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Date:	Thu, 03 Oct 2013 11:06:35 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shawn Bohrer <sbohrer@...advisors.com>
Cc:	David Miller <davem@...emloft.net>, tomk@...advisors.com,
	netdev <netdev@...r.kernel.org>
Subject: Re: [net-next 2/3] udp: Add udp early demux

On Thu, 2013-10-03 at 12:39 -0500, Shawn Bohrer wrote:
> On Wed, Oct 02, 2013 at 02:38:52PM -0700, Eric Dumazet wrote:
> > I suggested that for unicast, you do a limited lookup to the first
> > socket found in bucket.
> > 
> > If its an exact match, you take the socket.
> > 
> > If not, you give up, and do not scan the whole chain.
> 
> So something like the following?
> 
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 02185a5..d202e5b 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1849,7 +1849,42 @@ begin:
>  	}
>  	rcu_read_unlock();
>  	return result;
> +}
>  
> +/* For unicast we should only early demux connected sockets or we can
> + * break forwarding setups.  The chains here can be long so only check
> + * if the first socket is an exact match and if not move on.
> + */
> +static struct sock *__udp4_lib_demux_lookup(struct net *net,
> +					    __be16 loc_port, __be32 loc_addr,
> +					    __be16 rmt_port, __be32 rmt_addr,
> +					    int dif)
> +{
> +	struct sock *sk, *result;
> +	struct hlist_nulls_node *node;
> +	unsigned short hnum = ntohs(loc_port);
> +	unsigned int slot = udp_hashfn(net, hnum, udp_table.mask);
> +	struct udp_hslot *hslot = &udp_table.hash[slot];
> +	const int exact_match = 18;
> +	int score;
> +
> +	rcu_read_lock();
> +	result = NULL;
> +	sk_nulls_for_each_rcu(sk, node, &hslot->head) {
> +		score = compute_score(sk, net, rmt_addr, hnum, rmt_port,
> +				      loc_addr, loc_port, dif);
> +		if (score == exact_match)
> +			result = sk;
> +		/* Only check first socket in chain */
> +		break;
> +	}
> +
> +	if (result) {
> +		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
> +			result = NULL;
> +	}
> +	rcu_read_unlock();
> +	return result;
>  }
>  

Just do the tuple comparison instead of compute_score(),
since you know we want full L4 match.

The standard way is to use the INET_MATCH() macro



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