vhost-user: add multiple queue support

This patch is initially based a patch from Nikolay Nikolaev.

This patch adds vhost-user multiple queue support, by creating a nc
and vhost_net pair for each queue.

Qemu exits if find that the backend can't support the number of requested
queues (by providing queues=# option). The max number is queried by a
new message, VHOST_USER_GET_QUEUE_NUM, and is sent only when protocol
feature VHOST_USER_PROTOCOL_F_MQ is present first.

The max queue check is done at vhost-user initiation stage. We initiate
one queue first, which, in the meantime, also gets the max_queues the
backend supports.

In older version, it was reported that some messages are sent more times
than necessary. Here we came an agreement with Michael that we could
categorize vhost user messages to 2 types: non-vring specific messages,
which should be sent only once, and vring specific messages, which should
be sent per queue.

Here I introduced a helper function vhost_user_one_time_request(), which
lists following messages as non-vring specific messages:

        VHOST_USER_SET_OWNER
        VHOST_USER_RESET_DEVICE
        VHOST_USER_SET_MEM_TABLE
        VHOST_USER_GET_QUEUE_NUM

For above messages, we simply ignore them when they are not sent the first
time.

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Tested-by: Marcel Apfelbaum <marcel@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index 7e147b8aac..328404ca18 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1990,13 +1990,14 @@ The hubport netdev lets you connect a NIC to a QEMU "vlan" instead of a single
 netdev.  @code{-net} and @code{-device} with parameter @option{vlan} create the
 required hub automatically.
 
-@item -netdev vhost-user,chardev=@var{id}[,vhostforce=on|off]
+@item -netdev vhost-user,chardev=@var{id}[,vhostforce=on|off][,queues=n]
 
 Establish a vhost-user netdev, backed by a chardev @var{id}. The chardev should
 be a unix domain socket backed one. The vhost-user uses a specifically defined
 protocol to pass vhost ioctl replacement messages to an application on the other
 end of the socket. On non-MSIX guests, the feature can be forced with
-@var{vhostforce}.
+@var{vhostforce}. Use 'queues=@var{n}' to specify the number of queues to
+be created for multiqueue vhost-user.
 
 Example:
 @example