[libvirt] RFC: setting mac address on network devices being assigned to a guest via PCI passthrough (<hostdev>)

[Laine Stump]

On 01/30/2012 08:16 PM, Roopa Prabhu wrote:
> Laine, I haven't gone through your whole email yet. Was just curious about
> one quick thing,
>
> For sriov VF's, are we expecting that a net device (eth interface) be
> present on the host if its being used as a hostdev ?.


Either should be possible. If the VF is bound to a net dev, it can be 
specified either with dev='ethxx' or using its pci address, and will be 
unbound before assigning to the guest. If it's not bound to a net dev, 
then a pci address must be used to describe it in the config.


>   If yes, then libvirt
> will need to do an unbind of the driver on the VF before assigning it to the
> VM. Which today it does not do (correct me if I am wrong).


That may have been the case in the past, but with libvirt-0.9.9 (the 
first version that I've tested with sriov and PCI passthrough - I'm a 
newbie to both), the net driver is unbound prior to assigning to the 
guest, and when the the device is detached from the guest, the net 
driver is once again bound to the device.


> Which is still
> ok. Just wanted to call that out.
> Plus ideally it would be nice to not have an expectation that a vf netdevice
> be present on the host. Because for sriov vf's, it would mean that the vf
> driver has to be loaded on the host. Which is really not required for vfs
> because mac and port profile can be set via the pf with the vf index as
> argument.

Right. For sriov VFs, I intend that the MAC address will always be set 
via the PF. I hadn't previously thought through the details for 
non-sriov devices, but your event sequence list below made me realize 
that, at least for non-sriov, the MAC address and virtual port setup 
will need to be done *before* unbinding the driver (my intent, for sriov 
at least, was that this would happen *after* unbinding the driver). I 
guess that will take some experimentation.

Anyway, at the moment I'm slogging around in the data structures.

>
> Basically,
> For non-sriov network devices on host,
>      - find netdevice
>      - set mac on netdevice
>      - If required set port profile on the netdevice
>      - unbind netdevice driver
>      - assign net pci device to guest
>
>
> For sriov vf network devices on host,
>      - find pf netdevice
>      - set mac for vf via the pf netdevice
>      - If required set port profile on the vf via the pf netdevice
>      - unbind vf driver if its loaded on the vf /* not mandatory */
>      - assign vf pci device to guest
>
> Thanks!
> -Roopa
>
>