Re: [PATCH net-next 2/3] vhost_net: user tap recvmsg api to access ptr ring

Prashant Bhole <prashantbhole.linux@xxxxxxxxx> · Tue, 15 Oct 2019 09:57:11 +0900

Hi Michael,
Thanks for reviewing.

On 10/13/19 5:41 AM, Michael S. Tsirkin wrote:
On Sat, Oct 12, 2019 at 10:53:56AM +0900, prashantbhole.linux@xxxxxxxxx wrote:
From: Prashant Bhole <prashantbhole.linux@xxxxxxxxx>

Currently vhost_net directly accesses ptr ring of tap driver to
fetch Rx packet pointers. In order to avoid it this patch modifies
tap driver's recvmsg api to do additional task of fetching Rx packet
pointers.

A special struct tun_msg_ctl is already being usedd via msg_control
for tun Rx XDP batching. This patch extends tun_msg_ctl usage to
send sub commands to recvmsg api. recvmsg can now produce/unproduce
pointers from ptr ring as an additional task.

This will be useful in future in implementation of virtio-net XDP
offload feature. Where packets will be XDP batch processed in
tun_recvmsg.

I'd like to see that future patch, by itself this patchset
seems to be of limited usefulness.

Agree, this set is just a reorganization. Next time this will be a part
of set which actually uses it.

Thanks


Signed-off-by: Prashant Bhole <prashantbhole.linux@xxxxxxxxx>
---
  drivers/net/tap.c      | 22 +++++++++++++++++++-
  drivers/net/tun.c      | 24 +++++++++++++++++++++-
  drivers/vhost/net.c    | 46 +++++++++++++++++++++++++++++++++---------
  include/linux/if_tun.h |  3 +++
  4 files changed, 83 insertions(+), 12 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 01bd260ce60c..3d0bf382dbbc 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -1234,8 +1234,28 @@ static int tap_recvmsg(struct socket *sock, struct msghdr *m,
  		       size_t total_len, int flags)
  {
  	struct tap_queue *q = container_of(sock, struct tap_queue, sock);
-	struct sk_buff *skb = m->msg_control;
+	struct tun_msg_ctl *ctl = m->msg_control;
+	struct sk_buff *skb = NULL;
  	int ret;
+
+	if (ctl) {
+		switch (ctl->cmd) {
+		case TUN_CMD_PACKET:
+			skb = ctl->ptr;
+			break;
+		case TUN_CMD_PRODUCE_PTRS:
+			return ptr_ring_consume_batched(&q->ring,
+							ctl->ptr_array,
+							ctl->num);
+		case TUN_CMD_UNPRODUCE_PTRS:
+			ptr_ring_unconsume(&q->ring, ctl->ptr_array, ctl->num,
+					   tun_ptr_free);
+			return 0;
+		default:
+			return -EINVAL;
+		}
+	}
+
  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC)) {
  		kfree_skb(skb);
  		return -EINVAL;
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 29711671959b..7d4886f53389 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2577,7 +2577,8 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
  {
  	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
  	struct tun_struct *tun = tun_get(tfile);
-	void *ptr = m->msg_control;
+	struct tun_msg_ctl *ctl = m->msg_control;
+	void *ptr = NULL;
  	int ret;
  
  	if (!tun) {
@@ -2585,6 +2586,27 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
  		goto out_free;
  	}
  
+	if (ctl) {
+		switch (ctl->cmd) {
+		case TUN_CMD_PACKET:
+			ptr = ctl->ptr;
+			break;
+		case TUN_CMD_PRODUCE_PTRS:
+			ret = ptr_ring_consume_batched(&tfile->tx_ring,
+						       ctl->ptr_array,
+						       ctl->num);
+			goto out;
+		case TUN_CMD_UNPRODUCE_PTRS:
+			ptr_ring_unconsume(&tfile->tx_ring, ctl->ptr_array,
+					   ctl->num, tun_ptr_free);
+			ret = 0;
+			goto out;
+		default:
+			ret = -EINVAL;
+			goto out_put_tun;
+		}
+	}
+
  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
  		ret = -EINVAL;
  		goto out_put_tun;
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 5946d2775bd0..5e5c1063606c 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -175,24 +175,44 @@ static void *vhost_net_buf_consume(struct vhost_net_buf *rxq)
  
  static int vhost_net_buf_produce(struct vhost_net_virtqueue *nvq)
  {
+	struct vhost_virtqueue *vq = &nvq->vq;
+	struct socket *sock = vq->private_data;
  	struct vhost_net_buf *rxq = &nvq->rxq;
+	struct tun_msg_ctl ctl = {
+		.cmd = TUN_CMD_PRODUCE_PTRS,
+		.ptr_array = rxq->queue,
+		.num = VHOST_NET_BATCH,
+	};
+	struct msghdr msg = {
+		.msg_control = &ctl,
+	};
  
  	rxq->head = 0;
-	rxq->tail = ptr_ring_consume_batched(nvq->rx_ring, rxq->queue,
-					      VHOST_NET_BATCH);
+	rxq->tail = sock->ops->recvmsg(sock, &msg, 0, 0);
+	if (rxq->tail < 0)
+		rxq->tail = 0;
+
  	return rxq->tail;
  }
  
  static void vhost_net_buf_unproduce(struct vhost_net_virtqueue *nvq)
  {
+	struct vhost_virtqueue *vq = &nvq->vq;
+	struct socket *sock = vq->private_data;
  	struct vhost_net_buf *rxq = &nvq->rxq;
+	struct tun_msg_ctl ctl = {
+		.cmd = TUN_CMD_UNPRODUCE_PTRS,
+		.ptr_array = rxq->queue + rxq->head,
+		.num = vhost_net_buf_get_size(rxq),
+	};
+	struct msghdr msg = {
+		.msg_control = &ctl,
+	};
  
-	if (nvq->rx_ring && !vhost_net_buf_is_empty(rxq)) {
-		ptr_ring_unconsume(nvq->rx_ring, rxq->queue + rxq->head,
-				   vhost_net_buf_get_size(rxq),
-				   tun_ptr_free);
-		rxq->head = rxq->tail = 0;
-	}
+	if (!vhost_net_buf_is_empty(rxq))
+		sock->ops->recvmsg(sock, &msg, 0, 0);
+
+	rxq->head = rxq->tail = 0;
  }
  
  static int vhost_net_buf_peek_len(void *ptr)
@@ -1109,6 +1129,9 @@ static void handle_rx(struct vhost_net *net)
  		.flags = 0,
  		.gso_type = VIRTIO_NET_HDR_GSO_NONE
  	};
+	struct tun_msg_ctl ctl = {
+		.cmd = TUN_CMD_PACKET,
+	};
  	size_t total_len = 0;
  	int err, mergeable;
  	s16 headcount;
@@ -1166,8 +1189,11 @@ static void handle_rx(struct vhost_net *net)
  			goto out;
  		}
  		busyloop_intr = false;
-		if (nvq->rx_ring)
-			msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
+		if (nvq->rx_ring) {
+			ctl.cmd = TUN_CMD_PACKET;
+			ctl.ptr = vhost_net_buf_consume(&nvq->rxq);
+			msg.msg_control = &ctl;
+		}
  		/* On overrun, truncate and discard */
  		if (unlikely(headcount > UIO_MAXIOV)) {
  			iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
index bdfa671612db..8608d4095143 100644
--- a/include/linux/if_tun.h
+++ b/include/linux/if_tun.h
@@ -13,10 +13,13 @@
  
  #define TUN_CMD_PACKET 1
  #define TUN_CMD_BATCH  2
+#define TUN_CMD_PRODUCE_PTRS	3
+#define TUN_CMD_UNPRODUCE_PTRS	4
  struct tun_msg_ctl {
  	unsigned short cmd;
  	unsigned short num;
  	void *ptr;
+	void **ptr_array;
  };
  
  struct tun_xdp_hdr {
--
2.21.0






