Re: [Libvirt] Attach qemu commands to an running xml domain
On 3/30/21 11:35 AM, Waleed Musa wrote:
Hi all,
I see in libvirt you are supporting attach/detach devices to existing
xml domain using *attachDeviceFlags *and *detachDeviceFlags *APIs.
Now we are adding some qemu command to the xml domain related to some
interfaces using alias names before starting the VM, but we will face an
issue with hot plug such devices, so I have two question here:
1. Is it applicable to set the alias names for interfaces because I saw
it's ignored when I add it to xml domain before starting the VM?
2. Is there a way or API to attach qemu commands to running domain as
you are doing in attaching the device using *attachDeviceFlags?*
*Example of my xml*
*<domain type='kvm' id='5'
xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
*
* <devices>
*
<interface type='vhostuser'>
<mac address='fa:16:3e:ac:12:4c'/>
<source type='unix'
path='/var/lib/vhost_sockets/sockbbb6bbe9-eb5' mode='server'/>
<target dev='tapbbb6bbe9-eb'/>
<model type='virtio'/>
<driver queues='4' rx_queue_size='512'
tx_queue_size='512'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03'
function='0x0'/>
</interface>
* </devices>
*
* <qemu:commandline>*
<qemu:arg value='-set'/>
<qemu:arg value='device.net0.page-per-vq=on'/>
<qemu:arg value='-set'/>
<qemu:arg value='device.net0.host_mtu=8942'/>
* </qemu:commandline>*
*</domain>*
Is this perhaps related to the following bug?
"interface type='vhostuser' libvirtError: Cannot set interface MTU"
https://bugzilla.redhat.com/show_bug.cgi?id=1940559
Are you trying to work around it? I am discussing with Moshe how libvirt
can help, but honestly, I don't like the solution I proposed.
Long story short, the interface is in different container (among with
OVS bridge) and thus when we query ovs-vsctl it connects to the system
one and doesn't find that interface. What I proposed was to allow
specifying path to ovs db.socket but this would need to be done o per
domain basis.
What I particularly don't like about this solution is that while it may
fix this one use case, it opens the gate for whole lot of other
requests. For instance, consider if other interfaces of other types live
in different network namespace. "Hey, I want to use eth0 from that
namespace, but run QEMU in another one".
Also, we don't really like exposing paths in libvirt XML unless necessary.
Michal