On Thu, Sep 06, 2018 at 12:05:25PM +0800, Jason Wang wrote:
> This patch implement TUN_MSG_PTR msg_control type. This type allows
> the caller to pass an array of XDP buffs to tuntap through ptr field
> of the tun_msg_control. Tap will build skb through those XDP buffers.
>
> This will avoid lots of indirect calls thus improves the icache
> utilization and allows to do XDP batched flushing when doing XDP
> redirection.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> drivers/net/tap.c | 73 +++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 71 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index 7996ed7cbf18..50eb7bf22225 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -1146,14 +1146,83 @@ static const struct file_operations tap_fops = {
> #endif
> };
>
> +static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
> +{
> + struct virtio_net_hdr *gso = xdp->data_hard_start + sizeof(int);
> + int buflen = *(int *)xdp->data_hard_start;
> + int vnet_hdr_len = 0;
> + struct tap_dev *tap;
> + struct sk_buff *skb;
> + int err, depth;
> +
> + if (q->flags & IFF_VNET_HDR)
> + vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
> +
> + skb = build_skb(xdp->data_hard_start, buflen);
> + if (!skb) {
> + err = -ENOMEM;
> + goto err;
> + }
So fundamentally why is it called XDP?
We just build and skb, don't we?
> +
> + skb_reserve(skb, xdp->data - xdp->data_hard_start);
> + skb_put(skb, xdp->data_end - xdp->data);
> +
> + skb_set_network_header(skb, ETH_HLEN);
> + skb_reset_mac_header(skb);
> + skb->protocol = eth_hdr(skb)->h_proto;
> +
> + if (vnet_hdr_len) {
> + err = virtio_net_hdr_to_skb(skb, gso, tap_is_little_endian(q));
> + if (err)
> + goto err_kfree;
> + }
> +
> + skb_probe_transport_header(skb, ETH_HLEN);
> +
> + /* Move network header to the right position for VLAN tagged packets */
> + if ((skb->protocol == htons(ETH_P_8021Q) ||
> + skb->protocol == htons(ETH_P_8021AD)) &&
> + __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
> + skb_set_network_header(skb, depth);
> +
> + rcu_read_lock();
> + tap = rcu_dereference(q->tap);
> + if (tap) {
> + skb->dev = tap->dev;
> + dev_queue_xmit(skb);
> + } else {
> + kfree_skb(skb);
> + }
> + rcu_read_unlock();
> +
> + return 0;
> +
> +err_kfree:
> + kfree_skb(skb);
> +err:
> + rcu_read_lock();
> + tap = rcu_dereference(q->tap);
> + if (tap && tap->count_tx_dropped)
> + tap->count_tx_dropped(tap);
> + rcu_read_unlock();
> + return err;
> +}
> +
> static int tap_sendmsg(struct socket *sock, struct msghdr *m,
> size_t total_len)
> {
> struct tap_queue *q = container_of(sock, struct tap_queue, sock);
> struct tun_msg_ctl *ctl = m->msg_control;
> + struct xdp_buff *xdp;
> + int i;
>
> - if (ctl && ctl->type != TUN_MSG_UBUF)
> - return -EINVAL;
> + if (ctl && ((ctl->type & 0xF) == TUN_MSG_PTR)) {
> + for (i = 0; i < ctl->type >> 16; i++) {
> + xdp = &((struct xdp_buff *)ctl->ptr)[i];
> + tap_get_user_xdp(q, xdp);
> + }
> + return 0;
> + }
>
> return tap_get_user(q, ctl ? ctl->ptr : NULL, &m->msg_iter,
> m->msg_flags & MSG_DONTWAIT);
> --
> 2.17.1
