blockjob: introduce block-job-change QMP command

which will allow changing job-type-specific options after job
creation.

In the JobVerbTable, the same allow bits as for set-speed are used,
because set-speed can be considered an existing change command.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20231031135431.393137-2-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qapi/block-core.json

@@ -3044,6 +3044,32 @@
 { 'command': 'block-job-finalize', 'data': { 'id': 'str' },
   'allow-preconfig': true }
 
+##
+# @BlockJobChangeOptions:
+#
+# Block job options that can be changed after job creation.
+#
+# @id: The job identifier
+#
+# @type: The job type
+#
+# Since 8.2
+##
+{ 'union': 'BlockJobChangeOptions',
+  'base': { 'id': 'str', 'type': 'JobType' },
+  'discriminator': 'type',
+  'data': {} }
+
+##
+# @block-job-change:
+#
+# Change the block job's options.
+#
+# Since: 8.2
+##
+{ 'command': 'block-job-change',
+  'data': 'BlockJobChangeOptions', 'boxed': true }
+
 ##
 # @BlockdevDiscardOptions:
 #

qapi/job.json

@@ -105,11 +105,13 @@
 #
 # @finalize: see @job-finalize
 #
+# @change: see @block-job-change (since 8.2)
+#
 # Since: 2.12
 ##
 { 'enum': 'JobVerb',
   'data': ['cancel', 'pause', 'resume', 'set-speed', 'complete', 'dismiss',
-           'finalize' ] }
+           'finalize', 'change' ] }
 
 ##
 # @JOB_STATUS_CHANGE: