netdev - Re: [v4 PATCH 1/2] NETFILTER module xt_hmark, new target for HASH based fwmark

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Date:	Fri, 25 Nov 2011 15:43:52 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hans Schillstrom <hans@...illstrom.com>
Cc:	kaber@...sh.net, pablo@...filter.org, jengelh@...ozas.de,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	hans.schillstrom@...csson.com
Subject: Re: [v4 PATCH 1/2] NETFILTER module xt_hmark, new target for HASH
 based fwmark

Le vendredi 25 novembre 2011 à 10:36 +0100, Hans Schillstrom a écrit :
> From: Hans Schillstrom <hans.schillstrom@...csson.com>
> 
> The target allows you to create rules in the "raw" and "mangle" tables
> which alter the netfilter mark (nfmark) field within a given range.
> First a 32 bit hash value is generated then modulus by <limit> and
> finally an offset is added before it's written to nfmark.
> Prior to routing, the nfmark can influence the routing method (see
> "Use netfilter MARK value as routing key") and can also be used by
> other subsystems to change their behavior.
> 


Oh well, yet another duplicated flow dissector ...

> +/*
> + * Calc hash value, special casre is taken on icmp and fragmented messages
> + * i.e. fragmented messages don't use ports.
> + */
> +__u32 hmark_v6(struct sk_buff *skb, const struct xt_action_param *par)
> +{
> +	struct xt_hmark_info *info = (struct xt_hmark_info *)par->targinfo;



> +no6ports:
> +	nexthdr &= info->prmask;
> +	/* get a consistent hash (same value on both flow directions) */
> +	if (addr2 < addr1)
> +		swap(addr1, addr2);
> +	hash = jhash_3words(addr1, addr2, ports.v32, info->hashrnd) ^ nexthdr;

whats the point computing hash, if info->hmod is null, since we dont set
skb->mark ?

> +	if (info->hmod)
> +		skb->mark = (hash % info->hmod) + info->hoffs;
> +
> +	return XT_CONTINUE;
> +}
> +#endif
> +


Same problem/question on hmark_v4()


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