Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to dump link stats

From: Johannes Berg <[email-masked]>
Date: Tue, 19 Apr 2016 21:41:41 +0200

On Tue, 2016-04-19 at 14:23 -0400, David Miller wrote:
> 
> I like this nlattr flag idea, it's opt-in and any tool can be updated
> to use the new facility.

Right.

> I'd be willing the backport the nlattr flag bit change to all stable
> releases as well.

I'm not really convinced that helps much - tools still can't really
rely on the kernel supporting it.

One thing that might work is that a tool might say it only wants to
support kernels that have this change (assuming we backport it to
enough kernels etc.); in that case the tool could add some absolutely
must-have information (like the IFINDEX or whatever, depends on the
command) with the new flag, this would get rejected since unpatched
kernels wouldn't understand the flag and wouldn't find that must-have
information.

Nevertheless, I think it's most reliable with new netlink commands that
are known to be available only on kernels understand and treating the
flag correctly.

johannes