netdev - Re: [PATCH (repost) net-next] sched: add extack for tfilter

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Date:   Thu, 10 Nov 2022 09:27:40 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Hangbin Liu <liuhangbin@...il.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH (repost) net-next] sched: add extack for tfilter_notify

On Wed, Nov 9, 2022 at 9:20 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 9 Nov 2022 20:52:37 -0500 Jamal Hadi Salim wrote:
> > TCA_XXX are local whereas NLMSGERR_ATTR_MSG global to the
> > netlink message.
>
> "Global", but they necessitate complicating the entire protocol
> to use directly.
>
> Unless we want to create a separate netlink multicast channel for
> just ext acks of a family. That's fine by me, I guess. I'm mostly
> objecting to pretending notifications are multi-msg just to reuse
> NLMSG_DONE, and forcing all notification listeners to deal with it.
>

TBH, I am struggling as well. NLMSG_DONE is really for multi-message
(with kernel state) like dumps. Could we just extend nlmsg_notify()
callers to take extack and pass it through and then have  nlmsg_notify()
do the NLM_F_ACK_TLVS dance without MULTI flag? It would have to
be backward compat and require user space changes which Hangbin's
patch avoids but will be more general.

> > Does this mean to replicate TCA_NTF_EXT_ACK
> > for all objects when needed? (qdiscs, actions, etc).
>
> The more time we spend discussing this the more I'm inclined to say
> "this is a typical tracing use case, just use the tracepoint" :(

I understand your frustration but from an operational pov it is better to deal
with one tool than two (Marcelo's point). The way i look at these uapi
discussions
is it is ok to discuss the color of the bike shed(within reason) because any
decisions made here will have a long term effect.

cheers,
jamal