[Qemu-devel] [PATCH 3/8] block: implement reference count for BlockDriverState

[Fam Zheng <famz@redhat.com>]

Introduce bdrv_ref/bdrv_unref to manage the lifecycle of
BlockDriverState. They are unused for now but will used to replace
bdrv_delete() later.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c                   | 22 ++++++++++++++++++++++
 include/block/block.h     |  2 ++
 include/block/block_int.h |  1 +
 3 files changed, 25 insertions(+)

diff --git a/block.c b/block.c
index 6cd39fa..6f7ad7f 100644
--- a/block.c
+++ b/block.c
@@ -306,6 +306,7 @@ BlockDriverState *bdrv_new(const char *device_name)
     bdrv_iostatus_disable(bs);
     notifier_list_init(&bs->close_notifiers);
     notifier_with_return_list_init(&bs->before_write_notifiers);
+    bs->refcnt = 1;
 
     return bs;
 }
@@ -1511,6 +1512,9 @@ static void bdrv_move_feature_fields(BlockDriverState *bs_dest,
     /* dirty bitmap */
     bs_dest->dirty_bitmap       = bs_src->dirty_bitmap;
 
+    /* reference count */
+    bs_dest->refcnt             = bs_src->refcnt;
+
     /* job */
     bs_dest->in_use             = bs_src->in_use;
     bs_dest->job                = bs_src->job;
@@ -4385,6 +4389,24 @@ int64_t bdrv_get_dirty_count(BlockDriverState *bs)
     }
 }
 
+/* Get a reference to bs */
+void bdrv_ref(BlockDriverState *bs)
+{
+    bs->refcnt++;
+}
+
+/* Release a previously grabbed reference to bs.
+ * If after releasing, reference count is zero, the BlockDriverState is
+ * deleted. */
+void bdrv_unref(BlockDriverState *bs)
+{
+    assert(bs->refcnt > 0);
+    if (--bs->refcnt == 0) {
+        bdrv_close(bs);
+        bdrv_delete(bs);
+    }
+}
+
 void bdrv_set_in_use(BlockDriverState *bs, int in_use)
 {
     assert(bs->in_use != in_use);
diff --git a/include/block/block.h b/include/block/block.h
index 742fce5..b33ef62 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -356,6 +356,8 @@ int64_t bdrv_get_dirty_count(BlockDriverState *bs);
 void bdrv_enable_copy_on_read(BlockDriverState *bs);
 void bdrv_disable_copy_on_read(BlockDriverState *bs);
 
+void bdrv_ref(BlockDriverState *bs);
+void bdrv_unref(BlockDriverState *bs);
 void bdrv_set_in_use(BlockDriverState *bs, int in_use);
 int bdrv_in_use(BlockDriverState *bs);
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index c6ac871..a282d56 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -294,6 +294,7 @@ struct BlockDriverState {
     BlockDeviceIoStatus iostatus;
     char device_name[32];
     HBitmap *dirty_bitmap;
+    int refcnt;
     int in_use; /* users other than guest access, eg. block migration */
     QTAILQ_ENTRY(BlockDriverState) list;
 
-- 
1.8.3.2