On Mon, Jul 17, 2017 at 08:43:58PM +0800, Jason Wang wrote:
> Pack headroom into ctx, then during XDP set, we could know the size of
> headroom and copy if needed. This is required for avoiding reset on
> XDP.
Not really when XDP is set - it's when buffers are used.
virtio-net: pack headroom into ctx for mergeable buffers
Pack headroom into ctx - this way when we get a buffer we can figure out
the actual headroom that was allocated for the buffer. Will be helpful
to optimize switching between XDP and non-XDP modes which have different
headroom requirements.
>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> ---
> drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1f8c15c..8fae9a8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -270,6 +270,23 @@ static void skb_xmit_done(struct virtqueue *vq)
> netif_wake_subqueue(vi->dev, vq2txq(vq));
> }
>
> +#define MRG_CTX_HEADER_SHIFT 22
> +static void *mergeable_len_to_ctx(unsigned int truesize,
> + unsigned int headroom)
> +{
> + return (void *)(unsigned long)((headroom << MRG_CTX_HEADER_SHIFT) |
> truesize);
> +}
> +
> +static unsigned int mergeable_ctx_to_headroom(void *mrg_ctx)
> +{
> + return (unsigned long)mrg_ctx >> MRG_CTX_HEADER_SHIFT;
> +}
> +
> +static unsigned int mergeable_ctx_to_truesize(void *mrg_ctx)
> +{
> + return (unsigned long)mrg_ctx & ((1 << MRG_CTX_HEADER_SHIFT) - 1);
> +}
> +
> /* Called from bottom half context */
> static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> struct receive_queue *rq,
> @@ -639,13 +656,14 @@ static struct sk_buff *receive_mergeable(struct
> net_device *dev,
> }
> rcu_read_unlock();
>
> - if (unlikely(len > (unsigned long)ctx)) {
> + truesize = mergeable_ctx_to_truesize(ctx);
> + if (unlikely(len > truesize)) {
> pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> dev->name, len, (unsigned long)ctx);
> dev->stats.rx_length_errors++;
> goto err_skb;
> }
> - truesize = (unsigned long)ctx;
> +
> head_skb = page_to_skb(vi, rq, page, offset, len, truesize);
> curr_skb = head_skb;
>
> @@ -665,13 +683,14 @@ static struct sk_buff *receive_mergeable(struct
> net_device *dev,
> }
>
> page = virt_to_head_page(buf);
> - if (unlikely(len > (unsigned long)ctx)) {
> +
> + truesize = mergeable_ctx_to_truesize(ctx);
> + if (unlikely(len > truesize)) {
> pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> dev->name, len, (unsigned long)ctx);
> dev->stats.rx_length_errors++;
> goto err_skb;
> }
> - truesize = (unsigned long)ctx;
>
> num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
> if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
> @@ -889,7 +908,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>
> buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> buf += headroom; /* advance address leaving hole at front of pkt */
> - ctx = (void *)(unsigned long)len;
> + ctx = mergeable_len_to_ctx(len, headroom);
> get_page(alloc_frag->page);
> alloc_frag->offset += len + headroom;
> hole = alloc_frag->size - alloc_frag->offset;
> --
> 2.7.4
