block: introduce BLOCK_JOB_READY event

Even for jobs that need to be manually completed, management may want
to take care itself of the completion, not requiring the user to issue
a command to terminate the job.  In this case we want to avoid that
they poll us continuously, waiting for completion to become available.
Thus, add a new event that signals the phase switch and the availability
of the block-job-complete command.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

QMP/qmp-events.txt

@@ -118,6 +118,24 @@ Example:
               "action": "stop" },
     "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
 
+BLOCK_JOB_READY
+---------------
+
+Emitted when a block job is ready to complete.
+
+Data:
+
+- "device": device name (json-string)
+
+Example:
+
+{ "event": "BLOCK_JOB_READY",
+    "data": { "device": "ide0-hd1" },
+    "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
+
+Note: The "ready to complete" status is always reset by a BLOCK_JOB_ERROR
+event.
+
 DEVICE_TRAY_MOVED
 -----------------
 

blockdev.c

@@ -1056,20 +1056,6 @@ void qmp_block_resize(const char *device, int64_t size, Error **errp)
     }
 }
 
-static QObject *qobject_from_block_job(BlockJob *job)
-{
-    return qobject_from_jsonf("{ 'type': %s,"
-                              "'device': %s,"
-                              "'len': %" PRId64 ","
-                              "'offset': %" PRId64 ","
-                              "'speed': %" PRId64 " }",
-                              job->job_type->job_type,
-                              bdrv_get_device_name(job->bs),
-                              job->len,
-                              job->offset,
-                              job->speed);
-}
-
 static void block_job_cb(void *opaque, int ret)
 {
     BlockDriverState *bs = opaque;

blockjob.c

@@ -225,6 +225,27 @@ static void block_job_iostatus_set_err(BlockJob *job, int error)
 }
 
 
+QObject *qobject_from_block_job(BlockJob *job)
+{
+    return qobject_from_jsonf("{ 'type': %s,"
+                              "'device': %s,"
+                              "'len': %" PRId64 ","
+                              "'offset': %" PRId64 ","
+                              "'speed': %" PRId64 " }",
+                              job->job_type->job_type,
+                              bdrv_get_device_name(job->bs),
+                              job->len,
+                              job->offset,
+                              job->speed);
+}
+
+void block_job_ready(BlockJob *job)
+{
+    QObject *data = qobject_from_block_job(job);
+    monitor_protocol_event(QEVENT_BLOCK_JOB_READY, data);
+    qobject_decref(data);
+}
+
 BlockErrorAction block_job_error_action(BlockJob *job, BlockDriverState *bs,
                                         BlockdevOnError on_err,
                                         int is_read, int error)

blockjob.h

@@ -210,6 +210,22 @@ void block_job_pause(BlockJob *job);
  */
 void block_job_resume(BlockJob *job);
 
+/**
+ * qobject_from_block_job:
+ * @job: The job whose information is requested.
+ *
+ * Return a QDict corresponding to @job's query-block-jobs entry.
+ */
+QObject *qobject_from_block_job(BlockJob *job);
+
+/**
+ * block_job_ready:
+ * @job: The job which is now ready to complete.
+ *
+ * Send a BLOCK_JOB_READY event for the specified job.
+ */
+void block_job_ready(BlockJob *job);
+
 /**
  * block_job_is_paused:
  * @job: The job being queried.

monitor.c

@@ -451,6 +451,7 @@ static const char *monitor_event_names[] = {
     [QEVENT_BLOCK_JOB_COMPLETED] = "BLOCK_JOB_COMPLETED",
     [QEVENT_BLOCK_JOB_CANCELLED] = "BLOCK_JOB_CANCELLED",
     [QEVENT_BLOCK_JOB_ERROR] = "BLOCK_JOB_ERROR",
+    [QEVENT_BLOCK_JOB_READY] = "BLOCK_JOB_READY",
     [QEVENT_DEVICE_TRAY_MOVED] = "DEVICE_TRAY_MOVED",
     [QEVENT_SUSPEND] = "SUSPEND",
     [QEVENT_SUSPEND_DISK] = "SUSPEND_DISK",

monitor.h

@@ -39,6 +39,7 @@ typedef enum MonitorEvent {
     QEVENT_BLOCK_JOB_COMPLETED,
     QEVENT_BLOCK_JOB_CANCELLED,
     QEVENT_BLOCK_JOB_ERROR,
+    QEVENT_BLOCK_JOB_READY,
     QEVENT_DEVICE_TRAY_MOVED,
     QEVENT_SUSPEND,
     QEVENT_SUSPEND_DISK,

qapi-schema.json

@@ -2037,7 +2037,8 @@
 #
 # Manually trigger completion of an active background block operation.  This
 # is supported for drive mirroring, where it also switches the device to
-# write to the target path only.
+# write to the target path only.  The ability to complete is signaled with
+# a BLOCK_JOB_READY event.
 #
 # This command completes an active background block operation synchronously.
 # The ordering of this command's return with the BLOCK_JOB_COMPLETED event