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

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Date:   Wed, 28 Sep 2022 17:40:17 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, 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>,
        Florent Fourcot <florent.fourcot@...irst.fr>,
        Guillaume Nault <gnault@...hat.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH net-next] docs: netlink: clarify the historical baggage of
 Netlink flags

On 28/09/2022 17:21, Jakub Kicinski wrote:
> On Wed, 28 Sep 2022 10:03:07 +0300 Nikolay Aleksandrov wrote:
>> The part about NLM_F_BULK is correct now, but won't be soon. I have patches to add
>> bulk delete to mdbs as well, and IIRC there were plans for other object types.
>> I can update the doc once they are applied, but IMO it will be more useful to explain
>> why they are used instead of who's using them, i.e. the BULK was added to support
>> flush for FDBs w/ filtering initially and it's a flag so others can re-use it
>> (my first attempt targeted only FDBs[1], but after a discussion it became clear that
>> it will be more beneficial if other object types can re-use it so moved to a flag).
>> The first version of the fdb flush support used only netlink attributes to do the
>> flush via setlink, later moved to a specific RTM command (RTM_FLUSHNEIGH)[2] and
>> finally settled on the flag[3][4] so everyone can use it.
> 
> I thought that's all FDB-ish stuff. Not really looking forward to the
> use of flags spreading but within rtnl it may make some sense. We can
> just update the docs tho, no?
> 

Sure, that's ok.

> BTW how would you define the exact semantics of NLM_F_BULK vs it not
> being set, in abstract terms?

Well, BULK is a delete modified to act on multiple objects, so I'd say if it is not
set the DELETE targets a single object vs multiple objects if set. Obviously in more
formal terms, sorry not at a PC right now. :)