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diff --git a/Documentation/networking/net_failover.rst b/Documentation/networking/net_failover.rst new file mode 100644 index 0000000000000..70ca2f5800c43 --- /dev/null +++ b/Documentation/networking/net_failover.rst @@ -0,0 +1,116 @@ +.. 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. + + <interface type='network'> + <mac address='52:54:00:00:12:53'/> + <source network='enp66s0f0_br'/> + <target dev='tap01'/> + <model type='virtio'/> + <driver name='vhost' queues='4'/> + <link state='down'/> + <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/> + </interface> + <interface type='hostdev' managed='yes'> + <mac address='52:54:00:00:12:53'/> + <source> + <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/> + </source> + <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/> + </interface> + +Booting a VM with the above configuration will result in the following 3 +netdevs created in the VM. + +4: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> 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: <BROADCAST,MULTICAST,UP,LOWER_UP> 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: <BROADCAST,MULTICAST,UP,LOWER_UP> 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 +<interface type='hostdev' managed='yes'> + <mac address='52:54:00:00:12:53'/> + <source> + <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/> + </source> + <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/> +</interface> + +# 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 |