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

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Message-Id: <20151217.162650.526302130376762794.davem@davemloft.net>
Date:	Thu, 17 Dec 2015 16:26:50 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	dcbw@...hat.com
Cc:	lucien.xin@...il.com, netdev@...r.kernel.org,
	hannes@...essinduktion.org
Subject: Re: [PATCHv3 net-next] ipv6: allow routes to be configured with
 expire values

From: Dan Williams <dcbw@...hat.com>
Date: Thu, 17 Dec 2015 14:23:57 -0600

> On Thu, 2015-12-17 at 15:08 -0500, David Miller wrote:
>> 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.
> 
> That said, userspace still needs to read back the EXPIRES attribute, if
> only for iproute.  The program setting RTA_EXPIRES isn't the only thing
> that wants to know about the route's details.

Agreed.

>> 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.
> 
> This works for one attribute because then userspace gets an error like
> EOPNOTSUPP or something.  But which attribute caused it?  Does
> userspace then have to retry the operation a couple times with all the
> different combinations of potentially unsupported options?
> 
> If we're going to error out on unrecognized options, I'd really like to
> see some kind of netlink features bitmap or something that positively
> indicates which options the kernel will accept.

Also agree.  But it has to be really simple and trivial so that -stable
backports are possible.
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