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

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Date:   Thu, 22 Dec 2022 09:26:14 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Hangbin Liu <liuhangbin@...il.com>,
        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>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCHv2 net-next] sched: multicast sched extack messages

On 12/22/22 12:48 AM, Hangbin Liu wrote:
> 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.
> 

it is confusing as an API to send back information or debugging strings
marked as an "error message."