Re: udmabuf error with libvirt + QEMU

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On Tue, Feb 01, 2022 at 02:27:55PM +0000, M, Shivakumar wrote:
> Hi,
> We are seeing an issue with udambuf, where it says "open /dev/udmabuf: No such file or directory " even if the device exits. This issue particularly we are seeing with libvirt. When we run the QEMU args on the command line, everything works as expected.
> It seems to be some permission issue when we use the Libvirt, please help us on resolving this.

When libvirt launches QEMU it puts in place a number of strict
security protections. Libvirt will grant access on a per-file
basis to resources on the host that QEMU should be allowed to
access based on the device configuration in the XML.

In your case though you're using command line passthrough:

>   <qemu:commandline>
>     <qemu:arg value="-device"/>
>     <qemu:arg value="virtio-vga,blob=true"/>
>     <qemu:arg value="-display"/>
>     <qemu:arg value="gtk,gl=on"/>
>     <qemu:env name="DISPLAY" value=":1.0"/>
>   </qemu:commandline>

This is totally opaque to libvirt and so libvirt won't be
granting access to any resources needed by these args. I'm
assuming /dev/udmabuf is needed by the GTK display for GL
support, or something along those lines.

For further information about your options please consult this page:

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