[Qemu-devel] [PATCH v4 3/5] blockjob: add AioContext attached callback

[Stefan Hajnoczi <stefanha@redhat.com>]

Block jobs that use additional BDSes or event loop resources need a
callback to get their affairs in order when the AioContext is switched.

Simple block jobs don't need an attach callback, they automatically work
thanks to the generic attach/detach notifiers that this patch adds.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 blockjob.c               | 38 ++++++++++++++++++++++++++++++++++++++
 include/block/blockjob.h |  7 +++++++
 2 files changed, 45 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index 1a383d1..a5ce982 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -60,6 +60,38 @@ BlockJob *block_job_next(BlockJob *job)
     return QLIST_NEXT(job, job_list);
 }
 
+static void block_job_attached_aio_context(AioContext *new_context,
+                                           void *opaque)
+{
+    BlockJob *job = opaque;
+
+    if (job->driver->attached_aio_context) {
+        job->driver->attached_aio_context(job, new_context);
+    }
+
+    block_job_resume(job);
+}
+
+static void block_job_detach_aio_context(void *opaque)
+{
+    BlockJob *job = opaque;
+
+    /* In case the job terminates during aio_poll()... */
+    block_job_ref(job);
+
+    block_job_pause(job);
+
+    if (!job->paused) {
+        /* If job is !job->busy this kicks it into the next pause point. */
+        block_job_enter(job);
+    }
+    while (!job->paused && !job->completed) {
+        aio_poll(blk_get_aio_context(job->blk), true);
+    }
+
+    block_job_unref(job);
+}
+
 void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
                        int64_t speed, BlockCompletionFunc *cb,
                        void *opaque, Error **errp)
@@ -92,6 +124,9 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
 
     QLIST_INSERT_HEAD(&block_jobs, job, job_list);
 
+    blk_add_aio_context_notifier(blk, block_job_attached_aio_context,
+                                 block_job_detach_aio_context, job);
+
     /* Only set speed when necessary to avoid NotSupported error */
     if (speed != 0) {
         Error *local_err = NULL;
@@ -117,6 +152,9 @@ void block_job_unref(BlockJob *job)
         BlockDriverState *bs = blk_bs(job->blk);
         bs->job = NULL;
         bdrv_op_unblock_all(bs, job->blocker);
+        blk_remove_aio_context_notifier(job->blk,
+                                        block_job_attached_aio_context,
+                                        block_job_detach_aio_context, job);
         blk_unref(job->blk);
         error_free(job->blocker);
         g_free(job->id);
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 154c48b..98550bc 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -84,6 +84,13 @@ typedef struct BlockJobDriver {
      * should be restarted from this callback.
      */
     void (*resume)(BlockJob *job);
+
+    /*
+     * If the callback is not NULL, it will be invoked before the job is
+     * resumed in a new AioContext.  This is the place to move any resources
+     * besides job->blk to the new AioContext.
+     */
+    void (*attached_aio_context)(BlockJob *job, AioContext *new_context);
 } BlockJobDriver;
 
 /**
-- 
2.5.5