Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when available

On Tue, Mar 13, 2018 at 05:28:07PM -0700, Samudrala, Sridhar wrote:

quoted

I am not sure if it's a good idea to leave the
virtio_bypass around if running into failure: the guest is not
migratable as the VF doesn't have a backup path,

Are you talking about a failure when registering backup netdev?  This should not
happen, but i guess we can improve error handling in such scenario.

A nice way to do this would be to clear the backup feature bit.

quoted

And perhaps the worse
part is that, it now has two interfaces with identical MAC address but
one of them is invalid (user cannot use the virtio interface as it has
a dampened datapath). IMHO the virtio_bypass and its lower netdev
should be destroyed at all when it fails to bind the VF, and
technically, there should be some way to propogate the failure status
to the hypervisor/backend, indicating that the VM is not migratable
because of guest software errors (maybe by clearing out the backup
feature from the guest virtio driver so host can see/learn it).

In BACKUP mode, user can only use the upper virtio_bypass netdev and that will
always be there. Any failure to enslave VF netdev is not fatal, but i will see
if we can improve the error handling of failure to enslave backup netdev.
Also, i don't think the BACKUP feature bit is negotiable with the host.

Thanks
Sridhar

All bits are negotiable.  It's up to the host whether to support
a device with this bit clear, or to fail negotiation.

-- 
MST