netdev - Re: [RFC PATCH v2] net: fold dev_disable_lro() into netdev_fix

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Date:	Thu, 12 May 2011 18:35:27 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Tom Herbert <therbert@...gle.com>,
	bridge@...ts.linux-foundation.org
Subject: Re: [RFC PATCH v2] net: fold dev_disable_lro() into
 netdev_fix_features()

On Thu, May 12, 2011 at 05:29:07PM +0100, Ben Hutchings wrote:
> On Thu, 2011-05-12 at 18:06 +0200, Michał Mirosław wrote:
> > This implements checks for forwarding mode in netdev_fix_features() using
> > dev->priv_flags bits. As a side effect, after device is no longer
> > forwarding it gets LRO back. This also means that user is not allowed to
> > enable LRO after device is put to forwarding mode.
> > 
> > This patch depends on removal of discrete offload setting ethtool ops.
> 
> This is nice, but:
> 
> [...]
> > --- a/net/bridge/br_if.c
> > +++ b/net/bridge/br_if.c
> > @@ -158,6 +158,8 @@ static void del_nbp(struct net_bridge_port *p)
> >  	br_netpoll_disable(p);
> >  
> >  	call_rcu(&p->rcu, destroy_nbp_rcu);
> > +
> > +	netdev_update_features(dev);
> >  }
> >  
> >  /* called with RTNL */
> > @@ -368,11 +370,9 @@ int br_add_if(struct net_bridge *br, struct net_device *dev)
> >  
> >  	dev->priv_flags |= IFF_BRIDGE_PORT;
> >  
> > -	dev_disable_lro(dev);
> > -
> >  	list_add_rcu(&p->list, &br->port_list);
> >  
> > -	netdev_update_features(br->dev);
> > +	netdev_change_features(dev);
> >  
> >  	spin_lock_bh(&br->lock);
> >  	changed_addr = br_stp_recalculate_bridge_id(br);
> Why netdev_change_features() here?  I thought that was primarily for use
> when vlan_features may have been changed.

Because this recalculates port's features and then cascades to bridge's
device. I could have written:

	netdev_update_features(dev);
	netdev_update_features(br->dev);

But that might cause redundant recalculations for br->dev (first through
notifier calls). I'll add a comment here.

> 
> [...]
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> [...]
> > @@ -5241,6 +5221,11 @@ u32 netdev_fix_features(struct net_device *dev, u32 features)
> >  		}
> >  	}
> >  
> > +	if (features & NETIF_F_LRO && dev->priv_flags & IFF_LRO_FORBIDDEN) {
> > +		netdev_info(dev, "Disabling LRO for forwarding interface.\n");
> > +		features &= NETIF_F_LRO;
> [...]
> 
> Mising '~'.

Fixed.

Best Regards,
Michał Mirosław
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