diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/devel/kconfig.rst | 2 | ||||
| -rw-r--r-- | docs/interop/vhost-user.rst | 17 |
2 files changed, 18 insertions, 1 deletions
diff --git a/docs/devel/kconfig.rst b/docs/devel/kconfig.rst index d6f8eb0977..b7bca44704 100644 --- a/docs/devel/kconfig.rst +++ b/docs/devel/kconfig.rst @@ -267,7 +267,7 @@ the default configuration by uncommenting lines in the first group, or commenting out lines in the second group. It is also possible to run QEMU's configure script with the -``--with-default-devices`` option. When this is done, everything defaults +``--without-default-devices`` option. When this is done, everything defaults to ``n`` unless it is ``select``ed or explicitly switched on in the ``.mak`` files. In other words, ``default`` and ``imply`` directives are disabled. When QEMU is built with this option, the user will probably diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst index 5750668aba..7827b710aa 100644 --- a/docs/interop/vhost-user.rst +++ b/docs/interop/vhost-user.rst @@ -324,6 +324,15 @@ must support changing some configuration aspects on the fly. Multiple queue support ---------------------- +Many devices have a fixed number of virtqueues. In this case the master +already knows the number of available virtqueues without communicating with the +slave. + +Some devices do not have a fixed number of virtqueues. Instead the maximum +number of virtqueues is chosen by the slave. The number can depend on host +resource availability or slave implementation details. Such devices are called +multiple queue devices. + Multiple queue support allows the slave to advertise the maximum number of queues. This is treated as a protocol extension, hence the slave has to implement protocol features first. The multiple queues feature is supported @@ -339,6 +348,14 @@ queue in the sent message to identify a specified queue. The master enables queues by sending message ``VHOST_USER_SET_VRING_ENABLE``. vhost-user-net has historically automatically enabled the first queue pair. +Slaves should always implement the ``VHOST_USER_PROTOCOL_F_MQ`` protocol +feature, even for devices with a fixed number of virtqueues, since it is simple +to implement and offers a degree of introspection. + +Masters must not rely on the ``VHOST_USER_PROTOCOL_F_MQ`` protocol feature for +devices with a fixed number of virtqueues. Only true multiqueue devices +require this protocol feature. + Migration --------- |