[Bug 107309] libGL error: MESA-LOADER: failed to retrieve device information on virgl

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107309

            Bug ID: 107309
           Summary: libGL error: MESA-LOADER: failed to retrieve device
                    information on virgl
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libdrm
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: vliaskovitis at suse.com

Created attachment 140732
  --> https://bugs.freedesktop.org/attachment.cgi?id=140732&action=edit
xf86drm: Correctly parse pci device information for virtio gpu

Mesa 18.1.3-201.1
kernel 4.17.5-1-default
libdrm 2.4.92-1.2

glxinfo | grep -i renderer
OpenGL renderer string: virgl

LIBGL_DEBUG=verbose glxgears
libGL error: MESA-LOADER: failed to retrieve device information
libGL: using driver virtio_gpu for 4
libGL: OpenDriver: trying /usr/lib64/dri/tls/virtio_gpu_dri.so
libGL: OpenDriver: trying /usr/lib64/dri/virtio_gpu_dri.so

Adding some debug drmMsg() prints, I found that the MESA-LOADER error message
happens because drmGetDevice2() returns -ENODEV. And that happens because
drmParseSubsystemType() returns -EINVAL.

drmParseSubsystemType() expects /sys/dev/char/DRM_MAJOR\:0/device/subsystem to
be one of pci, usb, platform, hostix. But virtio-gpu has bus subsystem virtio:

ls -al /sys/dev/char/226\:0/device/subsystem
lrwxrwxrwx 1 root root 0 Jul 19 17:39 /sys/dev/char/226:0/device/subsystem ->
../../../../bus/virtio

ls -al /sys/dev/char/226\:128/device/subsystem
lrwxrwxrwx 1 root root 0 Jul 19 17:39 /sys/dev/char/226:128/device/subsystem ->
../../../../bus/virtio

I am not sure if this is a cosmetic error, or if it matters. I am attaching a
proposed patch.

Since the virtio-gpu device is actually a pci device, we can still parse the
correct information from the corresponding pci device:

ls -al /sys/dev/char/226\:0
lrwxrwxrwx 1 root root 0 Jul 20 13:30 /sys/dev/char/226:0 ->
../../devices/pci0000:00/0000:00:02.0/virtio0/drm/card0

i.e. use /sys/dev/char/226\:128/../../../ instead of /sys/dev/char/226\:128/
for virtio devices.

to parse subsystem, and subsequently pci bus and pci device information.

(Let me know if bugzilla is still the place to report bugs, or if 
https://gitlab.freedesktop.org/mesa/drm is now the preferred location)

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