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Date: Sat, 12 Oct 2019 16:41:32 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: prashantbhole.linux@...il.com
Cc: Jason Wang <jasowang@...hat.com>,
"David S . Miller" <davem@...emloft.net>,
David Ahern <dsahern@...il.com>, kvm@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] vhost_net: user tap recvmsg api to access
ptr ring
On Sat, Oct 12, 2019 at 10:53:56AM +0900, prashantbhole.linux@...il.com wrote:
> From: Prashant Bhole <prashantbhole.linux@...il.com>
>
> 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.
> Signed-off-by: Prashant Bhole <prashantbhole.linux@...il.com>
> ---
> 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
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