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Subject: Re: [PATCH net-next 1/2] net/sched: sch_ingress: Support clsact
 egress mini-Qdisc option
To:     Peilin Ye <yepeilin.cs@gmail.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>,
        Peilin Ye <peilin.ye@bytedance.com>, ast@kernel.org,
        john.fastabend@gmail.com
References: <1931ca440b47344fe357d5438aeab4b439943d10.1627936393.git.peilin.ye@bytedance.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <672e6f13-bf58-d542-6712-e6f803286373@iogearbox.net>
Date:   Mon, 2 Aug 2021 23:10:56 +0200
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On 8/2/21 10:49 PM, Peilin Ye wrote:
> From: Peilin Ye <peilin.ye@bytedance.com>
> 
> If the ingress Qdisc is in use, currently it is not possible to add
> another clsact egress mini-Qdisc to the same device without taking down
> the ingress Qdisc, since both sch_ingress and sch_clsact use the same
> handle (0xFFFF0000).
> 
> Add a "change" option for sch_ingress, so that users can enable or disable
> a clsact egress mini-Qdisc, without suffering from downtime:
> 
>      $ tc qdisc add dev eth0 ingress
>      $ tc qdisc change dev eth0 ingress clsact-on
> 
> Then users can add filters to the egress mini-Qdisc as usual:
> 
>      $ tc filter add dev eth0 egress protocol ip prio 10 \
> 	    matchall action skbmod swap mac
> 
> Deleting the ingress Qdisc removes the egress mini-Qdisc as well.  To
> remove egress mini-Qdisc only, use:
> 
>      $ tc qdisc change dev eth0 ingress clsact-off
> 
> Finally, if the egress mini-Qdisc is enabled, the "show" command will
> print out a "clsact" flag to indicate it:
> 
>      $ tc qdisc show ingress
>      qdisc ingress ffff: dev eth0 parent ffff:fff1 ----------------
>      $ tc qdisc change dev eth0 ingress clsact-on
>      $ tc qdisc show ingress
>      qdisc ingress ffff: dev eth0 parent ffff:fff1 ---------------- clsact
> 
> Reviewed-by: Cong Wang <cong.wang@bytedance.com>
> Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>

NAK, just use clsact qdisc in the first place which has both ingress and egress
support instead of adding such hack. You already need to change your scripts for
clsact-on, so just swap 'tc qdisc add dev eth0 ingress' to 'tc qdisc add dev eth0
clsact' w/o needing to change kernel.

Thanks,
Daniel