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

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Date:	Thu, 6 Jan 2011 16:47:04 -0800
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Jeff Garzik <jeff@...zik.org>,
	Stephen Hemminger <shemminger@...tta.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 Thu, Jan 6, 2011 at 2:13 PM, Ben Hutchings <bhutchings@...arflare.com> wrote:
> On Wed, 2011-01-05 at 11:22 -0500, Jeff Garzik wrote:
>> On 01/04/2011 08:21 PM, Ben Hutchings 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 doesn't have to be.  As Stephen guessed, [GS]FLAGS are basically
>> common flags -- as differentiated from private,
>> driver-specific/hardware-specific flags.
>
> Well, that would allow the patch to be simplified quite a bit. :-)

Ben, Are you suggesting to use ETH_FLAG_LOOPBACK instead of
ETHTOOL_{G|S}LOOPBACK flags?

Thanks,
--mahesh..

>
> Ben.
>
> From: Ben Hutchings <bhutchings@...arflare.com>
> Subject: [PATCH net-2.6] ethtool: Define ETH_FLAG_LOOPBACK
> Date: Thu, 6 Jan 2011 22:10:55 +0000
>
> Mahesh Bandewar <maheshb@...gle.com> requested this, writing:
>
> 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.
>
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
>
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -309,6 +309,7 @@ struct ethtool_perm_addr {
>  * flag differs from the read-only value.
>  */
>  enum ethtool_flags {
> +       ETH_FLAG_LOOPBACK       = (1 << 2),     /* Host-side loopback enabled */
>        ETH_FLAG_TXVLAN         = (1 << 7),     /* TX VLAN offload enabled */
>        ETH_FLAG_RXVLAN         = (1 << 8),     /* RX VLAN offload enabled */
>        ETH_FLAG_LRO            = (1 << 15),    /* LRO is enabled */
> ---
>
> --
> Ben Hutchings, Senior Software Engineer, Solarflare Communications
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
>
>
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