Subject: Re: [PATCH] pkt_sched: act_xt support new Xtables interface

From: Jamal Hadi Salim <[email-masked]>
Date: Mon, 24 Dec 2012 07:19:26 -0500

On 12-12-24 06:49 AM, Felix Fietkau wrote:

>
> After I added it as an experiment, I got distracted with other projects
> again and forgot about submitting it. Take a look at the code - if the
> approach is reasonable, I'll submit this thing for inclusion soon.
>

Excellent ;-> Simple and elegant.

Usable as is  - some minor comments.
First nitpick: The name is not very reflective, how about:
GetMarkFromConntrack or something along those lines?

> +static int tcf_connmark(struct sk_buff *skb, const struct tc_action *a,
> +		       struct tcf_result *res)
> +{
> +	struct nf_conn *c;
> +	enum ip_conntrack_info ctinfo;
> +	int proto;
> +	int r;
> +
> +	if (skb->protocol == htons(ETH_P_IP)) {
> +		if (skb->len < sizeof(struct iphdr))
> +			goto out;
> +		proto = PF_INET;
> +	} else if (skb->protocol == htons(ETH_P_IPV6)) {
> +		if (skb->len < sizeof(struct ipv6hdr))
> +			goto out;
> +		proto = PF_INET6;
> +	} else
> +		goto out;
> +

I would have said that this action is probably also not useful for 
egress qdisc path since skb->mark would already be set. It maybe worth 
checking skb->tc_verd and skipping overhead of nf_conntrack_in() call.
Look at act_mirred for such a check.

> +	r = nf_conntrack_in(dev_net(skb->dev), proto, NF_INET_PRE_ROUTING, skb);
> +	if (r != NF_ACCEPT)
> +		goto out;
> +
> +	c = nf_ct_get(skb, &ctinfo);
> +	if (!c)
> +		goto out;
> +
> +	skb->mark = c->mark;
> +	nf_conntrack_put(skb->nfct);
> +	skb->nfct = NULL;
> +
> +out:
> +	return TC_ACT_PIPE;

Ok, perhaps set tcf_action in (iproute2) user space to TC_ACT_PIPE then 
just return policy->tcf_action here.

Even better is to have a different TC_ACT_XXX returned for failure
vs success... Your success path becomes TC_ACT_PIPE and let the
user program the failure branch optionally. This would allow for 
branching to different actions if success/failure, example:
if mark is found {
    if mark is 0xa redirect to ifb0
    else
      redirect to ifb1
} else
       set mark to 3 then redirect to ifb9

etc.

Not sure if that made sense. I am under the influence of nyquil ;->

cheers,
jamal