block: Avoid unchecked casts for AIOCBs

Use container_of for one direction and &acb->common for the other one.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -2108,7 +2108,8 @@ typedef struct BlockDriverAIOCBSync {
 
 static void bdrv_aio_cancel_em(BlockDriverAIOCB *blockacb)
 {
-    BlockDriverAIOCBSync *acb = (BlockDriverAIOCBSync *)blockacb;
+    BlockDriverAIOCBSync *acb =
+        container_of(blockacb, BlockDriverAIOCBSync, common);
     qemu_bh_delete(acb->bh);
     acb->bh = NULL;
     qemu_aio_release(acb);

block/blkdebug.c

@@ -320,7 +320,7 @@ static void error_callback_bh(void *opaque)
 
 static void blkdebug_aio_cancel(BlockDriverAIOCB *blockacb)
 {
-    BlkdebugAIOCB *acb = (BlkdebugAIOCB*) blockacb;
+    BlkdebugAIOCB *acb = container_of(blockacb, BlkdebugAIOCB, common);
     qemu_aio_release(acb);
 }
 
@@ -347,7 +347,7 @@ static BlockDriverAIOCB *inject_error(BlockDriverState *bs,
     acb->bh = bh;
     qemu_bh_schedule(bh);
 
-    return (BlockDriverAIOCB*) acb;
+    return &acb->common;
 }
 
 static BlockDriverAIOCB *blkdebug_aio_readv(BlockDriverState *bs,

block/qcow.c

@@ -502,7 +502,7 @@ typedef struct QCowAIOCB {
 
 static void qcow_aio_cancel(BlockDriverAIOCB *blockacb)
 {
-    QCowAIOCB *acb = (QCowAIOCB *)blockacb;
+    QCowAIOCB *acb = container_of(blockacb, QCowAIOCB, common);
     if (acb->hd_aiocb)
         bdrv_aio_cancel(acb->hd_aiocb);
     qemu_aio_release(acb);

block/qcow2.c

@@ -338,7 +338,7 @@ typedef struct QCowAIOCB {
 
 static void qcow_aio_cancel(BlockDriverAIOCB *blockacb)
 {
-    QCowAIOCB *acb = (QCowAIOCB *)blockacb;
+    QCowAIOCB *acb = container_of(blockacb, QCowAIOCB, common);
     if (acb->hd_aiocb)
         bdrv_aio_cancel(acb->hd_aiocb);
     qemu_aio_release(acb);

block/vdi.c

@@ -469,7 +469,7 @@ static int vdi_is_allocated(BlockDriverState *bs, int64_t sector_num,
 static void vdi_aio_cancel(BlockDriverAIOCB *blockacb)
 {
     /* TODO: This code is untested. How can I get it executed? */
-    VdiAIOCB *acb = (VdiAIOCB *)blockacb;
+    VdiAIOCB *acb = container_of(blockacb, VdiAIOCB, common);
     logout("\n");
     if (acb->hd_aiocb) {
         bdrv_aio_cancel(acb->hd_aiocb);