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

[Laine Stump]

On 08/07/2012 01:53 PM, Nishank Trivedi (nistrive) wrote:
> 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.

Yes, I believe you are correct that virNetDevSetOnline is being called
with the wrong device name (I could be wrong though - is there maybe
some odd rule that the PF must be UP before the VFs will be up? In case
case, we certainly shouldn't be setting the PF to IFF_DOWN). But in the
case of PCI passthrough, does it even need to be called at all?

Cc'ing Roopa in case she missed this in all the other traffic.