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119 lines
4.3 KiB
ReStructuredText
119 lines
4.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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============
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NET_FAILOVER
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============
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Overview
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========
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The net_failover driver provides an automated failover mechanism via APIs
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to create and destroy a failover master netdev and mananges a primary and
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standby slave netdevs that get registered via the generic failover
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infrastructrure.
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The failover netdev acts a master device and controls 2 slave devices. The
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original paravirtual interface is registered as 'standby' slave netdev and
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a passthru/vf device with the same MAC gets registered as 'primary' slave
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netdev. Both 'standby' and 'failover' netdevs are associated with the same
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'pci' device. The user accesses the network interface via 'failover' netdev.
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The 'failover' netdev chooses 'primary' netdev as default for transmits when
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it is available with link up and running.
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This can be used by paravirtual drivers to enable an alternate low latency
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datapath. It also enables hypervisor controlled live migration of a VM with
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direct attached VF by failing over to the paravirtual datapath when the VF
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is unplugged.
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virtio-net accelerated datapath: STANDBY mode
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=============================================
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net_failover enables hypervisor controlled accelerated datapath to virtio-net
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enabled VMs in a transparent manner with no/minimal guest userspace chanages.
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To support this, the hypervisor needs to enable VIRTIO_NET_F_STANDBY
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feature on the virtio-net interface and assign the same MAC address to both
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virtio-net and VF interfaces.
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Here is an example XML snippet that shows such configuration.
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::
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<interface type='network'>
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<mac address='52:54:00:00:12:53'/>
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<source network='enp66s0f0_br'/>
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<target dev='tap01'/>
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<model type='virtio'/>
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<driver name='vhost' queues='4'/>
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<link state='down'/>
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<address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
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</interface>
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<interface type='hostdev' managed='yes'>
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<mac address='52:54:00:00:12:53'/>
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<source>
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<address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
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</source>
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<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
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</interface>
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Booting a VM with the above configuration will result in the following 3
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netdevs created in the VM.
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::
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4: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
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link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
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inet 192.168.12.53/24 brd 192.168.12.255 scope global dynamic ens10
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valid_lft 42482sec preferred_lft 42482sec
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inet6 fe80::97d8:db2:8c10:b6d6/64 scope link
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valid_lft forever preferred_lft forever
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5: ens10nsby: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master ens10 state UP group default qlen 1000
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link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
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7: ens11: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ens10 state UP group default qlen 1000
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link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
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ens10 is the 'failover' master netdev, ens10nsby and ens11 are the slave
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'standby' and 'primary' netdevs respectively.
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Live Migration of a VM with SR-IOV VF & virtio-net in STANDBY mode
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==================================================================
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net_failover also enables hypervisor controlled live migration to be supported
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with VMs that have direct attached SR-IOV VF devices by automatic failover to
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the paravirtual datapath when the VF is unplugged.
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Here is a sample script that shows the steps to initiate live migration on
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the source hypervisor.
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::
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# cat vf_xml
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<interface type='hostdev' managed='yes'>
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<mac address='52:54:00:00:12:53'/>
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<source>
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<address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
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</source>
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<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
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</interface>
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# Source Hypervisor
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#!/bin/bash
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DOMAIN=fedora27-tap01
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PF=enp66s0f0
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VF_NUM=5
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TAP_IF=tap01
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VF_XML=
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MAC=52:54:00:00:12:53
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ZERO_MAC=00:00:00:00:00:00
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virsh domif-setlink $DOMAIN $TAP_IF up
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bridge fdb del $MAC dev $PF master
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virsh detach-device $DOMAIN $VF_XML
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ip link set $PF vf $VF_NUM mac $ZERO_MAC
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virsh migrate --live $DOMAIN qemu+ssh://$REMOTE_HOST/system
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# Destination Hypervisor
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#!/bin/bash
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virsh attach-device $DOMAIN $VF_XML
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virsh domif-setlink $DOMAIN $TAP_IF down
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