blockjob: Introduce reference count and fix reference to job->bs

Add reference count to block job, meanwhile move the ownership of the
reference to job->bs from the caller (which is released in two
completion callbacks) to the block job itself. It is necessary for
block_job_complete_sync to work, because block job shouldn't live longer
than its bs, as asserted in bdrv_delete.

Now block_job_complete_sync can be simplified.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1446765200-3054-6-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/mirror.c

@@ -742,7 +742,7 @@ static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,
     s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity, NULL, errp);
     if (!s->dirty_bitmap) {
         g_free(s->replaces);
-        block_job_release(bs);
+        block_job_unref(&s->common);
         return;
     }
 

blockdev.c

@@ -283,32 +283,6 @@ typedef struct {
     BlockDriverState *bs;
 } BDRVPutRefBH;
 
-static void bdrv_put_ref_bh(void *opaque)
-{
-    BDRVPutRefBH *s = opaque;
-
-    bdrv_unref(s->bs);
-    qemu_bh_delete(s->bh);
-    g_free(s);
-}
-
-/*
- * Release a BDS reference in a BH
- *
- * It is not safe to use bdrv_unref() from a callback function when the callers
- * still need the BlockDriverState.  In such cases we schedule a BH to release
- * the reference.
- */
-static void bdrv_put_ref_bh_schedule(BlockDriverState *bs)
-{
-    BDRVPutRefBH *s;
-
-    s = g_new(BDRVPutRefBH, 1);
-    s->bh = qemu_bh_new(bdrv_put_ref_bh, s);
-    s->bs = bs;
-    qemu_bh_schedule(s->bh);
-}
-
 static int parse_block_error_action(const char *buf, bool is_read, Error **errp)
 {
     if (!strcmp(buf, "ignore")) {
@@ -2741,8 +2715,6 @@ static void block_job_cb(void *opaque, int ret)
     } else {
         block_job_event_completed(bs->job, msg);
     }
-
-    bdrv_put_ref_bh_schedule(bs);
 }
 
 void qmp_block_stream(const char *device,

blockjob.c

@@ -60,6 +60,7 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
     job->cb            = cb;
     job->opaque        = opaque;
     job->busy          = true;
+    job->refcnt        = 1;
     bs->job = job;
 
     /* Only set speed when necessary to avoid NotSupported error */
@@ -68,23 +69,29 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
 
         block_job_set_speed(job, speed, &local_err);
         if (local_err) {
-            block_job_release(bs);
+            block_job_unref(job);
             error_propagate(errp, local_err);
             return NULL;
         }
     }
     return job;
 }
 
-void block_job_release(BlockDriverState *bs)
+void block_job_ref(BlockJob *job)
 {
-    BlockJob *job = bs->job;
+    ++job->refcnt;
+}
 
-    bs->job = NULL;
-    bdrv_op_unblock_all(bs, job->blocker);
-    error_free(job->blocker);
-    g_free(job->id);
-    g_free(job);
+void block_job_unref(BlockJob *job)
+{
+    if (--job->refcnt == 0) {
+        job->bs->job = NULL;
+        bdrv_op_unblock_all(job->bs, job->blocker);
+        bdrv_unref(job->bs);
+        error_free(job->blocker);
+        g_free(job->id);
+        g_free(job);
+    }
 }
 
 void block_job_completed(BlockJob *job, int ret)
@@ -93,7 +100,7 @@ void block_job_completed(BlockJob *job, int ret)
 
     assert(bs->job == job);
     job->cb(job->opaque, ret);
-    block_job_release(bs);
+    block_job_unref(job);
 }
 
 void block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)

include/block/blockjob.h

@@ -130,6 +130,9 @@ struct BlockJob {
 
     /** The opaque value that is passed to the completion function.  */
     void *opaque;
+
+    /** Reference count of the block job */
+    int refcnt;
 };
 
 /**
@@ -174,12 +177,21 @@ void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns);
 void block_job_yield(BlockJob *job);
 
 /**
- * block_job_release:
+ * block_job_ref:
+ * @bs: The block device.
+ *
+ * Grab a reference to the block job. Should be paired with block_job_unref.
+ */
+void block_job_ref(BlockJob *job);
+
+/**
+ * block_job_unref:
  * @bs: The block device.
  *
- * Release job resources when an error occurred or job completed.
+ * Release reference to the block job and release resources if it is the last
+ * reference.
  */
-void block_job_release(BlockDriverState *bs);
+void block_job_unref(BlockJob *job);
 
 /**
  * block_job_completed:

qemu-img.c

@@ -645,9 +645,6 @@ static void common_block_job_cb(void *opaque, int ret)
     if (ret < 0) {
         error_setg_errno(cbi->errp, -ret, "Block job failed");
     }
-
-    /* Drop this block job's reference */
-    bdrv_unref(cbi->bs);
 }
 
 static void run_block_job(BlockJob *job, Error **errp)