bug#53432: [PATCH] Avoid losing keyboard input when inotify is too busy

[Eli Zaretskii <eliz@gnu.org>]

> From: Ian Jackson <ijackson@chiark.greenend.org.uk>
> Date: Fri, 21 Jan 2022 23:36:01 +0000
> 
> I experienced a bug where my Emacs (Debian's emacs-lucid) would lose
> keystrokes under pathological conditions.  I tracked this down to the
> keyboard input buffer filling up with inotify events.
> 
> The attached patches have been rebased onto emacs-28 (fbc9b121e062)
> and I have tested before-and-after versions in parallel to verify that
> the bug appears in the upstream branch and has been fixed with my
> patches.
> 
> The bug was really quite severe in my (rather abusive) situation, with
> Debian's emacs-lucid 26.1.  With the upstream emacs-28 branch it
> requires more effort, and loses fewer keys.  I suspect that some more
> sophisticated approach to inotify requests means it's harder to get
> the buffer to fill up with the newer version.  Unfortunately I am not
> able to share my whole repro, but a key part is to visit the output
> file from this
>   while yes | dd of=t bs=1 count=1000000; do : ;
> with global-auto-revert-mode enabled.
> 
> With my patches it is still possible to get emacs to perform very
> poorly by abusing it this way, but at least all the keys arrive
> eventually.  I added some FIXMEs for further work that would be good,
> but is not critical to fixing the bug.

Thanks.  I doubt that we want to complicate our input handling this
way on behalf of "abusing" inotify.  File notifications are known not
to be scalable enough to support global-auto-revert-mode well.

In any case, installing this on the emacs-28 branch is out of the
question: it's too late for that.  We may install some variant of this
on master, after discussing how best to handle this.  Po Lu's
suggestion to stop processing inotify events sounds better to me.

> I hope the commit messages are in the expected format.  I think I
> probably have GNU copyright paperwork on file already, perhaps under a
> different email address.

I don't see your name or email address on file, so maybe they are both
different?