[PATCH] virtio: Introduce a new kick interface virtqueue_kick_try()

[Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>]

Unlike virtqueue_kick(), virtqueue_kick_try() returns true only when the
kick is successful. In virtio-net, we want to count the number of kicks.
So we need an interface that can perceive whether the kick is actually
executed.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/net/virtio_net.c     |  8 ++++----
 drivers/virtio/virtio_ring.c | 20 ++++++++++++++++++++
 include/linux/virtio.h       |  2 ++
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9b6a4a875c55..167697030cb6 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -617,7 +617,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	ret = nxmit;
 
 	if (flags & XDP_XMIT_FLUSH) {
-		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq))
+		if (virtqueue_kick_try(sq->vq))
 			kicks = 1;
 	}
 out:
@@ -1325,7 +1325,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
 		if (err)
 			break;
 	} while (rq->vq->num_free);
-	if (virtqueue_kick_prepare(rq->vq) && virtqueue_notify(rq->vq)) {
+	if (virtqueue_kick_try(rq->vq)) {
 		unsigned long flags;
 
 		flags = u64_stats_update_begin_irqsave(&rq->stats.syncp);
@@ -1533,7 +1533,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 
 	if (xdp_xmit & VIRTIO_XDP_TX) {
 		sq = virtnet_xdp_get_sq(vi);
-		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
+		if (virtqueue_kick_try(sq->vq)) {
 			u64_stats_update_begin(&sq->stats.syncp);
 			sq->stats.kicks++;
 			u64_stats_update_end(&sq->stats.syncp);
@@ -1710,7 +1710,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	if (kick || netif_xmit_stopped(txq)) {
-		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
+		if (virtqueue_kick_try(sq->vq)) {
 			u64_stats_update_begin(&sq->stats.syncp);
 			sq->stats.kicks++;
 			u64_stats_update_end(&sq->stats.syncp);
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..1462be756875 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1874,6 +1874,26 @@ bool virtqueue_kick(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick);
 
+/**
+ * virtqueue_kick_try - try update after add_buf
+ * @vq: the struct virtqueue
+ *
+ * After one or more virtqueue_add_* calls, invoke this to kick
+ * the other side.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ *
+ * Returns true if kick success, otherwise false.
+ */
+bool virtqueue_kick_try(struct virtqueue *vq)
+{
+	if (virtqueue_kick_prepare(vq) && virtqueue_notify(vq))
+		return true;
+	return false;
+}
+EXPORT_SYMBOL_GPL(virtqueue_kick_try);
+
 /**
  * virtqueue_get_buf - get the next used buffer
  * @_vq: the struct virtqueue we're talking about.
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b1894e0323fa..45cd6a0af24d 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -59,6 +59,8 @@ int virtqueue_add_sgs(struct virtqueue *vq,
 
 bool virtqueue_kick(struct virtqueue *vq);
 
+bool virtqueue_kick_try(struct virtqueue *vq);
+
 bool virtqueue_kick_prepare(struct virtqueue *vq);
 
 bool virtqueue_notify(struct virtqueue *vq);
-- 
2.31.0

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