Re: [PATCH 1/3] virtio: add virtioqueue_more_used()

On Tue, May 25, 2021 at 10:23:39AM +0800, Jason Wang wrote:

在 2021/5/20 下午10:13, Stefan Hajnoczi 写道:

quoted

Add an API to check whether there are pending used buffers. There is
already a similar API called virtqueue_poll() but it only works together
with virtqueue_enable_cb_prepare(). The patches that follow add blk-mq
->poll() support to virtio_blk and they need to check for used buffers
without re-enabling virtqueue callbacks, so introduce an API for it.

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

Typo in the subject.

Thanks, will fix.

quoted

+/**
+ * virtqueue_more_used - check if there are used buffers pending
+ * @_vq: the struct virtqueue we're talking about.
+ *
+ * Returns true if there are used buffers, false otherwise. May be called at
+ * the same time as other virtqueue operations, but actually calling
+ * virtqueue_get_buf() requires serialization so be mindful of the race between
+ * calling virtqueue_more_used() and virtqueue_get_buf().
+ */
+bool virtqueue_more_used(const struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	return more_used(vq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_more_used);

It's worth to mention that the function is not serialized (no barriers).

Thanks, will fix.

Stefan