[BRLTTY] brltty input monitor error 19

[Colomban Wendling]

Hello everyone,

A client of mine is having trouble with brltty sometimes heavily 
spamming the logs with "braille input monitor error 19: No such device", 
and I'm wondering what this could actually mean is the trouble.

Also, by spamming I mean like a lot, for the last week alone he's got 
more than 17 million lines matching that in syslog (~500k one day, 9.1M 
another, and 7.6M yesterday).  When it happens, it spams insanely fast, 
I can count around 50k messages/second for about 5s at a time.

The client is running Debian 10 "Buster" (yeah I know, it's not 
up-to-date), which is brltty 5.6.10+deb10u1 [1].

As a workaround, I currently set "log-level critical" to try and not get 
these errors in the logs, as their rate managed to fill /var/log [2]; 
and because the client didn't seem to actually have issues with his 
braille device.

Does anybody here have clues on:
* why does it happen?  Is something *actually* wrong, just going 
unnoticed by the user?
* was it a bug that has been fixed in newer releases?  I know the client 
isn't using the latest version, but I'm slightly reluctant to update it 
just yet unless I can reasonably hope it actually fixes the issue.

Thanks for your attention, and looking forward to reading you :)
Colomban

[1]: This is brltty 5.6.10 with a few Debian patches -- mostly backports 
of specific relevant commits IIUC 
(https://salsa.debian.org/a11y-team/brltty/-/tree/debian-buster/debian/patches?ref_type=heads)
[2]: which is another issue that it can actually happen, but unrelated 
to brltty