qapi: Add ImageInfoSpecific type

Add a new type ImageInfoSpecific as a union for image format specific
information in ImageInfo.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

qapi-schema.json

@@ -209,6 +209,18 @@
             'date-sec': 'int', 'date-nsec': 'int',
             'vm-clock-sec': 'int', 'vm-clock-nsec': 'int' } }
 
+##
+# @ImageInfoSpecific:
+#
+# A discriminated record of image format specific information structures.
+#
+# Since: 1.7
+##
+
+{ 'union': 'ImageInfoSpecific',
+  'data': {
+  } }
+
 ##
 # @ImageInfo:
 #
@@ -238,6 +250,9 @@
 #
 # @backing-image: #optional info of the backing image (since 1.6)
 #
+# @format-specific: #optional structure supplying additional format-specific
+# information (since 1.7)
+#
 # Since: 1.3
 #
 ##
@@ -248,7 +263,8 @@
            '*cluster-size': 'int', '*encrypted': 'bool',
            '*backing-filename': 'str', '*full-backing-filename': 'str',
            '*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
-           '*backing-image': 'ImageInfo' } }
+           '*backing-image': 'ImageInfo',
+           '*format-specific': 'ImageInfoSpecific' } }
 
 ##
 # @ImageCheck: