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

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Message-ID: <AANLkTim6VUBkT9NRX3jcufpXatNb9RLJbKZYCkVarFuX@mail.gmail.com>
Date:	Tue, 4 Jan 2011 17:39:23 -0800
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Ben Hutchings <bhutchings@...arflare.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 Tue, Jan 4, 2011 at 5:29 PM, Stephen Hemminger <shemminger@...tta.com> wrote:
> 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.
> --
>

This is not merely getting / setting flags but involves invoking a
method from the driver(s). If done this way; the code in
ethtool_op_set_flags() will have to be special-cased to handle this
flag which (I think) would not be clean.
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