netdev - Re: [PATCH v2] ethtool : Allow ethtool to set interface in loopback mode.

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Message-Id: <20101204203348.cf4fc883.billfink@mindspring.com>
Date:	Sat, 4 Dec 2010 20:33:48 -0500
From:	Bill Fink <billfink@...dspring.com>
To:	David Lamparter <equinox@...c24.net>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Mahesh Bandewar <maheshb@...gle.com>,
	linux-netdev <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH v2] ethtool : Allow ethtool to set interface in loopback
 mode.

On Fri, 3 Dec 2010, David Lamparter wrote:

> On Fri, Dec 03, 2010 at 04:33:34PM +0000, Ben Hutchings wrote:
> > On Fri, 2010-12-03 at 17:03 +0100, David Lamparter wrote:
> > > On Thu, Dec 02, 2010 at 02:35:51PM -0800, Mahesh Bandewar wrote:
> > > > This patch adds -L command-line option to switch loopback mode on/off
> > > > and -l option to display current loopback mode on a specified interface.
> > > [...]
> > > > +.A1 on off
> > > > +Switches loopback mode
> > > > +.B on
> > > > +or
> > > > +.B off
> > > 
> > > What about devices that support different kinds of loopback, like MAC
> > > loopback & PHY loopback? (No idea if we have kernel support for this
> > > either...)
> > 
> > That distinction is useful for diagnostic purposes, but drivers can
> > already cover those different loopback modes in self-test.  The
> > motivation for this feature is testing data path behaviour, and Mahesh
> > has specified that loopback should be enabled as near as possible to the
> > host.
> 
> Ah, good enough. Thanks.

Perhaps in the future it could be extended, if desired,
to something like:

	loopback=0	disabled
	loopback=1	driver loopback nearest host
	loopback=2	driver loopback nearest network

Both types of loopback could be useful for different purposes.

					-Bill
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