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

[Jiri Pirko <jiri@resnulli.us>]

Fri, Dec 01, 2023 at 07:45:47PM CET, jhs@mojatatu.com wrote:
>On Mon, Nov 27, 2023 at 1:52 PM Marcelo Ricardo Leitner
><mleitner@redhat.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@resnulli.us> wrote:
>> > >
>> > > Thu, Nov 23, 2023 at 05:21:51PM CET, hadi@mojatatu.com wrote:
>> > > >On Thu, Nov 23, 2023 at 10:17 AM Jiri Pirko <jiri@resnulli.us> wrote:
>> > > >>
>> > > >> Thu, Nov 23, 2023 at 03:38:35PM CET, jhs@mojatatu.com wrote:
>> > > >> >On Thu, Nov 23, 2023 at 9:04 AM Jiri Pirko <jiri@resnulli.us> wrote:
>> > > >> >>
>> > > >> >> Thu, Nov 23, 2023 at 02:37:13PM CET, jhs@mojatatu.com wrote:
>> > > >> >> >On Thu, Nov 23, 2023 at 3:51 AM Jiri Pirko <jiri@resnulli.us> wrote:
>> > > >> >> >>
>> > > >> >> >> Fri, Nov 10, 2023 at 10:46:18PM CET, victor@mojatatu.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...

Could you remind me why mirror and not redirect? Does the packet
continue through the stack?


>
>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.
>> > > >> >> >>
>> > > >> >> >>
>> >
>>