netdev - Re: [PATCH net-next v5] rtnetlink: add new RTM

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Message-ID: <1461060543.2766.20.camel@sipsolutions.net>
Date:	Tue, 19 Apr 2016 12:09:03 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com
Cc:	roopa@...ulusnetworks.com, netdev@...r.kernel.org,
	jhs@...atatu.com, tgraf@...g.ch, nicolas.dichtel@...nd.com,
	Emmanuel Grumbach <egrumbach@...il.com>
Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to
 dump link stats

On Mon, 2016-04-18 at 23:52 -0400, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Mon, 18 Apr 2016 21:48:51 -0400 (EDT)
> 
> > I think the time has probably come to have a new netlink attribute
> > format that doesn't have this multi-decade old problem.
>  ...
> 
> Scratch this whole idea, I think the padding attribute works a lot
> better and is backwards compatible with every properly written
> netlink application.

This talk about attribute flags reminded me about something else.

At netconf, we talked about how awkward it can be that one doesn't know
if an attribute was accepted by the kernel or simply ignored because
it's not supported (older kernel version).

I considered (and Emmanuel has started to cook up a patch for it)
adding a flag here meaning "reject if not parsed" (or so).

Now, I realize that with all the existing netlink commands one can't
actually rely on that (since it requires some infrastructure), but new
commands in existing families and also entirely new generic netlink
families would allow let userspace rely on such a thing.

Thoughts?

johannes