linux-aio: Convert laio_aiocb_info.cancel to .cancel_async

Just call io_cancel (2), if it fails, it means the request is not
canceled, so the event loop will eventually call
qemu_laio_process_completion.

In qemu_laio_process_completion, change to call the cb unconditionally.
It is required by bdrv_aio_cancel_async.
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/linux-aio.c

@@ -85,9 +85,8 @@ static void qemu_laio_process_completion(struct qemu_laio_state *s,
                 ret = -EINVAL;
             }
         }
-
-        laiocb->common.cb(laiocb->common.opaque, ret);
     }
+    laiocb->common.cb(laiocb->common.opaque, ret);
 
     qemu_aio_release(laiocb);
 }
@@ -153,35 +152,22 @@ static void laio_cancel(BlockDriverAIOCB *blockacb)
     struct io_event event;
     int ret;
 
-    if (laiocb->ret != -EINPROGRESS)
+    if (laiocb->ret != -EINPROGRESS) {
         return;
-
-    /*
-     * Note that as of Linux 2.6.31 neither the block device code nor any
-     * filesystem implements cancellation of AIO request.
-     * Thus the polling loop below is the normal code path.
-     */
+    }
     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
-    if (ret == 0) {
-        laiocb->ret = -ECANCELED;
+    laiocb->ret = -ECANCELED;
+    if (ret != 0) {
+        /* iocb is not cancelled, cb will be called by the event loop later */
         return;
     }
 
-    /*
-     * We have to wait for the iocb to finish.
-     *
-     * The only way to get the iocb status update is by polling the io context.
-     * We might be able to do this slightly more optimal by removing the
-     * O_NONBLOCK flag.
-     */
-    while (laiocb->ret == -EINPROGRESS) {
-        qemu_laio_completion_cb(&laiocb->ctx->e);
-    }
+    laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 }
 
 static const AIOCBInfo laio_aiocb_info = {
     .aiocb_size         = sizeof(struct qemu_laiocb),
-    .cancel             = laio_cancel,
+    .cancel_async       = laio_cancel,
 };
 
 static void ioq_init(LaioQueue *io_q)