[Qemu-devel] [PATCH v3 13/15] blockjob: add pause points

[Stefan Hajnoczi <stefanha@redhat.com>]

Block jobs are coroutines that usually perform I/O but sometimes also
sleep or yield.  Currently only sleeping or yielded block jobs can be
paused.  This means jobs that do not sleep or yield (using
block_job_yield()) are unaffected by block_job_pause().

Add block_job_pause_point() so that block jobs can mark quiescent points
that are suitable for pausing.  This solves the problem that is can take
a block job a long time to pause if it is performing a long series of
I/O operations.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 blockjob.c               |  7 +++++++
 include/block/blockjob.h | 12 ++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index 463bccf..b810d73 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -247,6 +247,13 @@ void block_job_complete(BlockJob *job, Error **errp)
     job->driver->complete(job, errp);
 }
 
+void block_job_pause_point(BlockJob *job)
+{
+    if (block_job_is_paused(job)) {
+        block_job_yield(job);
+    }
+}
+
 void block_job_pause(BlockJob *job)
 {
     job->pause_count++;
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 00ac418..f83a4f0 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -299,6 +299,18 @@ bool block_job_is_cancelled(BlockJob *job);
 BlockJobInfo *block_job_query(BlockJob *job);
 
 /**
+ * block_job_pause_point:
+ * @job: The job that is ready to pause.
+ *
+ * Pause now if block_job_pause() has been called.  Block jobs that perform
+ * lots of I/O must call this between requests so that the job can be paused.
+ *
+ * There must be no I/O in flight when this function is called.  There must be
+ * no I/O or event loop activity until after this function returns.
+ */
+void coroutine_fn block_job_pause_point(BlockJob *job);
+
+/**
  * block_job_pause:
  * @job: The job to be paused.
  *
-- 
2.5.5