[vfio-users] Using input-linux in qemu-git; mouse works, but keyboard doesn't

William Green billcoder at gmail.com
Sun Apr 10 22:10:27 UTC 2016

Looks like this is a bug with the input-linux.  The function
"input_linux_complete" tries to detect what kind of input device the given
evdev device is by testing EVIOCGBIT(0, ...).  My keyboard (a Logitech
K350) has the EV_REL bit set, and so input_linux_complete sees it as a
mouse.  That explains my problems.

I'll see about reporting the bug to QEMU.


I installed the qemu-git AUR package on my Arch system, so that I could try
the new input-linux patches.  I use virt-manager, so I added this to the
XML for the Windows 10 guest using "virsh edit win10":

    <qemu:arg value='-object'/>
    <qemu:arg value='-object'/>
    <qemu:arg value='input-linux,id=mouse1,evdev=/dev/input/event2'/>

I also had to whitelist /dev/input/event1 and /dev/input/event2 in
/etc/libvirt/qemu.conf under "cgroup_device_acl" (I also chmod'd
/dev/input/event1 and 2 as 777.  Just trying to get things working right

After doing all that, the machine boots and grabs my mouse.  The mouse
works in the guest, but the keyboard does not respond.  The hotkey to
toggle control back to the host doesn't work.  The only way I can release
the mouse is to shutdown the VM.

There are no errors listed in /var/log/libvirt/qemu/win10.log.  I double
checked that event1 is the right dev by running evtest.  I see all my
keyboard events when I do that.  evtest sees KEY_LEFTCTRL and
KEY_RIGHTCTRL, so those keys work.  When I start the VM, evtest stops
showing events, so clearly qemu is grabbing the devices.  I've looked over
the code in input-linux.c and can't see why it wouldn't at least respond to
the hotkey.

I'm not sure how to do further debugging at this point.  I don't know the
QEMU codebase, so I don't know how to add logging to input-linux.c.  Not
sure if printing to stdout works or where that output would go.  I might
try adding a few printf statements to see if I can get QEMU to tell me if
it is at least receiving the keyboard events correctly or what's going on.

Any help would be appreciated, thank you.
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