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<div class="moz-cite-prefix">On 10/7/20 5:44 PM, Steven Newbury
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:a2617efc09baaa3b005f05f25e24b47da514e6c4.camel@snewbury.org.uk">
<pre class="moz-quote-pre" wrap="">On Wed, 2020-10-07 at 13:17 -0600, Alex Williamson wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Are you aware that you can add arbitrary options to devices using the
<qemu:commandline> support in libvirt? For example:
<domain type='kvm' xmlns:qemu='
<a class="moz-txt-link-freetext" href="http://libvirt.org/schemas/domain/qemu/1.0">http://libvirt.org/schemas/domain/qemu/1.0</a>'>
...
<devices>
...
<hostdev mode='subsystem' type='pci' managed='yes'>
<source>
<address domain='0x0000' bus='0x01' slot='0x00'
function='0x0'/>
</source>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00'
function='0x0'/>
<alias name='ua-geforce8800'/>
</hostdev>
...
</devices>
<qemu:commandline>
<qemu:arg value='-set'/>
<qemu:arg value='device.ua-geforce8800.x-vga=on'/>
</qemu:commandline>
</domain>
This is generally how users make use of unsupportable or
not-yet-supported QEMU features while still using libvirt to manage
the
VM.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">I am aware of it, but I never managed to get virt-manager to accept
arbitary command line arguments,</pre>
</blockquote>
<p><br>
</p>
<p>That should work with no problems, as long as you know where to
put it.</p>
<p><br>
</p>
<p>If you go into the configuration for a guest (either during guest
creation by clicking on "Customize configuration before install",
or after creation by double clicking on the guest name then
clicking on the "light bulb" icon at the upper left), click on
"Overview" in the list on the left, then click on the "XML" tab
above the right-hand side of the window (the default tab is
"Details"), then you should be presented with the full XML for the
guest. You'll need to do three things:</p>
<p><br>
</p>
<p>1) change the very top line of XML that currently says</p>
<p><br>
</p>
<p> <domain type='kvm'></p>
<p><br>
</p>
<p>to</p>
<p><br>
</p>
<p> <domain
xmlns:qemu=<a class="moz-txt-link-rfc2396E" href="http://libvirt.org/schemas/domain/qemu/1.0">"http://libvirt.org/schemas/domain/qemu/1.0"</a>
type="kvm"></p>
<p><br>
</p>
<p>2) In the middle of the XML, where you will find the
<hostdev> element for your assigned GPU (similar to this
example), add the line "<alias name="ua-video"/> as shown
here:<br>
</p>
<p> <hostdev mode="subsystem" type="pci" managed="no"><br>
<source><br>
<address domain="0x0000" bus="0x05" slot="0x00"
function="0x0"/><br>
</source><br>
<alias name="ua-video"/><br>
<address type="pci" domain="0x0000" bus="0x05" slot="0x00"
function="0x0" multifunction="on"/><br>
</hostdev><br>
<br>
</p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source></p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source></p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source></p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source></p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source></p>
<p> </p>
<address>
<address type="pci"> </address>
</address>
<p><source> </p>
<p><source></p>
<p>3) down at the bottom of the XML, just above the
"</domain>" line, add this:<br>
</p>
<p> <qemu:commandline><br>
<qemu:arg value="-set"/><br>
<qemu:arg value="device.ua-video.x-vga=on"/><br>
</qemu:commandline><br>
<br>
</p>
<p>Once you've made these 3 small changes, click on the "Apply"
button.<br>
<br>
</p>
<blockquote type="cite"
cite="mid:a2617efc09baaa3b005f05f25e24b47da514e6c4.camel@snewbury.org.uk">
<pre class="moz-quote-pre" wrap=""> but never persisted in trying to get
it to work since it felt hackier than patching libvirt to accept the
parameter.</pre>
</blockquote>
<p><br>
</p>
<p>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).</p>
<p><br>
</p>
<p>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.</p>
<p><br>
</p>
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