Re: [PATCH 1/2] xt_u32 (kernel) - match arbitrary bits and bytes of a packet

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
>>>+	spin_lock_bh(&xt_u32_lock);
>>>+
>>>+	head = skb_header_pointer(skb, 0, min(skb->len,
>>>+	       sizeof(xt_u32_buffer)), xt_u32_buffer);
> 
> 
> I'd like to hear opinions about:
> 
>  * open coding skb_header_pointer
> 
>    In the "hlen - offset >= len" case in skb_header_pointer(), it just
>    returns a pointer to the existing skb without copying, in which
>    case we would not need to take a lock at all.


No special-case solutions please, this affects many netfilter modules
and we want this for all or none.

>  * use percpu buffers, with or without opencoding skb_header_pointer
>    so that cpus/threads do not have to wait for another -m u32 to finish.


Not worth the (potentially enormous) memory waste I guess.