Re: [PATCHv3 net-next] ipv6: allow routes to be configured with expire values

[David Miller <davem@davemloft.net>]

From: Dan Williams <dcbw@redhat.com>
Date: Wed, 16 Dec 2015 11:03:52 -0600

> On Wed, 2015-12-16 at 17:50 +0800, Xin Long wrote:
>> Add the support for adding expire value to routes,  requested by
>> Tom Gundersen <teg@jklm.no> for systemd-networkd, and NetworkManager
>> wants it too.
>> 
>> implement it by adding the new RTNETLINK attribute RTA_EXPIRES.
> 
> Could you also add bits to send RTA_EXPIRES back to userspace in the
> route dump in rt6_fill_node(), so that userspace can figure out when
> RTA_EXPIRES is supported or not?
> 
> (obviously having it there isn't foolproof as if there are no routes on
> the system yet userspace can't figure out support, but it's better than
> nothing...)

That brings up an interesting issue, and I do not agree that we should
publish the value for the purpose of determining if the kernel supports
it or not.

We need to come up with a policy for handling unknown attributes
because what we do now doesn't work.

I'm almost positive that the right thing to do is to unilaterally
making nlmsg_parse() error out on out-of-range attribute type numbers,
and then backport that to all -stable branches.