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qemu/docs/virtio-net-failover.rst

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docs: fix rst syntax errors in unbuilt docs The .rst files outside docs/{devel,interop,specs} aren't built yet and therefore a few syntax errors have slipped through. Fix them. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20191111094411.427174-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-11-11 12:44:11 +03:00
======================================
net/virtio: add failover support This patch adds support to handle failover device pairs of a virtio-net device and a (vfio-)pci device, where the virtio-net acts as the standby device and the (vfio-)pci device as the primary. The general idea is that we have a pair of devices, a (vfio-)pci and a emulated (virtio-net) device. Before migration the vfio device is unplugged and data flows to the emulated device, on the target side another (vfio-)pci device is plugged in to take over the data-path. In the guest the net_failover module will pair net devices with the same MAC address. To achieve this we need: 1. Provide a callback function for the should_be_hidden DeviceListener. It is called when the primary device is plugged in. Evaluate the QOpt passed in to check if it is the matching primary device. It returns if the device should be hidden or not. When it should be hidden it stores the device options in the VirtioNet struct and the device is added once the VIRTIO_NET_F_STANDBY feature is negotiated during virtio feature negotiation. If the virtio-net devices are not realized at the time the (vfio-)pci devices are realized, we need to connect the devices later. This way we make sure primary and standby devices can be specified in any order. 2. Register a callback for migration status notifier. When called it will unplug its primary device before the migration happens. 3. Register a callback for the migration code that checks if a device needs to be unplugged from the guest. Signed-off-by: Jens Freimann <jfreimann@redhat.com> Message-Id: <20191029114905.6856-11-jfreimann@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-10-29 14:49:04 +03:00
QEMU virtio-net standby (net_failover)
docs: fix rst syntax errors in unbuilt docs The .rst files outside docs/{devel,interop,specs} aren't built yet and therefore a few syntax errors have slipped through. Fix them. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20191111094411.427174-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-11-11 12:44:11 +03:00
======================================
net/virtio: add failover support This patch adds support to handle failover device pairs of a virtio-net device and a (vfio-)pci device, where the virtio-net acts as the standby device and the (vfio-)pci device as the primary. The general idea is that we have a pair of devices, a (vfio-)pci and a emulated (virtio-net) device. Before migration the vfio device is unplugged and data flows to the emulated device, on the target side another (vfio-)pci device is plugged in to take over the data-path. In the guest the net_failover module will pair net devices with the same MAC address. To achieve this we need: 1. Provide a callback function for the should_be_hidden DeviceListener. It is called when the primary device is plugged in. Evaluate the QOpt passed in to check if it is the matching primary device. It returns if the device should be hidden or not. When it should be hidden it stores the device options in the VirtioNet struct and the device is added once the VIRTIO_NET_F_STANDBY feature is negotiated during virtio feature negotiation. If the virtio-net devices are not realized at the time the (vfio-)pci devices are realized, we need to connect the devices later. This way we make sure primary and standby devices can be specified in any order. 2. Register a callback for migration status notifier. When called it will unplug its primary device before the migration happens. 3. Register a callback for the migration code that checks if a device needs to be unplugged from the guest. Signed-off-by: Jens Freimann <jfreimann@redhat.com> Message-Id: <20191029114905.6856-11-jfreimann@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-10-29 14:49:04 +03:00
This document explains the setup and usage of virtio-net standby feature which
is used to create a net_failover pair of devices.
The general idea is that we have a pair of devices, a (vfio-)pci and a
virtio-net device. Before migration the vfio device is unplugged and data flows
through the virtio-net device, on the target side another vfio-pci device is
plugged in to take over the data-path. In the guest the net_failover kernel
module will pair net devices with the same MAC address.
The two devices are called primary and standby device. The fast hardware based
networking device is called the primary device and the virtio-net device is the
standby device.
Restrictions
------------
Currently only PCIe devices are allowed as primary devices, this restriction
can be lifted in the future with enhanced QEMU support. Also, only networking
devices are allowed as primary device. The user needs to ensure that primary
and standby devices are not plugged into the same PCIe slot.
Usecase
-------
Virtio-net standby allows easy migration while using a passed-through fast
networking device by falling back to a virtio-net device for the duration of
the migration. It is like a simple version of a bond, the difference is that it
requires no configuration in the guest. When a guest is live-migrated to
another host QEMU will unplug the primary device via the PCIe based hotplug
handler and traffic will go through the virtio-net device. On the target
system the primary device will be automatically plugged back and the
net_failover module registers it again as the primary device.
Usage
-----
The primary device can be hotplugged or be part of the startup configuration
-device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc, \
bus=root2,failover=on
With the parameter failover=on the VIRTIO_NET_F_STANDBY feature will be enabled.
-device vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,failover_pair_id=net1
failover_pair_id references the id of the virtio-net standby device. This
is only for pairing the devices within QEMU. The guest kernel module
net_failover will match devices with identical MAC addresses.
Hotplug
-------
Both primary and standby device can be hotplugged via the QEMU monitor. Note
that if the virtio-net device is plugged first a warning will be issued that it
couldn't find the primary device.
Migration
---------
A new migration state wait-unplug was added for this feature. If failover primary
devices are present in the configuration, migration will go into this state.
It will wait until the device unplug is completed in the guest and then move into
active state. On the target system the primary devices will be automatically hotplugged
when the feature bit was negotiated for the virtio-net standby device.
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