Bug#983357: Netinst crashes xen domU when loading kernel

[Chuck Zmudzinski]

On 5/24/2021 3:30 AM, Michael Biebl wrote:
> Hi Phillip
>
> Am 24.05.2021 um 06:19 schrieb Cyril Brulebois:
>>> trigger to cold plug all devices.  Both scripts are set -e.  The Xen
>>> Virtual Keyboard driver and at least one other driver have always 
>>> failed
>>> to trigger due to having absurdly long modalias, but the error used to
>>> be ignored.  The kernel now returns the error to udevadm
>
> So this is a change in behaviour in the kernel?
> What happens if you boot the installed system? Does udevadm trigger 
> fail there as well?
>
> I feel a bit uneasy changing the udev start script this late in the 
> release cycle (especially when it appears like covering up an issue 
> someplace else).
>
> I'll let Marco make the judgement on this though, as he has the most 
> experience with those udev udeb start scripts as the original author.
>
> Michael
>

After reviewing Philip's message at

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=983357#43

which seems to point to the root cause of this bug, I can add:

On my Xen HVM DomU I see the absurdly long modalias for the Xen
Virtual keyboard that seems to be causing this crash in sysfs at

/sys/devices/virtual/input/input2/modalias

But at /sys/devices/vkbd-0/modalias, I see just 'xen:vkbd', which would
probably not result in an error in the udev script if this was also
written as the modalias at /sys/devices/virtual/input/input2/modalias

So the Xen virtual keyboard appears more than once in sysfs, and
modalias is not the same in the different places. This seems
to be a problem.

I understand the correct way to fix this bug is by modifying the
Xxen virtual keyboard (and any other devices that might cause
this crash) and not the start-udev script on the netinst
installation media, which is so far the only available workaround.
Hopefully Xen will accept a fix if we can come up with a fix.

I am willing to try to debug this by testing patches to the Xen
virtual keyboard, and anyone who has any tips on how
udev works would be helpful. Is there documentation in udev for
device developers somewhere to consult that explains how to
update old device drivers so they are compatible with the
modern version? Does the Xen virtual keyboard need to be
managed by udev? Is there a simple way to disable incompatible
devices so udev ignores them?

Chuck Zmudzinski