bug#66381: 29.1; Auto-revert not polling files when notifications are enabled

[Michael Albinus]

Eli Zaretskii <eliz@gnu.org> writes:

Hi Eli,

>> I've checked the other file notification backends, and it turns out,
>> that none of them reports unmount events. So I have extended the patch,
>> the unmount event is propagated now in all backends (under different
>> event names), and it causes to stop the respective file notification
>> watch.
>>
>> This works for all but the w32notify backend. I dont know whether this
>> library supports a kind of unmount events, and even in case it does, I
>> wouldn't be able to implement this. Eli, do we want to do something
>> here?
>
> I don't know, I will have to test this.
>
> Could you please help me by showing some Lisp I could use to see if
> unmounting a volume gets reported in some way to the
> file-notifications machinery?  I have very little free time these
> days, for more than one good reason, but would like not to postpone
> investigating this for too long, which will happen if I need to find
> the recipe myself.  TIA.

I would apply the following recipe:

- Use a mounted share. In my environment, "z:" is a Samba mount.

- Call

--8<---------------cut here---------------start------------->8---
$ emacs -l filenotify --eval '(setq file-notify-debug t)' --eval 
'(file-notify-add-watch "z:/123" (quote (change attribute-change)) (quote 
ignore))'
--8<---------------cut here---------------end--------------->8---

- In another shell outside Emacs, call

--8<---------------cut here---------------start------------->8---
$ touch z:/123
--8<---------------cut here---------------end--------------->8---

- You'll see in Emacs the messages

--8<---------------cut here---------------start------------->8---
file-notify-handle-event (file-notify (541405157192 modified "123") 
file-notify--callback-w32notify)
file-notify-callback 541405157192 changed "z:/123" nil #s(file-notify--watch 
"z:/" "123" ignore) "z:/123" "z:/"
--8<---------------cut here---------------end--------------->8---

- Unmount the share. There shall be another file notification, but there
  isn't.

In a similar scenario I use with Emacs/inotify, I see the meesages

--8<---------------cut here---------------start------------->8---
file-notify-handle-event (file-notify ((1 . 0) (attrib) "123" 0) 
file-notify--callback-inotify)
file-notify-callback (1 . 0) attribute-changed 
"/tmp/tramp.sshfs.detlef/home/albinus/123" nil #s(file-notify--watch 
"/tmp/tramp.sshfs.detlef/home/albinus" "123" ignore) 
"/tmp/tramp.sshfs.detlef/home/albinus/123" 
"/tmp/tramp.sshfs.detlef/home/albinus"
file-notify-handle-event (file-notify ((1 . 0) (unmount isdir) 
"/tmp/tramp.sshfs.detlef/home/albinus" 0) file-notify--callback-inotify)
file-notify-handle-event (file-notify ((1 . 0) stopped 
"/tmp/tramp.sshfs.detlef/home/albinus/123") ignore)
file-notify-handle-event (file-notify ((1 . 0) (ignored) 
"/tmp/tramp.sshfs.detlef/home/albinus" 0) file-notify--callback-inotify)
--8<---------------cut here---------------end--------------->8---

"/tmp/tramp.sshfs.detlef" is the mount point in that case.

Best regards, Michael.