netdev - Re: [PATCHv3 2/2] tg3: Allow ethtool to enable/disable loopback.

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Date:	Wed, 4 May 2011 18:05:21 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Mahesh Bandewar <maheshb@...gle.com>,
	Matt Carlson <mcarlson@...adcom.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCHv3 2/2] tg3: Allow ethtool to enable/disable loopback.

On Wed, May 04, 2011 at 08:04:08AM -0700, Stephen Hemminger wrote:
> On Wed, 4 May 2011 13:11:12 +0200
> Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:
> > On Tue, May 03, 2011 at 06:18:55PM -0700, Mahesh Bandewar wrote:
> > > This patch adds tg3_set_features() to handle loopback mode. Currently the
> > > capability is added for the devices which support internal MAC loopback mode.
> > > So when enabled, it enables internal-MAC loopback.
> > [...]
> > > diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
> > > index 7c7c9a8..46de633 100644
> > > --- a/drivers/net/tg3.c
> > > +++ b/drivers/net/tg3.c
> > > @@ -6319,6 +6319,51 @@ static u32 tg3_fix_features(struct net_device *dev, u32 features)
> > >  	return features;
> > >  }
> > >  
> > > +static int tg3_set_features(struct net_device *dev, u32 features)
> > > +{
> > > +	struct tg3 *tp = netdev_priv(dev);
> > > +	u32 cur_mode = 0;
> > > +	int err = 0;
> > > +
> > > +	if (!netif_running(dev)) {
> > > +		err = -EAGAIN;
> > > +		goto sfeatures_out;
> > > +	}
> > netdev_update_features() is not designed to handle -EAGAIN from
> > ndo_set_features callback. It might be useful to implement this
> > handling, but in this case you should just return 0 and check
> > dev->features in ndo_open callback.
> 
> EAGAIN is a bad choice of error code anyway. It implies that the
> application should retry, which in this case is not true.
> 
> This error code is used for things like flow controlled sockets where
> the application should do a select/poll and the condition will clear
> when other side has read.
> 
> Why not use ENETDOWN instead?

The "application" here is netdev_update_features() here. Whatever the
error code, it would need to be handled there.

Best Regards,
Michał Mirosław
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