block/mirror: change the semantic of 'force' of block-job-cancel

When doing drive mirror to a low speed shared storage, if there was heavy
BLK IO write workload in VM after the 'ready' event, drive mirror block job
can't be canceled immediately, it would keep running until the heavy BLK IO
workload stopped in the VM.

Libvirt depends on the current block-job-cancel semantics, which is that
when used without a flag after the 'ready' event, the command blocks
until data is in sync.  However, these semantics are awkward in other
situations, for example, people may use drive mirror for realtime
backups while still wanting to use block live migration.  Libvirt cannot
start a block live migration while another drive mirror is in progress,
but the user would rather abandon the backup attempt as broken and
proceed with the live migration than be stuck waiting for the current
drive mirror backup to finish.

The drive-mirror command already includes a 'force' flag, which libvirt
does not use, although it documented the flag as only being useful to
quit a job which is paused.  However, since quitting a paused job has
the same effect as abandoning a backup in a non-paused job (namely, the
destination file is not in sync, and the command completes immediately),
we can just improve the documentation to make the force flag obviously
useful.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jeff Cody <jcody@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Reported-by: Huaitong Han <huanhuaitong@didichuxing.com>
Signed-off-by: Huaitong Han <huanhuaitong@didichuxing.com>
Signed-off-by: Liang Li <liliangleo@didichuxing.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 978274e..fc645da 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -63,6 +63,12 @@ typedef struct BlockJob {
     bool cancelled;
 
     /**
+     * Set to true if the job should abort immediately without waiting
+     * for data to be in sync.
+     */
+    bool force;
+
+    /**
      * Counter for pause request. If non-zero, the block job is either paused,
      * or if busy == true will pause itself as soon as possible.
      */
@@ -230,10 +236,11 @@ void block_job_start(BlockJob *job);
 /**
  * block_job_cancel:
  * @job: The job to be canceled.
+ * @force: Quit a job without waiting for data to be in sync.
  *
  * Asynchronously cancel the specified job.
  */
-void block_job_cancel(BlockJob *job);
+void block_job_cancel(BlockJob *job, bool force);
 
 /**
  * block_job_complete:
@@ -307,11 +314,12 @@ void block_job_user_resume(BlockJob *job, Error **errp);
 /**
  * block_job_user_cancel:
  * @job: The job to be cancelled.
+ * @force: Quit a job without waiting for data to be in sync.
  *
  * Cancels the specified job, but may refuse to do so if the
  * operation isn't currently meaningful.
  */
-void block_job_user_cancel(BlockJob *job, Error **errp);
+void block_job_user_cancel(BlockJob *job, bool force, Error **errp);
 
 /**
  * block_job_cancel_sync: