netdev - Re: notifications of interfaces going down/up/being created/destroyed?

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Message-ID: <20150330205934.GA29542@f1.synalogic.ca>
Date:	Mon, 30 Mar 2015 13:59:34 -0700
From:	Benjamin Poirier <benjamin.poirier@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: notifications of interfaces going down/up/being
 created/destroyed?

On 2015/03/28 09:37, Dave Taht wrote:
> is there an asynchronous way to register for a notification of an
> interface going down/up?

Look at what `ip monitor` is doing.

> 
> ---------- Forwarded message ----------
> From: Juliusz Chroboczek <jch@....univ-paris-diderot.fr>
> Date: Sat, Mar 28, 2015 at 9:30 AM
> Subject: Re: [Babel-users] Looping in EAGAIN
> To: Dave Taht <dave.taht@...il.com>
> Cc: Simon Kelley <simon@...kelleys.org.uk>,
> "babel-users@...ts.alioth.debian.org"
> <babel-users@...ts.alioth.debian.org>
> 
> 
> > Say wlan0 vanishes. All the routes going out that interface are no
> > longer valid, but from what I understood of this patch, it will loop for
> > a while, then give up.
> 
> If wlan0 vanishes, this will be recognised the next time check_interfaces
> is run, and all neighbours visible through wlan0 will be flushed.
> 
> The issue we're having is a race condition -- if wlan0 goes down and then
> back up before we run check_interfaces, and the IP addresses don't change,
> then check_interfaces will not notice the transition, and Babel will think
> that its routes through wlan0 are still up -- end you end up with a FIB
> that is not a subset of the RIB.  Ouch.
> 
> So it might be a good idea to run check_interfaces early when we get
> EAGAIN, but I'm not sure what consequences it might have -- EAGAIN can
> also happen when we're under load, and we'd rather not be repeatedly
> scanning our interfaces in that case.
> 
> It would be better to get async notifications from the kernel about
> interfaces going down.
> 
> > Not clear to me if this would happen for 4 hello intervals before the
> > interface is recognised as gone?
> 
> No, the hellos are used to notice vanishing neighbours, not vanishing
> interfaces.  That's a completely different mechanism.
> 
> -- Juliusz
> 
> 
> -- 
> Dave Täht
> Let's make wifi fast, less jittery and reliable again!
> 
> https://plus.google.com/u/0/107942175615993706558/posts/TVX3o84jjmb
> --
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