Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages

[David Miller]

From: Alban Crequy <alban.crequy@xxxxxxxxxxxxxxx>
Date: Tue, 23 Nov 2010 17:47:01 +0000

> Le Tue, 23 Nov 2010 17:08:37 +0100,
> Eric Dumazet <eric.dumazet@xxxxxxxxx> a écrit :
>> I am not sure if doing 90 clones of skb and filtering them one by one
>> is going to be fast :-(
> 
> Yes... I think it can be optimized. Run the socket filter first by
> calling sk_run_filter() directly and then call skb_clone() + pskb_trim()
> only on the few remaining sockets.

BTW, we have and have talked about the same exact problem with
AF_PACKET socket users such as DHCP.

We clone and push the packet down into the AF_PACKET protocol
code from the pt_type callback when %99 of the time the socket
filter doesn't match and thus the clone is completely wasted
work.

If we know the socket, or more specifically the filter, early enough,
we could have a special interface like:

	struct sk_buff *skb_filter_or_clone(struct sk_buff *skb, ...)

Which returns a non-NULL cloned SKB if the filter accepts the
packet.
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