quorum: Fix crash in quorum_aio_cb()

quorum_aio_cb() emits the QUORUM_REPORT_BAD event if there's
an I/O error in a Quorum child. However sacb->aiocb must be
correctly initialized for this to happen. read_quorum_children() and
read_fifo_child() are not doing this, which results in a QEMU crash.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Message-id: 8138570d071ba7e25db3736979234a1fd71dbd05.1457610443.git.berto@igalia.com
Signed-off-by: NMax Reitz <mreitz@redhat.com>

block/quorum.c

@@ -655,8 +655,9 @@ static BlockAIOCB *read_quorum_children(QuorumAIOCB *acb)
     }
 
     for (i = 0; i < s->num_children; i++) {
-        bdrv_aio_readv(s->children[i]->bs, acb->sector_num, &acb->qcrs[i].qiov,
-                       acb->nb_sectors, quorum_aio_cb, &acb->qcrs[i]);
+        acb->qcrs[i].aiocb = bdrv_aio_readv(s->children[i]->bs, acb->sector_num,
+                                            &acb->qcrs[i].qiov, acb->nb_sectors,
+                                            quorum_aio_cb, &acb->qcrs[i]);
     }
 
     return &acb->common;
@@ -671,9 +672,10 @@ static BlockAIOCB *read_fifo_child(QuorumAIOCB *acb)
     qemu_iovec_init(&acb->qcrs[acb->child_iter].qiov, acb->qiov->niov);
     qemu_iovec_clone(&acb->qcrs[acb->child_iter].qiov, acb->qiov,
                      acb->qcrs[acb->child_iter].buf);
-    bdrv_aio_readv(s->children[acb->child_iter]->bs, acb->sector_num,
-                   &acb->qcrs[acb->child_iter].qiov, acb->nb_sectors,
-                   quorum_aio_cb, &acb->qcrs[acb->child_iter]);
+    acb->qcrs[acb->child_iter].aiocb =
+        bdrv_aio_readv(s->children[acb->child_iter]->bs, acb->sector_num,
+                       &acb->qcrs[acb->child_iter].qiov, acb->nb_sectors,
+                       quorum_aio_cb, &acb->qcrs[acb->child_iter]);
 
     return &acb->common;
 }