From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [patch net-next 0/4] net: allow to change carrier from
 userspace
Date: Wed, 12 Dec 2012 10:36:32 -0800
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To: Jiri Pirko <jiri@resnulli.us>
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On Wed, 12 Dec 2012 19:25:56 +0100
Jiri Pirko <jiri@resnulli.us> wrote:

> Wed, Dec 12, 2012 at 07:12:08PM CET, shemminger@vyatta.com wrote:
> >On Wed, 12 Dec 2012 19:10:17 +0100
> >Jiri Pirko <jiri@resnulli.us> wrote:
> >
> >> ># ip li show dev dummy0
> >> >12: dummy0: <NO-CARRIER,BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state DORMANT mode DORMANT   
> >> 
> >> if you mean this "NO-CARRIER"
> >> it has no direct relation with netif_carrier_ok().
> >
> >It is the same value (IFF_RUNNING) that is visible from user space.
> 
> static inline bool netif_carrier_ok(const struct net_device *dev)
> {
> 	        return !test_bit(__LINK_STATE_NOCARRIER, &dev->state);
> }
> 
> So netif_carrier[ok/on/off] are working with on __LINK_STATE_NOCARRIER
> bit. Not with IFF_RUNNING flag.

What is the code path that you are worried about netif_carrier_ok being set or clear?
The interaction here is complex, and right now LINK_STATE_NOCARRIER is purely
controlled by the driver, your patch changes that, but before acking I want
to make sure why it is required.