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

Bob Dawes xochipilli4 at yahoo.com
Mon Apr 11 00:50:48 UTC 2016

Just a quick thought as I personally find the layout of evdev terminally 
confusing but given evdev likes to have lots and lots of events numbers 
for every device it does seem likely that your keyboard / mouse wouldn't 
be event1/event2 as something else would beat them to it. Do you have a 
/dev/input/by-id directory as I do on my debian/arch systems? I find it 
gives readable names that don't change randomly all the time and are 
links to the concisely . They are still confusing though.

ls -l /dev/input/by-id/
total 0
lrwxrwxrwx 1 root root 9 Apr 10 20:29 usb-Areson_USB_Device-event-mouse 
-> ../event3
lrwxrwxrwx 1 root root 9 Apr 10 20:29 
usb-Areson_USB_Device-if01-event-kbd -> ../event4
lrwxrwxrwx 1 root root 9 Apr 10 20:29 usb-Areson_USB_Device-mouse -> 
lrwxrwxrwx 1 root root 9 Apr 11 00:54 
usb-Logitech_USB_Keyboard-event-if01 -> ../event7
lrwxrwxrwx 1 root root 9 Apr 11 00:54 
usb-Logitech_USB_Keyboard-event-kbd -> ../event6

In this case event4 is particularly confusing as it is a mouse in "media 
keys," clothing.

To double check type cat /proc/bus/input/devices and look for the 
Handlers lines as these should match the above. It should say things 
like kbd event7 (and it matches) and you can pick up the device 
names/sysfs fields from the structure and prod them further to be sure

It's 1:30 am ... so if you get stuck send me a direct mail with

ls -l /dev/input/by-id
cat /proc/bus/input/devices
xinput list --long

And I'll tell you precisely about why I don't know what the hell is 
going on. I have done it before ... just seemed a long tim ago. It's 
really not that bad either .. I'm pretty sure it just got tidied up 
recently hence my personal trauma as nothing tht used to work does anymore.

> 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.
>     Hello,
>     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:commandline>
>         <qemu:arg value='-object'/>
>         <qemu:arg
>     value='input-linux,id=kbd1,evdev=/dev/input/event1,grab_all=on'/>
>         <qemu:arg value='-object'/>
>         <qemu:arg value='input-linux,id=mouse1,evdev=/dev/input/event2'/>
>       </qemu:commandline>
>     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 now).
>     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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> vfio-users at redhat.com
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