netdev - Trying to implement secondary loopback

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Message-ID: <513DA321.8070904@hhi.fraunhofer.de>
Date:	Mon, 11 Mar 2013 10:25:53 +0100
From:	Thomas Martitz <thomas.martitz@....fraunhofer.de>
To:	netdev@...r.kernel.org
Subject: Trying to implement secondary loopback

Hello folks,

I'm Thomas Martitz, working on my Master Thesis: an Ethernet NIC. As 
part of my work I want to develop a custom loopback interface (for 
testing purposes).

However I'm facing a problem: It doesn't appear to be possible for a 
second loopback device to exist. Even when copying (and module'ifying) 
drivers/net/loopback.c the resulting device doesn't behave like the 
standard lo interface.

After examing the code I found this line (in loopback_net_init()):

loopback.c:206         net->loopback_dev = dev;

This suggests that the current network namespace can only have one 
loopback interface. And indeed after modifying my custom interface to 
include this particular line it begins to work, but obviously at the 
same time the standard lo interface stops working.

So my questions are:
* Is this on purpse/expected?
* Is there anyway around it so that I can have a custom loopback 
interface without touching lo's functionality.

Many thanks in advance.

Best regards.

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