Bug 1166319

+++ This bug was initially created as a clone of Bug #1153377 +++

When connecting to a guest with virt-viewer using the custom monitor mapping feature, guest displays can be swapped incorrectly. Issue noted by David Jasa in bug 1129477 comment 29 (copied here):

> Jonathon, would it be able to rearrange guest monitor layout as well to
> match client layout? E.g.:
> 
> monitor-mapping=1:2;2:1 with client layout:
> 
> +---+---+
> | 1 | 2 |
> +---+---+
> 
> will produce also guest layout:
> 
> +---+---+
> | 1 | 2 |
> +---+---+
> 
> leading to non-contiguous guest desktop in fullscreen:
> 
> +------------+-----------+
> |------+     |  +--------|
> |INDOW |     |  | GUEST W|
> |------+     |  +--------|
> +------------+-----------+
> 
> so the guest layout should be:
> 
> +---+---+
> | 2 | 1 |
> +---+---+
> 


The client sends down the correct arrangement, but it apparently gets swapped somehow by either the host or the guest.

--- Additional comment from RHEL Product and Program Management on 2014-10-15 18:07:05 EDT ---

Since this bug report was entered in bugzilla, the release flag has been
set to ? to ensure that it is properly evaluated for this release.

--- Additional comment from Jonathon Jongsma on 2014-10-21 11:38:34 EDT ---

debug output enabled with

echo 0x4 > /sys/module/drm/parameters/debug

At the top of the log, you can see that it reads the configuration correctly (pay attention to the x offsets):

[584886.586655] [drm:qxl_display_copy_rom_client_monitors_config] read 1600x900+1680+0
[584886.586660] [drm:qxl_display_copy_rom_client_monitors_config] read 1680x1050+0+0

But later on, it sets the display config to the wrong values. For display 0:

[584887.126824] [drm:qxl_monitors_config_set] 0:1600x900+0+0

and display 1:

[584887.129141] [drm:qxl_monitors_config_set] 1:1680x1050+1600+0

--- Additional comment from Jonathon Jongsma on 2014-10-22 16:59:12 EDT ---

In fact, it appears that when using the new method of display configuration (i.e. hotplug events instead of the vdagent, introduced in RHEL 7, Fedora 19 (or 20?), etc), the monitors appear to always be arranged left-to-right by display ID rather than using the coordinates passed down by the client. Still investigating...

--- Additional comment from Christophe Fergeau on 2014-10-23 04:08:12 EDT ---

In fedora 20, the way hotplug events are handled in mutter could cause that as the position from the config is not used, but rather we let mutter do the layout through make_default_config() in src/core/monitor-config.c (mutter 3.10.4). I have started some patches to bypass this and directly use the monitor config we got, but it's not finished yet (only taking into account resolution, not position).
RHEL7 did not have that code in mutter though, so I don't know if something equivalent is done, and this has changed in f21 too.

--- Additional comment from Jonathon Jongsma on 2014-10-23 11:00:05 EDT ---

yeah, I've been looking at this in rhel7. I suspect a similar thing is happening within gnome-settings-daemon xrandr plugin.

--- Additional comment from Jonathon Jongsma on 2014-10-23 17:51:24 EDT ---

So, it appears that it's not currently possible control layouts with this hotplug method. There's no real way to communicate a desired position for a display from the kernel to userspace. So the guest simply arranges the displays as it sees fit. Some comments from Dave Airlie on IRC:

<airlied> we probably just want to expose a couple of new properties from the kernel
<airlied> with a suggested x/y position then change userspace to take notice of them
<airlied> rather than doing something too spice specific

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:40:31 EST ---

upstream patches to mutter are attached to https://bugzilla.gnome.org/show_bug.cgi?id=740069.

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:49:39 EST ---

Adds ability to determine whether output has hotplug_mode_update property

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:50:23 EST ---

Adds the ability to get the suggested position for an output

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:51:45 EST ---

Uses the suggested position for an output to arrange displays

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:52:24 EST ---

don't apply stored configuration for outputs with hotplug_mode_update

--- Additional comment from Jonathon Jongsma on 2014-11-18 15:54:23 EST ---

I've attached patches required to backport this feature to rhel 7.1. The upstream code for handling monitor configuration has changed considerably since RHEL 7.1. It now happens exclusively in mutter, whereas in RHEL 7.1, it is distributed between libgnome-desktop and gnome-settings-daemon.




Required patches:

attachment 958761 [details]
attachment 958764 [details]