Subject: Re: [PATCH net-next] tc: fix tc actions in case of shared skb

From: Alexei Starovoitov <[email-masked]>
Date: Mon, 13 Jul 2015 15:26:46 -0700

On 7/13/15 1:55 PM, Daniel Borkmann wrote:
> On 07/13/2015 10:17 PM, Alexei Starovoitov wrote:
> ...
>> We cannot check tc actions from pktgen, since they can be added
>> dynamically.
>> So I see three options:
>> 1 get rid of burst hack for both RX and TX in pktgen (kills performance)
>> 2 add unlikely(skb_shread) check to few tc actions
>> 3 do nothing
...
> pktgen case. :/ With regards to option 2, you could hide that behind
> a static inline helper wrapped in IS_ENABLED(CONFIG_NET_PKTGEN), but
> that is a veeeery ugly workaround/hack as well (and distros might
> even ship it nevertheless).

naming such helper is a headache as well.
static inline bool is_pktgen_shared_skb(struct sk_buff *skb)
{
#if IS_ENABLED(CONFIG_NET_PKTGEN)
	/* pktgen uses skb->users += burst trick to reuse skb */
	return skb_shared(skb);
#else
	return false;
#endif
}
and in actions:
if (unlikely(is_pktgen_shared_skb(skb))) goto drop;

thoughts?