Implement backend program convention command for vhost-user-blk

This patch is to add standard commands defined in docs/interop/vhost-user.rst
For vhost-user-* program

Signed-off-by: Micky Yun Chan (michiboo) <chanmickyyun@gmail.com>
Message-Id: <20191209015331.5455-1-chanmickyyun@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

docs/interop/vhost-user.json

@@ -54,6 +54,37 @@
   ]
 }
 
+##
+# @VHostUserBackendBlockFeature:
+#
+# List of vhost user "block" features.
+#
+# @read-only: The --read-only command line option is supported.
+# @blk-file: The --blk-file command line option is supported.
+#
+# Since: 5.0
+##
+{
+  'enum': 'VHostUserBackendBlockFeature',
+  'data': [ 'read-only', 'blk-file' ]
+}
+
+##
+# @VHostUserBackendCapabilitiesBlock:
+#
+# Capabilities reported by vhost user "block" backends
+#
+# @features: list of supported features.
+#
+# Since: 5.0
+##
+{
+  'struct': 'VHostUserBackendCapabilitiesBlock',
+  'data': {
+    'features': [ 'VHostUserBackendBlockFeature' ]
+  }
+}
+
 ##
 # @VHostUserBackendInputFeature:
 #

docs/interop/vhost-user.rst

@@ -1376,3 +1376,20 @@ Command line options:
   Enable virgl rendering support.
 
   (optional)
+
+vhost-user-blk
+--------------
+
+Command line options:
+
+--blk-file=PATH
+
+  Specify block device or file path.
+
+  (optional)
+
+--read-only
+
+  Enable read-only.
+
+  (optional)