Bug 493623 - The evdev driver needs to understand xkb
The evdev driver needs to understand xkb
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: xorg-x11-drv-evdev (Show other bugs)
All Linux
low Severity medium
: rc
: ---
Assigned To: Peter Hutterer
Depends On:
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Reported: 2009-04-02 08:45 EDT by john.haxby@oracle.com
Modified: 2009-07-31 10:44 EDT (History)
0 users

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2009-07-30 14:28:47 EDT
Type: ---
Regression: ---
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RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
A patch to add xkb support xorg-x11-evdev (11.16 KB, patch)
2009-04-02 08:45 EDT, john.haxby@oracle.com
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  None (edit)
Description john.haxby@oracle.com 2009-04-02 08:45:19 EDT
Created attachment 337795 [details]
A patch to add xkb support xorg-x11-evdev

Description of problem:

If you try to configure the Xen virtual mouse/keyboard combination device you discover that you need stanzas like this in the xorg.conf config file:

Section "InputDevice"
        Identifier  "Keyboard0"
        Driver      "kbd"
        Option      "XkbModel" "evdev"
        Option      "XkbLayout" "gb"

Section "InputDevice"
        Identifier  "xeninput"
        Driver      "evdev"
        Option      "Device" "/dev/input/event0"
        Option      "SendCoreEvents" "True"
        Option      "XkbModel" "evdev"
        Option      "XkbLayout" "gb"

(This can be automated: with patches to rhpl and rhpxl one can use system-config-display the user does not need to be concerned with actually getting this
lot right.)   The problem here is that while the "xeninput" device that uses evdev is only actually needed to get pointer tracking correctly (so that you get absolute coordinates instead of relative ones).

Ideally you'd just have the one InputDevice which is both a pointer and a
keyboard, but the X server gets confused and spits out a _lot_ of warning
messages (one for every mouse and/or keyboard event) if you try to combine
these.  Even worse, although the Xkb settings are on a per-device setting you
can't actually have different xkb settings for different devices if you want
things to work.

Version-Release number of selected component (if applicable): xorg-x11-drv-evdev-

How reproducible:  Always

Steps to Reproduce:
1.  Attempt to configure the Xen virtual keyboard/mouse combination device as

Actual results:

You can't do it.  Or if you can xkb doesn't work.  Or the mouse doesn't work. 
Or the keyboard doesn't work.  Or both.  Or you get a _lot_ of warning messages
from the X server.
Comment 1 john.haxby@oracle.com 2009-04-02 09:59:00 EDT
Related bugs: bug 493618, bug 493623, bug 493627, bug 493630, bug 493634 and bug 493642
Comment 2 Markus Armbruster 2009-07-30 14:28:47 EDT
The bug as reported is about the difficulties to manually configure X
in a certain way, to get proper pointer tracking.  It is certainly
valid.  However, the real problem users care about is that pointer
tracking works very poorly (mouse hits invisible wall).

Upstram, we solved the problem by fixing numerous issues in various
places to make it work out of the box, from Fedora 11 on.

The patches proposed by the reporter solve the problem by making
manual configuration work.  They are unrelated to the upstream

Like the upstream solution, they're fairly invasive: they touch the
kernel and several user space packages.  This is a significant risk.
Moreover, splitting the device is an ABI change.  The question is
whether there are benefits to justify that.

We already put much less invasive changes into 5.4 to improve pointer
tracking (bug 492866).  They fix the "mouse hits invisible wall"
problem.  They still require a pointer grab, which virt-viewer makes
relatively painless.

So, the benefit of the proposed patches over what we've got already is
to enable manual configuration so that the mouse grab can be avoided.
While that's certainly nice, it doesn't justify the risk, in my

If you disagree, please reopen the bug.

Some technical background:

There are 3 pieces in the stack: VNC client, QEMU VNC server and the
guest's X.  The old, misbehaving setup has VNC client sending absolute
coordinates, which the VNC server sends through xenkbd to X.  X in
RHEL-5 doesn't have any auto-configuration of input devices, so it
just opens /dev/input/mice, and thus the guest kernel converts from
absolute to relative.  Because the VNC client has no knowledge of this
conversion, you get into situation where you hit an invisible wall in
the client when it thinks it has got to the virtual desktop boundary.

Now, if you had absolute coordinates being passed and used all the way
to X then it would trivially work, but this requires X configuration.
Recent X's do that automatically.  RHEL-5's X simply isn't capable of
that.  The patches proposed by the reporter add manual configuration
steps across a wide range of RPMs.

The fix we did for RHEL-5.4 is to make xenkbd *not* use absolute
coordinates, so the VNC server now sends relative coordinates.  This
removes the broken absolute -> relative conversion in the guest
kernel.  On its own this isn't sufficient, because you then get broken
absolute to relative conversion in the VNC server instead.  So we also
added the VNC relative mouse extension to QEMU and GTK-VNC.  Now the
VNC client is in charge of doing the absolute -> relative conversion.
This is good, as this is the only point in the stack capable of doing
the conversion correctly, to avoid hitting an invisible wall.  The
only restriction is that you must grab the host mouse pointer and hide
it, so you only see the guest drawn pointer.
Comment 3 Markus Armbruster 2009-07-31 10:44:58 EDT
By the way, RHEL-6 pointer tracking will be fine out of the box using absolute coordinates, just like upstream.

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