[PATCH] Support x-vga=on for PCI host passthrough devices

Laine Stump laine at redhat.com
Thu Oct 8 17:17:49 UTC 2020

On 10/8/20 4:54 AM, Steven Newbury wrote:
> On Wed, 2020-10-07 at 21:45 -0400, Laine Stump wrote:
>> It is *definitely* less hacky to use <qemu:commandline> than to carry
>> your own local patch on top of the libvirt source, which would force
>> you to always build your own libvirt binaries, and rebase your patch
>> every time upstream libvirt changed code that touched the same place.
>> Although <qemu:commandline> isn't "Supported" (Capital "S" - in the
>> sense that a vendor providing paid technical support for a system
>> using libvirt won't officially commit themselves to solving any
>> problem you may have associated with use of <qemu:commandline>, and
>> the options you provide there *could* disappear from qemu), it is
>> "supported" (small "s" - in the sense that libvirt has no plans to
>> remove <qemu:commandline>, and it is used by other people so if it
>> becomes broken it will surely get fixed).
>> Using <qemu:commandline> will take 10 minutes of your time right now,
>> and then you'll never have to think about it ever again (until/unless
>> QEMU removes the x-vga option). Using your own custom build of
>> libvirt that carries a locally written patch will continue to be a
>> burden every time you upgrade libvirt until the end of time.
> Thanks for the detailed instructions, I had missed the alias part
> before, I don't know if that was where I was going wrong? 

Nah, that would just lead to an error when you started the guest.

> The
> <qemu::commandline> part would just disappear when I hit apply.

The most likely reason for that would be a) if you left out step (1), or 
b) if you put <qemu:commandline> after </domain>, or maybe put it inside 
some other element (e.g. <devices>).

> The original patch only took me 10mins at most, yeah it shows, but
> worked straight away.  I've been running Gentoo unstable for the last
> 20 years, patch rebasing isn't really a problem! :-)  I'm very used to
> creating patches for new features and bug fixes as I need to, it's part
> of my usual update process.  I must have written thousands over the
> years.  I've been trying to make a bit of effort to get some pushed
> upstream, rather than having them sit in an overlay or
> "portage/patches".
> It is taking some time and effort to get the validation working, but I
> don't think it's a waste of time.  I'm getting better familarised with
> the code which isn't a bad thing, and might allow me to make more
> appropriate contributions in the future.

Now *that* is a worthwhile reason! :-)

> Maybe I'll try fixing the
> "isapc" machine type?! ;-)

Hmm. Trying to think of why you would need that (other than just the 
standard "because it's there"), and coming up empty. I *think* even 
MSDOS will boot on an i440fx guest...

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