block/create: Make x-blockdev-create a job

This changes the x-blockdev-create QMP command so that it doesn't block
the monitor and the main loop any more, but starts a background job that
performs the image creation.

The basic job as implemented here is all that is necessary to make image
creation asynchronous and to provide a QMP interface that can be marked
stable, but it still lacks a few features that jobs usually provide: The
job will ignore pause commands and it doesn't publish more than very
basic progress yet (total-progress is 1 and current-progress advances
from 0 to 1 when the driver callbacks returns). These features can be
added later without breaking compatibility.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>

qapi/block-core.json

@@ -4013,14 +4013,18 @@
 ##
 # @x-blockdev-create:
 #
-# Create an image format on a given node.
-# TODO Replace with something asynchronous (block job?)
+# Starts a job to create an image format on a given node. The job is
+# automatically finalized, but a manual job-dismiss is required.
 #
-# Since: 2.12
+# @job-id:          Identifier for the newly created job.
+#
+# @options:         Options for the image creation.
+#
+# Since: 3.0
 ##
 { 'command': 'x-blockdev-create',
-  'data': 'BlockdevCreateOptions',
-  'boxed': true }
+  'data': { 'job-id': 'str',
+            'options': 'BlockdevCreateOptions' } }
 
 ##
 # @blockdev-open-tray:

qapi/job.json

@@ -17,10 +17,12 @@
 #
 # @backup: drive backup job type, see "drive-backup"
 #
+# @create: image creation job type, see "x-blockdev-create" (since 3.0)
+#
 # Since: 1.7
 ##
 { 'enum': 'JobType',
-  'data': ['commit', 'stream', 'mirror', 'backup'] }
+  'data': ['commit', 'stream', 'mirror', 'backup', 'create'] }
 
 ##
 # @JobStatus: