netdev - Re: [PATCH net-next RFC v5 4/4] net/sched: act_blockcast: Introduce blockcast tc action

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Date: Thu, 23 Nov 2023 09:38:35 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Victor Nogueira <victor@...atatu.com>, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, xiyou.wangcong@...il.com, 
	mleitner@...hat.com, vladbu@...dia.com, paulb@...dia.com, 
	pctammela@...atatu.com, netdev@...r.kernel.org, kernel@...atatu.com
Subject: Re: [PATCH net-next RFC v5 4/4] net/sched: act_blockcast: Introduce
 blockcast tc action

On Thu, Nov 23, 2023 at 9:04 AM Jiri Pirko <jiri@...nulli.us> wrote:
>
> Thu, Nov 23, 2023 at 02:37:13PM CET, jhs@...atatu.com wrote:
> >On Thu, Nov 23, 2023 at 3:51 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >>
> >> Fri, Nov 10, 2023 at 10:46:18PM CET, victor@...atatu.com wrote:
> >> >This action takes advantage of the presence of tc block ports set in the
> >> >datapath and multicasts a packet to ports on a block. By default, it will
> >> >broadcast the packet to a block, that is send to all members of the block except
> >> >the port in which the packet arrived on. However, the user may specify
> >> >the option "tx_type all", which will send the packet to all members of the
> >> >block indiscriminately.
> >> >
> >> >Example usage:
> >> >    $ tc qdisc add dev ens7 ingress_block 22
> >> >    $ tc qdisc add dev ens8 ingress_block 22
> >> >
> >> >Now we can add a filter to broadcast packets to ports on ingress block id 22:
> >> >$ tc filter add block 22 protocol ip pref 25 \
> >> >  flower dst_ip 192.168.0.0/16 action blockcast blockid 22
> >>
> >> Name the arg "block" so it is consistent with "filter add block". Make
> >> sure this is aligned netlink-wise as well.
> >>
> >>
> >> >
> >> >Or if we wish to send to all ports in the block:
> >> >$ tc filter add block 22 protocol ip pref 25 \
> >> >  flower dst_ip 192.168.0.0/16 action blockcast blockid 22 tx_type all
> >>
> >> I read the discussion the the previous version again. I suggested this
> >> to be part of mirred. Why exactly that was not addressed?
> >>
> >
> >I am the one who pushed back (in that discussion). Actions should be
> >small and specific. Like i had said in that earlier discussion it was
> >a mistake to make mirred do both mirror and redirect - they should
>
> For mirror and redirect, I agree. For redirect and redirect, does not
> make much sense. It's just confusing for the user.
>

Blockcast only emulates the mirror part. I agree redirect doesnt make
any sense because once you redirect the packet is gone.

> >have been two actions. So i feel like adding a block to mirred is
> >adding more knobs. We are also going to add dev->group as a way to
> >select what devices to mirror to. Should that be in mirred as well?
>
> I need more details.
>

You set any port you want to be mirrored to using ip link, example:
ip link set dev $DEV1 group 2
ip link set dev $DEV2 group 2
...

Then you can blockcast:
tc filter add devx protocol ip pref 25 \
  flower dst_ip 192.168.0.0/16 action blockcast group 2

cheers,
jamal

>
> >
> >cheers,
> >jamal
> >
> >> Instead of:
> >> $ tc filter add block 22 protocol ip pref 25 \
> >>   flower dst_ip 192.168.0.0/16 action blockcast blockid 22
> >> You'd have:
> >> $ tc filter add block 22 protocol ip pref 25 \
> >>   flower dst_ip 192.168.0.0/16 action mirred egress redirect block 22
> >>
> >> I don't see why we need special action for this.
> >>
> >> Regarding "tx_type all":
> >> Do you expect to have another "tx_type"? Seems to me a bit odd. Why not
> >> to have this as "no_src_skip" or some other similar arg, without value
> >> acting as a bool (flag) on netlink level.
> >>
> >>