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

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Date: Tue, 5 Dec 2023 06:51:18 -0800
From: Marcelo Ricardo Leitner <mleitner@...hat.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, 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 Tue, Dec 05, 2023 at 09:41:02AM +0100, Jiri Pirko wrote:
> Mon, Dec 04, 2023 at 09:10:18PM CET, jhs@...atatu.com wrote:
> >On Mon, Dec 4, 2023 at 4:49 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >>
> >> Fri, Dec 01, 2023 at 07:45:47PM CET, jhs@...atatu.com wrote:
...
> >> >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?
> >
> >For mirror it is _a copy_ of the packet so it continues up the stack
> >and you can have other actions follow it (including multiple mirrors
> >after the first mirror). For redirect the packet is TC_ACT_CONSUMED -
> >so removed from the stack processing (and cant be sent to more ports).
> >That is how mirred has always worked and i believe thats how most
> >hardware works as well.
> >So sending to multiple ports has to be mirroring semantics (most
> >hardware assumes the same semantics).
>
> You assume cloning (sending to multiple ports) means mirror,
> that is I believe a mistake. Look at it from the perspective of
> replacing device by target for each action. Currently we have:
>
> 1) mirred mirror TARGET_DEVICE
>    Clones, sends to TARGET_DEVICE and continues up the stack
> 2) mirred redirect TARGET_DEVICE
>    Sends to TARGET_DEVICE, nothing is sent up the stack
>
> For block target, there should be exacly the same semantics:
>
> 1) mirred mirror TARGET_BLOCK
>    Clones (multiple times, for each block member), sends to TARGET_BLOCK
>    and continues up the stack
> 2) mirred redirect TARGET_BLOCK
>    Clones (multiple times, for each block member - 1), sends to
>    TARGET_BLOCK, nothing is sent up the stack

This makes sense to me as well. When I first read Jamal's email I
didn't spot any confusion, but now I see there can be some. I think he
meant pretty much the same thing, referencing cascading other outputs
after blockcast (and not the inner outputs, lets say), but that's just
my interpretation. :)

  Marcelo