qsd: document vduse-blk exports

Document vduse-blk exports in qemu-storage-daemon --help and the
qemu-storage-daemon(1) man page.

Based-on: <20220523084611.91-1-xieyongji@bytedance.com>
Cc: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220525121947.859820-1-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

docs/tools/qemu-storage-daemon.rst

@@ -77,6 +77,7 @@ Standard options:
   --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=unix,addr.path=<socket-path>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
   --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=fd,addr.str=<fd>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
   --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off][,allow-other=on|off|auto]
+  --export [type=]vduse-blk,id=<id>,node-name=<node-name>[,writable=on|off][,num-queues=<num-queues>][,queue-size=<queue-size>][,logical-block-size=<block-size>]
 
   is a block export definition. ``node-name`` is the block node that should be
   exported. ``writable`` determines whether or not the export allows write
@@ -110,6 +111,26 @@ Standard options:
   ``allow-other`` to auto (the default) will try enabling this option, and on
   error fall back to disabling it.
 
+  The ``vduse-blk`` export type uses the ``id`` as the VDUSE device name.
+  ``num-queues`` sets the number of virtqueues (the default is 1).
+  ``queue-size`` sets the virtqueue descriptor table size (the default is 256).
+
+  The instantiated VDUSE device must then be added to the vDPA bus using the
+  vdpa(8) command from the iproute2 project::
+
+  # vdpa dev add name <id> mgmtdev vduse
+
+  The device can be removed from the vDPA bus later as follows::
+
+  # vdpa dev del <id>
+
+  For more information about attaching vDPA devices to the host with
+  virtio_vdpa.ko or attaching them to guests with vhost_vdpa.ko, see
+  https://vdpa-dev.gitlab.io/.
+
+  For more information about VDUSE, see
+  https://docs.kernel.org/userspace-api/vduse.html.
+
 .. option:: --monitor MONITORDEF
 
   is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for

storage-daemon/qemu-storage-daemon.c

@@ -121,6 +121,15 @@ static void help(void)
 "                         vhost-user-blk device over file descriptor\n"
 "\n"
 #endif /* CONFIG_VHOST_USER_BLK_SERVER */
+#ifdef CONFIG_VDUSE_BLK_EXPORT
+"  --export [type=]vduse-blk,id=<id>,node-name=<node-name>\n"
+"           [,writable=on|off][,num-queues=<num-queues>]\n"
+"           [,queue-size=<queue-size>]\n"
+"           [,logical-block-size=<logical-block-size>]\n"
+"                         export the specified block node as a vduse-blk\n"
+"                         device using the id as the VDUSE device name\n"
+"\n"
+#endif /* CONFIG_VDUSE_BLK_EXPORT */
 "  --monitor [chardev=]name[,mode=control][,pretty[=on|off]]\n"
 "                         configure a QMP monitor\n"
 "\n"