On 09/01/2016 04:05 AM, Moshe Levi wrote:
Hi,
In OpenStack we have a port type macvtap.
Mavtap port is just a tap device connected to VF.
In Libvirt the guest xml look like
<interface type='direct'>
<mac address='fa:16:3e:b1:06:4e'/>
<source dev='p1p6' mode='passthrough'/>
<target dev='macvtap1'/>
<model type='virtio'/>
<driver name='vhost'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
In the hypervisor we can see that the mac of the VF which is fa:16:3e:f3:9b:e8 - is set by OpenStack see [1]
9: ens3f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ovs-system state UP mode DEFAULT group default qlen 1000
link/ether 7c:fe:90:29:24:4e brd ff:ff:ff:ff:ff:ff
vf 0 MAC 00:00:00:00:00:00, spoof checking off, link-state disable
vf 1 MAC 00:00:00:00:00:00, spoof checking off, link-state disable
vf 2 MAC fa:16:3e:f3:9b:e8, vlan 48, spoof checking on, link-state enable
vf 3 MAC fa:16:3e:f6:02:c8, vlan 48, spoof checking on, link-state enable
41: ens3f4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether fa:16:3e:f6:02:c8 brd ff:ff:ff:ff:ff:ff
42: macvtap0@ens3f4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 500
link/ether fa:16:3e:f6:02:c8, brd ff:ff:ff:ff:ff:ff
The netdevice of the VF which is ens3f4 has also the same mac. This mac is set when using Libvirt 1.2.2 (Ubuntu 14.04),
But when we tested with new Libvirt versions >= 1.2.17 (Fedora 23/Ubuntu 16.04) the mac netdevice of the VF (ens3f4) is not set.
This change in Libvirt breaks the guest from getting DHCP in OpenStack.
Do you know why the behavior change in newer releases?
The MAC address is now set with a netlink command to set the VFINFO of
the particular VF# of the PF. This change was made in response to a bug
report stating that once the MAC address had been set for a hostdev
assignment of a VF (in which case this method is required), it was no
longer possible to set the MAC address for macvtap passthrough (the VF
driver would complain "MAC has been administratively set", on Intel
igbvf at least). Unfortunately I recently found that when you set the
MAC address in this manner, it doesn't take effect on the actual device
- it's only saved in memory to be applied the *next time* the host
driver is rebound to the VF.
Since I don't see a reasonably efficient way to get this to work, I need
to make a patch to revert to the old behavior, and we'll then just have
to tell people "If you do hostdev device assignment of VFs, then you
can't later re-use the same device for macvtap passthrough mode".
(actually, I *think* an alternative would be to unbind/rebind the host
driver to the VF after setting the VF MAC address, but that seems a bit
disruptive/extreme to work around a problem that is probably only seen
in QE labs, but not in the real world (realistically, production systems
likely use either hostdev or macvtap, and don't switch back and forth
between them).
A question - I notice you have the vlan set for the VF. Does *that*
properly take effect? (it's set in the same manner as the MAC address,
via a netlink command to set the VFINFO)
We have a WIP patch in OpenStack for setting also the mac for the netdevice of the VF [2]. Just wanted to know that this is the correct approach.
[1] - https://github.com/openstack/nova/blob/master/nova/virt/libvirt/vif.py#L616-L621
[2] - https://review.openstack.org/#/c/364121/
Thanks,
Moshe Levi
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