netdev - Re: [PATCHv2 net-next] sched: multicast sched extack messages

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Date:   Thu, 22 Dec 2022 15:48:31 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        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>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCHv2 net-next] sched: multicast sched extack messages

On Wed, Dec 21, 2022 at 05:28:17PM -0800, Jakub Kicinski wrote:
> On Wed, 21 Dec 2022 17:39:40 +0800 Hangbin Liu wrote:
> > +	nlh = nlmsg_put(skb, portid, n->nlmsg_seq, NLMSG_ERROR, sizeof(*errmsg),
> > +			NLM_F_ACK_TLVS | NLM_F_CAPPED);
> > +	if (!nlh)
> > +		return -1;
> > +
> > +	errmsg = (struct nlmsgerr *)nlmsg_data(nlh);
> > +	errmsg->error = 0;
> > +	errmsg->msg = *n;
> > +
> > +	if (nla_put_string(skb, NLMSGERR_ATTR_MSG, extack->_msg))
> > +		return -1;
> > +
> > +	nlmsg_end(skb, nlh);
> 
> I vote "no", notifications should not generate NLMSG_ERRORs.
> (BTW setting pid and seq on notifications is odd, no?)

I'm not sure if this error message should be counted to notifications generation.
The error message is generated as there is extack message, which is from
qdisc/filter adding/deleting.

Can't we multicast error message?

If we can't multicast the extack message via NLMSG_ERROR or NLMSG_DONE. I
think there is no other way to do it via netlink.

Thanks
Hangbin