block: add support for job pause/resume

Job pausing reuses the existing support for cancellable sleeps.  A pause
happens at the next sleeping point and lasts until the coroutine is
re-entered explicitly.  Cancellation was already doing a forced resume,
so implement it explicitly in terms of resume.

Paused jobs cannot be canceled without first resuming them.  This ensures
that I/O errors are never missed by management.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/blockjob.h b/blockjob.h
index f3d8d58ce3..ece5afa75b 100644
--- a/blockjob.h
+++ b/blockjob.h
@@ -70,6 +70,12 @@ struct BlockJob {
     bool cancelled;
 
     /**
+     * Set to true if the job is either paused, or will pause itself
+     * as soon as possible (if busy == true).
+     */
+    bool paused;
+
+    /**
      * Set to false by the job while it is in a quiescent state, where
      * no I/O is pending and the job has yielded on any condition
      * that is not detected by #qemu_aio_wait, such as a timer.
@@ -171,6 +177,31 @@ bool block_job_is_cancelled(BlockJob *job);
 BlockJobInfo *block_job_query(BlockJob *job);
 
 /**
+ * block_job_pause:
+ * @job: The job to be paused.
+ *
+ * Asynchronously pause the specified job.
+ */
+void block_job_pause(BlockJob *job);
+
+/**
+ * block_job_resume:
+ * @job: The job to be resumed.
+ *
+ * Resume the specified job.
+ */
+void block_job_resume(BlockJob *job);
+
+/**
+ * block_job_is_paused:
+ * @job: The job being queried.
+ *
+ * Returns whether the job is currently paused, or will pause
+ * as soon as it reaches a sleeping point.
+ */
+bool block_job_is_paused(BlockJob *job);
+
+/**
  * block_job_cancel_sync:
  * @job: The job to be canceled.
  *