[...]
>> @@ -393,34 +397,39 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
>> struct bpf_prog *xdp_prog,
>> void *data, int len)
>> {
>> - int hdr_padded_len;
>> struct xdp_buff xdp;
>> - void *buf;
>> unsigned int qp;
>> u32 act;
>> +
>> if (vi->mergeable_rx_bufs) {
>> - hdr_padded_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
>> - xdp.data = data + hdr_padded_len;
>> + int desc_room = sizeof(struct virtio_net_hdr_mrg_rxbuf);
>> +
>> + /* Allow consuming headroom but reserve enough space to push
>> + * the descriptor on if we get an XDP_TX return code.
>> + */
>> + xdp.data_hard_start = data - vi->headroom + desc_room;
>> + xdp.data = data + desc_room;
>> xdp.data_end = xdp.data + (len - vi->hdr_len);
>> - buf = data;
>> } else { /* small buffers */
>> struct sk_buff *skb = data;
>> - xdp.data = skb->data;
>> + xdp.data_hard_start = skb->data;
>> + xdp.data = skb->data + vi->headroom;
>> xdp.data_end = xdp.data + len;
>> - buf = skb->data;
>> }
>> act = bpf_prog_run_xdp(xdp_prog, &xdp);
>> switch (act) {
>> case XDP_PASS:
>> + if (!vi->mergeable_rx_bufs)
>> + __skb_pull((struct sk_buff *) data,
>> + xdp.data - xdp.data_hard_start);
>
> Instead of doing things here and virtnet_xdp_xmit(). How about always making
> skb->data point to the buffer head like:
>
> 1) reserve headroom in add_recvbuf_small()
> 2) skb_push(xdp->data - xdp_data_hard_start, skb) if we detect xdp->data was
> modified afer bpf_prog_run_xdp()
>
> Then there's no special code in either XDP_PASS or XDP_TX?
>
Alternatively moving the pull into the receive_small XDP handler also
removes the special case. I'll submit a patch shortly let me know what
you think.
>> return XDP_PASS;
>> case XDP_TX:
>> qp = vi->curr_queue_pairs -
>> vi->xdp_queue_pairs +
>> smp_processor_id();
>
> [...]
>
.John
