Re: [Libvirt] Attach qemu commands to an running xml domain

On Wed, Mar 31, 2021 at 01:09:32PM +0200, Michal Privoznik wrote: > 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. If it is possible to specify a ovs db.socket path in the XML, then why can't this path simply be bind mounted to the right location in the first place.