Documentation/networking/net_failover.rst

   1 .. SPDX-License-Identifier: GPL-2.0
   2
   3 ============
   4 NET_FAILOVER
   5 ============
   6
   7 Overview
   8 ========
   9
  10 The net_failover driver provides an automated failover mechanism via APIs
  11 to create and destroy a failover master netdev and mananges a primary and
  12 standby slave netdevs that get registered via the generic failover
  13 infrastructrure.
  14
  15 The failover netdev acts a master device and controls 2 slave devices. The
  16 original paravirtual interface is registered as 'standby' slave netdev and
  17 a passthru/vf device with the same MAC gets registered as 'primary' slave
  18 netdev. Both 'standby' and 'failover' netdevs are associated with the same
  19 'pci' device. The user accesses the network interface via 'failover' netdev.
  20 The 'failover' netdev chooses 'primary' netdev as default for transmits when
  21 it is available with link up and running.
  22
  23 This can be used by paravirtual drivers to enable an alternate low latency
  24 datapath. It also enables hypervisor controlled live migration of a VM with
  25 direct attached VF by failing over to the paravirtual datapath when the VF
  26 is unplugged.
  27
  28 virtio-net accelerated datapath: STANDBY mode
  29 =============================================
  30
  31 net_failover enables hypervisor controlled accelerated datapath to virtio-net
  32 enabled VMs in a transparent manner with no/minimal guest userspace chanages.
  33
  34 To support this, the hypervisor needs to enable VIRTIO_NET_F_STANDBY
  35 feature on the virtio-net interface and assign the same MAC address to both
  36 virtio-net and VF interfaces.
  37
  38 Here 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
  58 Booting a VM with the above configuration will result in the following 3
  59 netdevs 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
  73 ens10 is the 'failover' master netdev, ens10nsby and ens11 are the slave
  74 'standby' and 'primary' netdevs respectively.
  75
  76 Live Migration of a VM with SR-IOV VF & virtio-net in STANDBY mode
  77 ==================================================================
  78
  79 net_failover also enables hypervisor controlled live migration to be supported
  80 with VMs that have direct attached SR-IOV VF devices by automatic failover to
  81 the paravirtual datapath when the VF is unplugged.
  82
  83 Here is a sample script that shows the steps to initiate live migration on
  84 the 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