netdev - Re: [PATCH net-next 1/1] net sched qdisc: pass netlink message flags in event notification

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Date:   Tue, 31 Oct 2017 17:55:00 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Roman Mashak <mrv@...atatu.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net-next 1/1] net sched qdisc: pass netlink message flags
 in event notification

On Mon, Oct 30, 2017 at 2:17 PM, Roman Mashak <mrv@...atatu.com> wrote:
> Cong Wang <xiyou.wangcong@...il.com> writes:
>
>> On Mon, Oct 30, 2017 at 11:07 AM, Roman Mashak <mrv@...atatu.com> wrote:
>>> Cong Wang <xiyou.wangcong@...il.com> writes:
>>>
>>>> On Sat, Oct 28, 2017 at 8:36 PM, Roman Mashak <mrv@...atatu.com> wrote:
>>>>> Cong Wang <xiyou.wangcong@...il.com> writes:
>>>>
>>>> Hmm, I thought you use RTM_NEWQDISC+RTM_DELQDISC to
>>>> determine it is replacement, no?
>>>
>>> Create is RTM_NEWQDISC and NLM_F_EXCL|NLM_F_CREATE, replacement is
>>> RTM_NEWQDISC and NLM_F_REPLACE in netlink flags.
>>
>> Is there any reason we can't use RTM_NEWQDISC+RTM_DELQDISC
>> rather than NLM_F_REPLACE to determine it is replacement?
>>
>
> I'm not sure this would be valid semantics for replace operation, look at
> the rfc3549:
>
> Additional flag bits for NEW requests
>           NLM_F_REPLACE   Replace existing matching config object with
>                           this request.
>

I am not saying NLM_F_REPLACE is not correct, I am saying the
RTM_NEWQDISC+RTM_DELQDISC in a same message probably
exists for a reason.


>> Note, RTM_NEWQDISC+RTM_DELQDISC are put in a same
>> message not two.
>
> Hmm, could you clarify how do you expect to put two event IDs in nlmsg_type?

Looking at qdisc_notify(), it is essentially two skb_put() on a same
skb, right? So two nlmsghdr in one skb? Or I read it wrong?