Date: Fri, 1 Dec 2023 13:45:47 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Marcelo Ricardo Leitner <mleitner@...hat.com>
Cc: Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <hadi@...atatu.com>, 
	Victor Nogueira <victor@...atatu.com>, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, xiyou.wangcong@...il.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 Mon, Nov 27, 2023 at 1:52 PM Marcelo Ricardo Leitner
<mleitner@...hat.com> wrote:
>
> On Mon, Nov 27, 2023 at 10:50:48AM -0500, Jamal Hadi Salim wrote:
> > On Thu, Nov 23, 2023 at 11:52 AM Jiri Pirko <jiri@...nulli.us> wrote:
> > >
> > > Thu, Nov 23, 2023 at 05:21:51PM CET, hadi@...atatu.com wrote:
> > > >On Thu, Nov 23, 2023 at 10:17 AM Jiri Pirko <jiri@...nulli.us> wrote:
> > > >>
> > > >> Thu, Nov 23, 2023 at 03:38:35PM CET, jhs@...atatu.com wrote:
> > > >> >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.
> > > >>
> > > >> How is it mirror? It is redirect to multiple, isn't it?
> > > >>
> > > >>
> > > >> >
> > > >> >> >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
> > > >>
> > > >> That does not looks correct at all. Do tc stuff in tc, no?
> > > >>
> > > >>
> > > >> >...
> > > >> >
> > > >> >Then you can blockcast:
> > > >> >tc filter add devx protocol ip pref 25 \
> > > >> >  flower dst_ip 192.168.0.0/16 action blockcast group 2
> > > >>
> > > >> "blockcasting" to something that is not a block anymore. Not nice.
>
> +1
>
> > > >>
> > > >
> > > >Sorry, missed this one. Yes blockcasting is no longer appropriate  -
> > > >perhaps a different action altogether.
> > >
> > > mirret redirect? :)
> > >
> > > With target of:
> > > 1) dev (the current one)
> > > 2) block
> > > 3) group
> > > ?
> >
> > tbh, I dont like it - but we need to make progress. I will defer to Marcelo.
>
> With the addition of a new output type that I didn't foresee, that
> AFAICS will use the same parameters as the block output, creating a
> new action for it is a lot of boilerplate for just having a different
> name. If these new two actions can share parsing code and everything,
> then it's not too far for mirred also use. And if we stick to the
> concept of one single action for outputting to multiple interfaces,
> even just deciding on the new name became quite challenging now.
> "groupcast" is misleading. "multicast" no good, "multimirred" not
> intuitive, "supermirred" what? and so on..
>
> I still think that it will become a very complex action, but well,
> hopefully the man page can be updated in a way to minimize the
> confusion.

Ok, so we are moving forward with mirred "mirror" option only for this then...

cheers,
jamal

> Cheers,
> Marcelo
>
> >
> > cheers,
> > jamal
> >
> > >
> > > >
> > > >cheers,
> > > >jamal
> > > >> >
> > > >> >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.
> > > >> >> >>
> > > >> >> >>
> >
>

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