2011/1/22 Mahesh Bandewar [off-list ref]:

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.

[...]

If this is going to be a flag, then maybe you could look at my ethtool
unification
series
http://marc.info/?l=linux-netdev&m=129573447816532&w=3
and integrate it there?

On the other hand, if this is going to be driver-specific value, then
you should use ethtool_get_value() and ethtool_set_value() instead of
making yet another copy
(linke eg. ETHTOOL_SMSGLVL).

Best Regards,
Michał Mirosław