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

On 3/31/21 1:36 PM, Daniel P. Berrangé wrote: > 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. Because then you'd override the path for system wide OVS. I mean, by default the socket is under /var/run/openvswitch/db.sock and if you have another OVS running inside a container you can expose it under /prefix/var/run/openvswitch/db.sock. ovs-vsctl allows this by --db=$path argument.