On Wed, 2020-10-07 at 13:17 -0600, Alex Williamson wrote: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=' http://libvirt.org/schemas/domain/qemu/1.0'> ... <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.I am aware of it, but I never managed to get virt-manager to accept arbitary command line arguments,
That should work with no problems, as long as you know where to put it.
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:
1) change the very top line of XML that currently says
<domain type='kvm'>
to
<domain xmlns:qemu="http://libvirt.org/schemas/domain/qemu/1.0" type="kvm">
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:
<hostdev mode="subsystem" type="pci" managed="no">
<source>
<address domain="0x0000" bus="0x05" slot="0x00"
function="0x0"/>
</source>
<alias name="ua-video"/>
<address type="pci" domain="0x0000" bus="0x05" slot="0x00"
function="0x0" multifunction="on"/>
</hostdev>
3) down at the bottom of the XML, just above the
"</domain>" line, add this:
<qemu:commandline>
<qemu:arg value="-set"/>
<qemu:arg value="device.ua-video.x-vga=on"/>
</qemu:commandline>
Once you've made these 3 small changes, click on the "Apply"
button.
but never persisted in trying to get it to work since it felt hackier than patching libvirt to accept the parameter.
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.
