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    SubjectRe: alloc skb based on a given data buffer
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    From: Zhu Yi <yi.zhu@intel.com>
    Date: Tue, 15 Sep 2009 16:57:29 +0800

    > Thanks. So we can put the 8K buffer into 2 skb_shinfo()->frags[] slots
    > and set nr_frags to 2, right? Is this supported allover the network code
    > already? At a first glance, I didn't find any frags handling in mac80211
    > stack.

    You have to pre-pull the link level protocol headers into the
    linear area, but that's it.

    Again, see niu.c for details, it does:

    static void niu_rx_skb_append(struct sk_buff *skb, struct page *page,
    u32 offset, u32 size)
    {
    int i = skb_shinfo(skb)->nr_frags;
    skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

    frag->page = page;
    frag->page_offset = offset;
    frag->size = size;

    skb->len += size;
    skb->data_len += size;
    skb->truesize += size;

    skb_shinfo(skb)->nr_frags = i + 1;
    }

    to add pages to SKBs and then at the end it goes:

    skb_reserve(skb, NET_IP_ALIGN);
    __pskb_pull_tail(skb, min(len, NIU_RXPULL_MAX));

    Right before giving the SKB to the networking stack. NIU_RXPULL_MAX
    should be a value that will be large enough to cover the largest
    possible link level header.


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