1.. SPDX-License-Identifier: GPL-2.0
  2
  3============
  4NET_FAILOVER
  5============
  6
  7Overview
  8========
  9
 10The net_failover driver provides an automated failover mechanism via APIs
 11to create and destroy a failover master netdev and mananges a primary and
 12standby slave netdevs that get registered via the generic failover
 13infrastructrure.
 14
 15The failover netdev acts a master device and controls 2 slave devices. The
 16original paravirtual interface is registered as 'standby' slave netdev and
 17a passthru/vf device with the same MAC gets registered as 'primary' slave
 18netdev. Both 'standby' and 'failover' netdevs are associated with the same
 19'pci' device. The user accesses the network interface via 'failover' netdev.
 20The 'failover' netdev chooses 'primary' netdev as default for transmits when
 21it is available with link up and running.
 22
 23This can be used by paravirtual drivers to enable an alternate low latency
 24datapath. It also enables hypervisor controlled live migration of a VM with
 25direct attached VF by failing over to the paravirtual datapath when the VF
 26is unplugged.
 27
 28virtio-net accelerated datapath: STANDBY mode
 29=============================================
 30
 31net_failover enables hypervisor controlled accelerated datapath to virtio-net
 32enabled VMs in a transparent manner with no/minimal guest userspace chanages.
 33
 34To support this, the hypervisor needs to enable VIRTIO_NET_F_STANDBY
 35feature on the virtio-net interface and assign the same MAC address to both
 36virtio-net and VF interfaces.
 37
 38Here is an example XML snippet that shows such configuration.
 39::
 40
 41  <interface type='network'>
 42    <mac address='52:54:00:00:12:53'/>
 43    <source network='enp66s0f0_br'/>
 44    <target dev='tap01'/>
 45    <model type='virtio'/>
 46    <driver name='vhost' queues='4'/>
 47    <link state='down'/>
 48    <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
 49  </interface>
 50  <interface type='hostdev' managed='yes'>
 51    <mac address='52:54:00:00:12:53'/>
 52    <source>
 53      <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
 54    </source>
 55    <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
 56  </interface>
 57
 58Booting a VM with the above configuration will result in the following 3
 59netdevs created in the VM.
 60::
 61
 62  4: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
 63      link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
 64      inet 192.168.12.53/24 brd 192.168.12.255 scope global dynamic ens10
 65         valid_lft 42482sec preferred_lft 42482sec
 66      inet6 fe80::97d8:db2:8c10:b6d6/64 scope link
 67         valid_lft forever preferred_lft forever
 68  5: ens10nsby: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master ens10 state UP group default qlen 1000
 69      link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
 70  7: ens11: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ens10 state UP group default qlen 1000
 71      link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
 72
 73ens10 is the 'failover' master netdev, ens10nsby and ens11 are the slave
 74'standby' and 'primary' netdevs respectively.
 75
 76Live Migration of a VM with SR-IOV VF & virtio-net in STANDBY mode
 77==================================================================
 78
 79net_failover also enables hypervisor controlled live migration to be supported
 80with VMs that have direct attached SR-IOV VF devices by automatic failover to
 81the paravirtual datapath when the VF is unplugged.
 82
 83Here is a sample script that shows the steps to initiate live migration on
 84the source hypervisor.
 85::
 86
 87  # cat vf_xml
 88  <interface type='hostdev' managed='yes'>
 89    <mac address='52:54:00:00:12:53'/>
 90    <source>
 91      <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
 92    </source>
 93    <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
 94  </interface>
 95
 96  # Source Hypervisor
 97  #!/bin/bash
 98
 99  DOMAIN=fedora27-tap01
100  PF=enp66s0f0
101  VF_NUM=5
102  TAP_IF=tap01
103  VF_XML=
104
105  MAC=52:54:00:00:12:53
106  ZERO_MAC=00:00:00:00:00:00
107
108  virsh domif-setlink $DOMAIN $TAP_IF up
109  bridge fdb del $MAC dev $PF master
110  virsh detach-device $DOMAIN $VF_XML
111  ip link set $PF vf $VF_NUM mac $ZERO_MAC
112
113  virsh migrate --live $DOMAIN qemu+ssh://$REMOTE_HOST/system
114
115  # Destination Hypervisor
116  #!/bin/bash
117
118  virsh attach-device $DOMAIN $VF_XML
119  virsh domif-setlink $DOMAIN $TAP_IF down