netdev - Re: RTM_NEWLINK not received by application when connecting multiple devices simultaneously

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Message-ID: <20120419075452.379f711b@s6510.linuxnetplumber.net>
Date:	Thu, 19 Apr 2012 07:54:52 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Kristian Evensen <kristian.evensen@...il.com>,
	netdev@...r.kernel.org
Subject: Re: RTM_NEWLINK not received by application when connecting
 multiple devices simultaneously

On Thu, 19 Apr 2012 07:26:22 -0700
Ben Greear <greearb@...delatech.com> wrote:

> On 04/19/2012 04:44 AM, Kristian Evensen wrote:
> > Hello,
> 
> > The application works as intended when I connect interfaces one by
> > one. However, if I connect two interfaces "simultaneously", the
> > RTM_NEWLINK message for one of the interfaces is sometimes not
> > received. Nothing arrives at the handle. It seems to be random which
> > RTM_NEWLINK actually arrives. I have only been able to recreate this
> > problem when connecting two USB 3G modems and automatically dialing
> > the ISP, but I assume it would happen with other technologies as well.
> > What puzzles me, is that both RTM_NEWLINK messages are seen by for
> > example ip monitor. This has led me to conclusion that there is a bug
> > in my application, and my question is therefore, are there any common
> > mistakes one can make or things to forget that would cause a message
> > to get lost or not be received, or does anyone have any tips on where
> > I can start looking?
> 
> Multiple netlink msgs can be received in each read of a netlink
> socket.  Maybe you are only processing the first one?

I recommend using the libmnl library instead of the older
libnetlink. The code is cleaner and it handles error cases better.
In libmnl there is a callback interface for parsing
netlink messages.
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