Bug#983357: (no subject)

[Phillip Susi <phill@thesusis.net>]

I bisected the problem to this commit:

commit df44b479654f62b478c18ee4d8bc4e9f897a9844
Author: Peter Rajnoha <prajnoha@redhat.com>
Date:   Wed Dec 5 12:27:44 2018 +0100

    kobject: return error code if writing /sys/.../uevent fails
    
    Propagate error code back to userspace if writing the /sys/.../uevent
    file fails. Before, the write operation always returned with success,
    even if we failed to recognize the input string or if we failed to
    generate the uevent itself.
    
    With the error codes properly propagated back to userspace, we are
    able to react in userspace accordingly by not assuming and awaiting
    a uevent that is not delivered.
    
    Signed-off-by: Peter Rajnoha <prajnoha@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

So it appears that the Xen Virtual Keyboard driver was always broken but
the error in triggering the uevent was not previously reported.  The
upstream bug report notes another driver failing.  There are probably
other drivers too. 

I will continue to try to find and fix the Xen keyboard error so it no
longer fails anyway, but it is probably a good idea to patch the
start-udev script in d-i to ignore errors.  It is better to continue
with some device not triggering a cold plug event than to instantly panic
the kernel in early boot.