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docs: document using passt backend with <interface type='vhostuser'>

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Almost everything is already there (in the section for using passt
with type='user'), so we just need to point to that from the
type='vhostuser' section (and vice versa), and add a bit of glue.

Also updated a few related details that have changed (e.g. default
model type for vhostuser is now 'virtio', and source type/mode are now
optional), and changed "vhost-user interface" to "vhost-user
connection" because the interface is a virtio interface, and
vhost-user is being used to connect that interface to the outside.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This commit is contained in:
Laine Stump 2025-02-14 23:35:56 -05:00
parent a47a89a9d3
commit 96fd17a99b
1 changed files with 62 additions and 11 deletions
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docs/formatdomain.rst
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@ -5148,6 +5148,15 @@ destined for the host toward the guest instead), and a socket between
passt and QEMU forwards that traffic on to the guest (and back out,
of course).
*(:since:`Since 11.1.0 (QEMU and KVM only)` you may prefer to use the
passt backend with the more efficient and performant type='vhostuser'
rather than type='user'. All the options related to passt in the
paragraphs below here also apply when using the passt backend with
type='vhostuser'; any other details specific to vhostuser are
described* `here
<formatdomain.html#vhost-user-connection-with-passt-backend>`__.)
Similar to SLIRP, passt has an internal DHCP server that provides a
requesting guest with one ipv4 and one ipv6 address. There are default
values for both of these, or you can use the ``<ip>`` element
@ -5840,7 +5849,7 @@ following attributes are available for the ``virtio`` NIC driver:
The optional ``queues`` attribute controls the number of queues to be used
for either `Multiqueue
virtio-net <https://www.linux-kvm.org/page/Multiqueue>`__ or vhost-user (See
`vhost-user interface`_) network interfaces. Use of multiple packet
`vhost-user connection`_) network interfaces. Use of multiple packet
processing queues requires the interface having the
``<model type='virtio'/>`` element. Each queue will potentially be handled by
a different processor, resulting in much higher throughput.
@ -6285,8 +6294,8 @@ similarly named elements used to configure the guest side of the interface
(described above).
vhost-user interface
^^^^^^^^^^^^^^^^^^^^
vhost-user connection
^^^^^^^^^^^^^^^^^^^^^
:since:`Since 1.2.7` the vhost-user enables the communication between a QEMU
virtual machine and other userspace process using the Virtio transport protocol.
@ -6313,16 +6322,58 @@ plane is based on shared memory.
</devices>
...
The ``<source>`` element has to be specified along with the type of char device.
Currently, only type='unix' is supported, where the path (the directory path of
the socket) and mode attributes are required. Both ``mode='server'`` and
``mode='client'`` are supported. vhost-user requires the virtio model type, thus
the ``<model>`` element is mandatory. :since:`Since 4.1.0` the element has an
optional child element ``reconnect`` which configures reconnect timeout if the
connection is lost. It has two attributes ``enabled`` (which accepts ``yes`` and
``no``) and ``timeout`` which specifies the amount of seconds after which
The ``<source>`` element has to be specified along with the type of
char device. Currently, only type='unix' is supported, where the path
(the directory path of the socket) and mode attributes are
required. Both ``mode='server'`` and ``mode='client'`` are
supported. (:since:`Since 11.1.0` the default source type for
vhostuser interfaces is 'unix' and default mode is 'client', so those
two attributes are now optional).
The vhost-user protocol only works with the virtio guest driver, so
the ``<model>`` element ``type`` attribute is mandatory (:since:`Since
11.1.0` the default model type for vhostuser interfaces is now
'virtio' so ``<model>`` is no longer mandatory). :since:`Since 4.1.0`
the ``<source>`` element has an optional child element ``reconnect``
which configures reconnect timeout if the connection is lost. It has
two attributes ``enabled`` (which accepts ``yes`` and ``no``) and
``timeout`` which specifies the amount of seconds after which
hypervisor tries to reconnect.
vhost-user connection with passt backend
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
:since:`Since 11.1.0 (QEMU and KVM only)` passt can be used as the
other end of the vhost-user connection. This is a compelling
alternative, because passt provides all of its network connectivity
without requiring any elevated privileges or capabilities, and
vhost-user uses shared memory to make this unprivileged connection
very high performance as well. You can set a type='vhostuser'
interface to use passt as the backend by adding ``<backend
type='passt'/>``. When passt is the backend, only a single driver
queue is supported, and the ``<source>`` path/type/mode are all
implied to be "matching the passt process" so **must not** be
specified. All of the passt options `described here
<formatdomain.html#userspace-connection-using-passt>`__, are also
supported for ``type='vhostuser'`` with the passt backend, e.g.
setting guest-side IP addresses with ``<ip>`` and port forwarding with
``<portForward``.
::
...
<devices>
<interface type='vhostuser'>
<backend type='passt'/>
<mac address='52:54:00:3b:83:1a'/>
<source dev='enp1s0'/>
<ip address='10.30.0.5 prefix='24'/>
</interface>
</devices>
...
Traffic filtering with NWFilter
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^