netdev - Re: [PATCH/RFC net-next v2 4/4] net/sched: cls_flower: allow control of tree traversal on packet parse errors

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Date:   Fri, 5 May 2017 15:44:58 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     Jiri Pirko <jiri@...lanox.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Dinan Gunawardena <dinan.gunawardena@...ronome.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com,
        Benjamin LaHaise <benjamin.lahaise@...ronome.com>
Subject: Re: [PATCH/RFC net-next v2 4/4] net/sched: cls_flower: allow control
 of tree traversal on packet parse errors

On Fri, May 5, 2017 at 5:47 AM, Simon Horman <simon.horman@...ronome.com> wrote:
>
>  # tc qdisc del dev eth0 ingress; tc qdisc add dev eth0 ingress
>  # tc filter add dev eth0 protocol ip parent ffff: flower \
>        indev eth0 ip_proto udp dst_port 80 truncated drop action continue
>
[...]
> @@ -188,7 +189,7 @@ static int fl_classify(struct sk_buff *skb, const struct tcf_proto *tp,
>          */
>         skb_key.basic.n_proto = skb->protocol;
>         if (!skb_flow_dissect(skb, &head->dissector, &skb_key, 0))
> -               return -1;
> +               return head->err_action;

This design looks odd, if you consider matching truncated packets as
a filter like other normal filters, then you should rely on the action
appended to return the action code, not within the filter itself.