block: use BDS ref for block jobs

Block jobs used drive_get_ref(drive_get_by_blockdev(bs)) to avoid BDS
being deleted. Now we have BDS reference count, and block jobs don't
care about dinfo, so replace them to get cleaner code. It is also the
safe way when BDS has no drive info.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

blockdev.c

@@ -234,32 +234,32 @@ void drive_get_ref(DriveInfo *dinfo)
 
 typedef struct {
     QEMUBH *bh;
-    DriveInfo *dinfo;
-} DrivePutRefBH;
+    BlockDriverState *bs;
+} BDRVPutRefBH;
 
-static void drive_put_ref_bh(void *opaque)
+static void bdrv_put_ref_bh(void *opaque)
 {
-    DrivePutRefBH *s = opaque;
+    BDRVPutRefBH *s = opaque;
 
-    drive_put_ref(s->dinfo);
+    bdrv_unref(s->bs);
     qemu_bh_delete(s->bh);
     g_free(s);
 }
 
 /*
- * Release a drive reference in a BH
+ * Release a BDS reference in a BH
  *
- * It is not possible to use drive_put_ref() from a callback function when the
- * callers still need the drive.  In such cases we schedule a BH to release the
- * reference.
+ * 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 drive_put_ref_bh_schedule(DriveInfo *dinfo)
+static void bdrv_put_ref_bh_schedule(BlockDriverState *bs)
 {
-    DrivePutRefBH *s;
+    BDRVPutRefBH *s;
 
-    s = g_new(DrivePutRefBH, 1);
-    s->bh = qemu_bh_new(drive_put_ref_bh, s);
-    s->dinfo = dinfo;
+    s = g_new(BDRVPutRefBH, 1);
+    s->bh = qemu_bh_new(bdrv_put_ref_bh, s);
+    s->bs = bs;
     qemu_bh_schedule(s->bh);
 }
 
@@ -1436,7 +1436,7 @@ static void block_job_cb(void *opaque, int ret)
     }
     qobject_decref(obj);
 
-    drive_put_ref_bh_schedule(drive_get_by_blockdev(bs));
+    bdrv_put_ref_bh_schedule(bs);
 }
 
 void qmp_block_stream(const char *device, bool has_base,
@@ -1473,11 +1473,6 @@ void qmp_block_stream(const char *device, bool has_base,
         return;
     }
 
-    /* Grab a reference so hotplug does not delete the BlockDriverState from
-     * underneath us.
-     */
-    drive_get_ref(drive_get_by_blockdev(bs));
-
     trace_qmp_block_stream(bs, bs->job);
 }
 
@@ -1534,10 +1529,6 @@ void qmp_block_commit(const char *device,
         error_propagate(errp, local_err);
         return;
     }
-    /* Grab a reference so hotplug does not delete the BlockDriverState from
-     * underneath us.
-     */
-    drive_get_ref(drive_get_by_blockdev(bs));
 }
 
 void qmp_drive_backup(const char *device, const char *target,
@@ -1650,11 +1641,6 @@ void qmp_drive_backup(const char *device, const char *target,
         error_propagate(errp, local_err);
         return;
     }
-
-    /* Grab a reference so hotplug does not delete the BlockDriverState from
-     * underneath us.
-     */
-    drive_get_ref(drive_get_by_blockdev(bs));
 }
 
 #define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
@@ -1791,11 +1777,6 @@ void qmp_drive_mirror(const char *device, const char *target,
         error_propagate(errp, local_err);
         return;
     }
-
-    /* Grab a reference so hotplug does not delete the BlockDriverState from
-     * underneath us.
-     */
-    drive_get_ref(drive_get_by_blockdev(bs));
 }
 
 static BlockJob *find_block_job(const char *device)

blockjob.c

@@ -45,6 +45,7 @@ void *block_job_create(const BlockJobType *job_type, BlockDriverState *bs,
         error_set(errp, QERR_DEVICE_IN_USE, bdrv_get_device_name(bs));
         return NULL;
     }
+    bdrv_ref(bs);
     bdrv_set_in_use(bs, 1);
 
     job = g_malloc0(job_type->instance_size);