netdev - Re: [Question] Should NLMSG_DONE has flag NLM_F

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Date:   Wed, 24 Aug 2022 18:39:45 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     netdev@...r.kernel.org, Dmitry Safonov <0x7f454c46@...il.com>,
        Florian Westphal <fw@...len.de>,
        Arkadi Sharshevsky <arkadis@...lanox.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Question] Should NLMSG_DONE has flag NLM_F_MULTI?

On Wed, 24 Aug 2022 11:20:18 +0800 Hangbin Liu wrote:
> When checking the NLMSG_DONE message in kernel, I saw lot of functions would
> set NLM_F_MULTI flag. e.g. netlink_dump_done(),
> devlink_dpipe_{tables, entries, headers}_fill().
> 
> But from rfc3549[1]:
> 
>    [...] For multipart
>    messages, the first and all following headers have the NLM_F_MULTI
>    Netlink header flag set, except for the last header which has the
>    Netlink header type NLMSG_DONE.
> 
> What I understand is the last nlmsghdr(NLMSG_DONE message) doesn't need to
> have NLM_F_MULTI flag. Am I missing something?
> 
> [1] https://www.rfc-editor.org/rfc/rfc3549.html#section-2.3.2

Looks like you're right, we seem to fairly consistently set it.
Yet another thing in Netlink we defined and then used differently?
In practice it likely does not matter, I'd think.