Re: [PATCH] net: increase skb->users instead of skb_clone()

Eric Dumazet
2010-12-16T14:31:03Z

Le jeudi 16 décembre 2010 à 22:20 +0800, Junchang Wang a écrit :
> On Thu, Dec 16, 2010 at 3:23 PM, Changli Gao <xiaosuo@gmail.com> wrote:
>
> >> You beat me, but I was thinking of a different way, adding a new
> >> pt_prev->xmit_func(), handling all the details (no need for atomic ops
> >> on skb users if packet is not delivered at all).
> >>
> >> By the way, your patch is not 100% safe/OK, because af_packet rcv()
> >> handler writes on skb (skb_pull() and all)
> >>
> >
> > But af_packet_rcv() restores skbs at last.
> >
> > if (skb_head != skb->data && skb_shared(skb)) {
> > skb->data = skb_head;
> > skb->len = skb_len;
> > }
> >
> If af packet_rcv invokes skb_clone, this skb is differ from the original one.
> Eric's warning is right.

It was a false alarm.

If packet_rcv() invokes skb_clone(), skb still points to original skb.
No worry.