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SubjectRe: commit 83d817f410 broke my ability to use Linux with a braille display
On Fri, Jan 11, 2019 at 01:33:09PM -0500, Nicolas Pitre wrote:
> I use Linux with the help of a braille display and the brltty daemon. It
> turns out that the latest mainline kernel I can work with comes from
> commit 231f8fd0cc. Anything past that and I lose the ability to read the
> console barely a few seconds after the system has booted as brltty is
> thrown a wrench and the braille display becomes completely inoperable.
>
> Things get somewhat better with commit c96cf923a9 as brltty is not
> longer incapacitated, but some programs would randomly crash. Even the
> very first login attempt won't work as I soon as I hit enter after my
> user name the password prompt is skipped over, just like if the enter
> key had been hit twice. Then lynx (the text web browser) would crash as
> soon as I switch the virtual console with LeftAlt+FN. Mind you, this
> isn't easy to perform bisection in those conditions.
>
> And the worst commit i.e. 83d817f410 is marked for stable! :-(
>
> Some interaction with brltty must be at play here otherwise such
> breakage would never have survived up to the mainline kernel.
>
> As far as latest mainline is concerned, I managed to reproduce at least
> one of the unwelcome behavior change (hoping that's all there is to this
> issue) with a very simple test case so you won't have to learn braille
> to debug this:
>
> # from any vt, make sure tty40 is allocated and empty
> openvt -c 40 -f -- true
>
> # open it and wait on read()
> cat /dev/tty40
>
> # from a second vt, simply open tty40 again
> true < /dev/tty40
>
> # come back to the first vt and watch cat bailing out with EAGAIN.
>
> Please fix.
>
>
> Nicolas


This all sounds familiar, and I suspect this is the fix:

https://lkml.org/lkml/2019/1/8/1379

Regards,
Vito Caputo

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