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

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Date:	Tue, 4 Jan 2011 17:29:39 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Mahesh Bandewar <maheshb@...gle.com>,
	David Miller <davem@...emloft.net>,
	Laurent Chavey <chavey@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] net: Allow ethtool to set interface in loopback
 mode.

On Wed, 05 Jan 2011 01:21:44 +0000
Ben Hutchings <bhutchings@...arflare.com> wrote:

> On Tue, 2011-01-04 at 16:36 -0800, Stephen Hemminger wrote:
> > On Tue,  4 Jan 2011 16:30:01 -0800
> > Mahesh Bandewar <maheshb@...gle.com> wrote:
> > 
> > > This patch enables ethtool to set the loopback mode on a given interface.
> > > By configuring the interface in loopback mode in conjunction with a policy
> > > route / rule, a userland application can stress the egress / ingress path
> > > exposing the flows of the change in progress and potentially help developer(s)
> > > understand the impact of those changes without even sending a packet out
> > > on the network.
> > > 
> > > Following set of commands illustrates one such example -
> > > 	a) ip -4 addr add 192.168.1.1/24 dev eth1
> > > 	b) ip -4 rule add from all iif eth1 lookup 250
> > > 	c) ip -4 route add local 0/0 dev lo proto kernel scope host table 250
> > > 	d) arp -Ds 192.168.1.100 eth1
> > > 	e) arp -Ds 192.168.1.200 eth1
> > > 	f) sysctl -w net.ipv4.ip_nonlocal_bind=1
> > > 	g) sysctl -w net.ipv4.conf.all.accept_local=1
> > > 	# Assuming that the machine has 8 cores
> > > 	h) taskset 000f netserver -L 192.168.1.200
> > > 	i) taskset 00f0 netperf -t TCP_CRR -L 192.168.1.100 -H 192.168.1.200 -l 30
> > > 
> > > Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
> > > Reviewed-by: Ben Hutchings <bhutchings@...arflare.com>
> > 
> > Since this is a boolean it SHOULD go into ethtool_flags rather than
> > being a high level operation.
> 
> It could do, but I though ETHTOOL_{G,S}FLAGS were intended for
> controlling offload features.

It just seems the number of hooks keeps growing which takes more space
and increases complexity.

There was some talk about changing GRO/TSO/UFO .. to be bits in FLAGS
but not sure how far along that is.
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