netdev - Re: Question: should local address be expired when updating PMTU?

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Message-ID: <20150330103210.GI3311@secunet.com>
Date:	Mon, 30 Mar 2015 12:32:12 +0200
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	shengyong <shengyong1@...wei.com>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<yangyingliang@...wei.com>, <hannes@...hat.com>
Subject: Re: Question: should local address be expired when updating PMTU?

On Fri, Feb 27, 2015 at 10:37:46AM +0800, shengyong wrote:
> 
> 
> 在 2015/2/5 15:21, Steffen Klassert 写道:
> > On Wed, Feb 04, 2015 at 09:59:54AM +0800, shengyong wrote:
> >>
> >> Sorry, the later. I test it on 3.10-stable. It can fix this problem. So maybe this is a bug?
> > 
> > Yes, it's a bug.
> > 
> >> And the 3 approaches (different flags are used: RTF_LOCAL, IFF_LOOPBACK and RTF_CACHE) in
> >> these mails can fix the expire of local address. I'm confused about these flags:
> >> * RTF_LOCAL: the entries of local address, like address binded to the native NIC
> >> * RTF_CACHE: all cached entries
> >> * IFF_LOOPBACK: this is a device-related flag, which has the same meaning as RTF_LOCAL
> >>
> >> Am I right? If so, I think RTF_LOCAL is appropriate, because we just want entries of local
> >> addresses to be not expired and we don't care other entries (I think if they get expired,
> >> a neigh discovery could find them back).
> > 
> > It is not the address that expires, it is the learned PMTU value that
> > expires. If we delete an uncached route, nothing will bring it back
> > unless you readd it manually.
> > 
> > We need to ensure that all routes that can learn something what
> > expires are cached. This means that we clone the inserted route
> > when it is used for the first time. The learned values are stored
> > at this cloned route. If the learned value expires, the clone is
> > deleted. The original route remains in the fib tree and can be
> > still looked up.
> > 
> > The problem is, that we currently don't cache/clone host routes.
> > So if a host route learns something that expires, the original
> > route is removed from the fib tree and we loose connectivity
> > to that host. We don't cache host routes because some of them
> > (the local ones) are automatically added with metric 0.
> > If we try to cache such a route, the clone will be identical
> > to the original route and we fail to insert it to the fib tree.
> > 
> > So we need to adjust the caching to all routes that actually can
> > learn something and leave out only those that can not.
> > 
> > I'll send a patchset that should fix this at the beginning of the
> > next week.
> Hi, Steffen
> Is this patchset ready? It seems that I didn't find it in the mainling
> list. If it is ready, I can test it to see if it solves the problem I
> met :)

I finally end up with a patchset that passed all your testcases.
I'll send it in reply to this mail, please test it.

Thanks!
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