vhost: introduce vhost_vq_avail_empty()
This patch introduces a helper which will return true if we're sure
that the available ring is empty for a specific vq. When we're not
sure, e.g vq access failure, return false instead. This could be used
for busy polling code to exit the busy loop.
Signed-off-by: Jason Wang <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 596de21..97f26f0 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1658,6 +1658,20 @@
}
EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
+/* return true if we're sure that avaiable ring is empty */
+bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+ __virtio16 avail_idx;
+ int r;
+
+ r = __get_user(avail_idx, &vq->avail->idx);
+ if (r)
+ return false;
+
+ return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
+
/* OK, now we need to know about added descriptors. */
bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index eef33b11..af5af77 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -159,6 +159,7 @@
struct vring_used_elem *heads, unsigned count);
void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
+bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
