[libvirt] PF interface brought down if guest using a VF in hostdev mode under 802.1Qbh

[Nishank Trivedi (nistrive)]

Hi,

In 802.1Qbh case where exists a SR-IOV capable network device, if any of
the virtual functions of this device is used in hostdev mode for the
guest, port-profile disassociate will also cause physical function
interface to go down. This appears to be a bug, but wanted to find if this
was done intentionally for some reasons.

To be more specific, if a network device supports SRIOV and its VF is
being used in pci passthrough mode, when the guest is shutdown or
destroyed following happens -

qemuProcessStop
\_ qemuDomainReAttachHostdevDevices(hostdevs)
 \_ qemuDomainHostdevNetConfigRestore(hostdev)
  \_ virNetDevPortProfileDisassociate(linkdev)
   \_ virNetDevSetOnline(linkdev, false)

In above, qemuDomainHostdevNetConfigRestore() finds out the PF for
provided hostdev (which is VF) and passes it to
virNetDevPortProfileDisassociate() as linkdev. Later, linkdev gets passed
to virNetDevSetOnline() where the interface is brought down by clearing
IFF_UP flag. 

However, in macvtap emulation mode,
virNetDevMacVLanDeleteWithVPortProfile() passes VF as linkdev (and -1 as
vf) to virNetDevPortProfileDisassociate(), hence, not affecting PF at all.

Bringing down a PF, when only VF is being brought down is not expected
behavior (unless, I'm missing something here). A way to get around it
would be to check if there exists vf (>=0) in
virNetDevPortProfileDisassociate(), and if so, it should only pass the
interface name of this VF rather than PF itself to virNetDevSetOnline().
If it sounds reasonable, I'll send out a fix.

Thanks,
Nishank