27 ` Duncan Greatwood
2024-05-16 19:51 ` Eli Zaretskii
2024-05-16 21:36 ` Duncan Greatwood [this message]
2024-06-01 14:04 ` Eli Zaretskii
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