netdev - Re: [PATCH net-next] docs: netlink: clarify the historical baggage of Netlink flags

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Message-ID: <e4db8d52-5bbb-8667-86a6-c7a2154598d1@blackwall.org>
Date:   Wed, 28 Sep 2022 12:21:57 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     nicolas.dichtel@...nd.com,
        Florent Fourcot <florent.fourcot@...irst.fr>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com
Cc:     Johannes Berg <johannes@...solutions.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Guillaume Nault <gnault@...hat.com>,
        Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH net-next] docs: netlink: clarify the historical baggage of
 Netlink flags

On 28/09/2022 11:55, Nicolas Dichtel wrote:
> 
> Hello,
> 
> Le 28/09/2022 à 10:04, Florent Fourcot a écrit :
>> Hello,
>>
>> About NLM_F_EXCL, I'm not sure that my comment is relevant for your intro.rst
>> document, but it has another usage in ipset submodule. For IPSET_CMD_DEL,
>> setting NLM_F_EXCL means "raise an error if entry does not exist before the
>> delete".
> So NLM_F_EXCL could be used with DEL command for netfilter netlink but cannot be
> used (it overlaps with NLM_F_BULK, see [1]) with DEL command for rtnetlink.
> Sigh :(
> 
> [1] https://lore.kernel.org/netdev/0198618f-7b52-3023-5e9f-b38c49af1677@6wind.com/
> 
> 
> Regards,
> Nicolas

One could argue that's abuse of the api, but since it's part of a different family
I guess it's ok. NLM_F_EXCL is a modifier of NEW cmd as the comment above it says
and has never had rtnetlink DEL users.