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

[Ian Jackson]

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.

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.

Regards,
Ian.

0001-inotify.c-Document-hazard-of-unlimited-buffering.patch
Description: Binary data

0002-inotify.c-Use-a-buffer-from-the-heap.patch
Description: Binary data

0003-inotify.c-Break-out-inotify_process_buffer.patch
Description: Binary data

0004-inotify-Pause-when-keyboard-input-is-suspended.patch
Description: Binary data

-- 
Ian Jackson <ijackson@chiark.greenend.org.uk>   These opinions are my own.  

Pronouns: they/he.  If I emailed you from @fyvzl.net or @evade.org.uk,
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