1 Commits

Author	SHA1	Message	Date
Laine Stump	eb9f6cc4b3	qemu: support interface <teaming> functionality ... The QEMU driver uses the <teaming type='persistent|transient' persistent='blah'/> element to setup a "failover" pair of devices - the persistent device must be a virtio emulated NIC, with the only extra configuration being the addition of ",failover=on" to the device commandline, and the transient device must be a hostdev NIC (<interface type='hostdev'> or <interface type='network'> with a network that is a pool of SRIOV VFs) where the extra configuration is the addition of ",failover_pair_id=$aliasOfVirtio" to the device commandline. These new options are supported in QEMU 4.2.0 and later. Extra qemu-specific validation is added to ensure that the device type/model is appropriate and that the qemu binary supports these commandline options. The result of this will be: 1) The virtio device presented to the guest will have an extra bit set in its PCI capabilities indicating that it can be used as a failover backup device. The virtio guest driver will need to be equipped to do something with this information - this is included in the Linux virtio-net driver in kernel 4.18 and above (and also backported to some older distro kernels). Unfortunately there is no way for libvirt to learn whether or not the guest driver supports failover - if it doesn't then the extra PCI capability will be ignored and the guest OS will just see two independent devices. (NB: the current virtio guest driver also requires that the MAC addresses of the two NICs match in order to pair them into a bond). 2) When a migration is requested, QEMu will automatically unplug the transient/hostdev NIC from the guest on the source host before starting migration, and automatically re-plug a similar device after restarting the guest CPUs on the destination host. While the transient NIC is unplugged, all network traffic will go through the persistent/virtio device, but when the hostdev NIC is plugged in, it will get all the traffic. This means that in normal circumstances the guest gets the performance advantage of vfio-assigned "real hardware" networking, but it can still be migrated with the only downside being a performance penalty (due to using an emulated NIC) during the migration. Signed-off-by: Laine Stump <laine@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>	2020-01-29 15:33:29 -05:00