[virglrenderer-devel] [PATCH 0/4] Provide the means to inject info about the host GL into a qemu guest

[Gert Wollny]

Am Donnerstag, den 14.06.2018, 08:57 +0200 schrieb Gerd Hoffmann:
> On Thu, Jun 14, 2018 at 12:54:31PM +1000, Dave Airlie wrote:
> > On 13 June 2018 at 19:03, Gert Wollny <gert.wollny at collabora.com>
> > wrote:
> > > Dear all,
> > > 
> > > this is a reworked proposal to make it possible to obtain
> > > information about
> > > the host GL and virglrender version from within the guest. The
> > > series doesn't
> > > require any changes to the guest version of virgl or to qemu.
> > > Instead it
> > > provides the means to inject this information into the guest
> > > system by using
> > > smbios OEM strings.
> > 
> > Interesting idea, I'd like to know what the qemu devs think of this
> > approach.
> > 
> > The having an external program and having to have qemu call it
> > seems
> > like it might be a bit restrictive, though it does mean we don't
> > have to change
> > qemu to get the info in the guest, which is nice.
> 
> Well, except that you have to do the change higher up the stack then
> (libvirt or whatever else starts qemu).  Getting the egl vs. glx
> thing right is left as an excercise to the qemu caller too.
It is essentially a feature to be used when debugging and fixing bugs
and adding new features, when one might manually start qemu with
different versions of virglrender (as in git versions) and the host
OpenGL, and logs test results from inside the guests. 

The guest should not do anything based on this information, for that
there are the caps, and the question is whether it is actually of
interest to have this host information always available in the guest. 

> Also using smbios as side channel doesn't look that clever.  What is
> supposed to happen on archs without smbios?
It was the simplest way to inject information into the guest without
changing too much code, and yes, I didn't think about the absence of
smbios, because I only considered it as a nice to have debug feature. 

> I think it would be better to add a VIRTIO_GPU_CMD_HOST_INFO command.
If this feature is indeed of interest then I'll happily look into how 
to implement this in qemu. To ask about this on the qemu list would
have been my next step anyway. The command line tool is only the fourth
of these patches and a quick fix for what I needed right now.

best, 
Gert