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    Subject[PATCH net-next V2 2/5] virtio-net: pack headroom into ctx for mergeable buffers
    Date
    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 <jasowang@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
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