.. SPDX-License-Identifier: GPL-2.0 ============ NET_FAILOVER ============ Overview ======== The net_failover driver provides an automated failover mechanism via APIs to create and destroy a failover master netdev and mananges a primary and standby slave netdevs that get registered via the generic failover infrastructrure. The failover netdev acts a master device and controls 2 slave devices. The original paravirtual interface is registered as 'standby' slave netdev and a passthru/vf device with the same MAC gets registered as 'primary' slave netdev. Both 'standby' and 'failover' netdevs are associated with the same 'pci' device. The user accesses the network interface via 'failover' netdev. The 'failover' netdev chooses 'primary' netdev as default for transmits when it is available with link up and running. This can be used by paravirtual drivers to enable an alternate low latency datapath. It also enables hypervisor controlled live migration of a VM with direct attached VF by failing over to the paravirtual datapath when the VF is unplugged. virtio-net accelerated datapath: STANDBY mode ============================================= net_failover enables hypervisor controlled accelerated datapath to virtio-net enabled VMs in a transparent manner with no/minimal guest userspace chanages. To support this, the hypervisor needs to enable VIRTIO_NET_F_STANDBY feature on the virtio-net interface and assign the same MAC address to both virtio-net and VF interfaces. Here is an example XML snippet that shows such configuration.
Booting a VM with the above configuration will result in the following 3 netdevs created in the VM. 4: ens10: mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff inet 192.168.12.53/24 brd 192.168.12.255 scope global dynamic ens10 valid_lft 42482sec preferred_lft 42482sec inet6 fe80::97d8:db2:8c10:b6d6/64 scope link valid_lft forever preferred_lft forever 5: ens10nsby: mtu 1500 qdisc fq_codel master ens10 state UP group default qlen 1000 link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff 7: ens11: mtu 1500 qdisc mq master ens10 state UP group default qlen 1000 link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff ens10 is the 'failover' master netdev, ens10nsby and ens11 are the slave 'standby' and 'primary' netdevs respectively. Live Migration of a VM with SR-IOV VF & virtio-net in STANDBY mode ================================================================== net_failover also enables hypervisor controlled live migration to be supported with VMs that have direct attached SR-IOV VF devices by automatic failover to the paravirtual datapath when the VF is unplugged. Here is a sample script that shows the steps to initiate live migration on the source hypervisor. # cat vf_xml
# Source Hypervisor #!/bin/bash DOMAIN=fedora27-tap01 PF=enp66s0f0 VF_NUM=5 TAP_IF=tap01 VF_XML= MAC=52:54:00:00:12:53 ZERO_MAC=00:00:00:00:00:00 virsh domif-setlink $DOMAIN $TAP_IF up bridge fdb del $MAC dev $PF master virsh detach-device $DOMAIN $VF_XML ip link set $PF vf $VF_NUM mac $ZERO_MAC virsh migrate --live $DOMAIN qemu+ssh://$REMOTE_HOST/system # Destination Hypervisor #!/bin/bash virsh attach-device $DOMAIN $VF_XML virsh domif-setlink $DOMAIN $TAP_IF down