linux-kernel - Re: Network link detection

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Date:	Thu, 3 Mar 2011 21:03:29 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Nico Schümann <dev@...o22.de>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Network link detection

On Thu, 3 Mar 2011, Nico Schümann wrote:

> Dear kernel developers,
> 
> currently I'm looking for a way to find out whether a network link went 
> down or up. Of course there is mii-tool, which can watch devices, too.
> 
> So for now, I created a small program that polls the MII_LINK_OK
> flag with the SIOCGMIIREG ioctl - the same thing that mii-tools does. 
> But polling that often for a link change that occurs maybe once in a 
> month sounds like waste of energy.
> 
> Unfortunately, I was not able to find out a way to be notified about 
> link status changes asynchronously. Is there a way? I'm looking for 
> something like "inotify for link states".
> 
I guess you could use inotify to keep an eye on the 'carrier' file in 
sysfs (for example, from my system; 
/sys/devices/pci0000:00/0000:00:19.0/net/eth0/carrier )
That file will contain "0" if there is no link and "1" if there is a link.

-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
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