netdev - Re: [PATCH v2] net: set default_ethtool_ops in register

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Message-ID: <20130110083641.GA5637@redhat.com>
Date:	Thu, 10 Jan 2013 09:36:42 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, edumazet@...gle.com,
	greearb@...delatech.com, bjorn@...k.no,
	linux-wireless@...r.kernel.org, bhutchings@...arflare.com,
	mirqus@...il.com
Subject: Re: [PATCH v2] net: set default_ethtool_ops in register_netdevice

On Wed, Jan 09, 2013 at 11:57:38PM -0800, David Miller wrote:
> From: Stanislaw Gruszka <sgruszka@...hat.com>
> Date: Tue, 8 Jan 2013 16:38:51 +0100
> 
> > Since:
> > 
> > commit 2c60db037034d27f8c636403355d52872da92f81
> > Author: Eric Dumazet <edumazet@...gle.com>
> > Date:   Sun Sep 16 09:17:26 2012 +0000
> > 
> >     net: provide a default dev->ethtool_ops
> > 
> > wireless core does not correctly assign ethtool_ops. In order to fix
> > the problem, move assignement of default_ethtool_ops to
> > register_netdevice(). This is safe because both register_netdevice()
> > and dev_ethtool() are protected by RTNL lock.
> > 
> > Patch is besed on hint of Michał Mirosław.
> > 
> > Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
> > Cc: stable@...r.kernel.org # 3.7+
> > ---
> > v1 -> v2: change order of default_ethtool_ops initialization to avoid
> > the problem. Change the subject accordingly.
> 
> I don't understand this.  Why is the assignment of default_ethtool_ops
> at netdev allocation time not working?  Is wireless really not using
> alloc_netdev*()?

It does. This is done on individual cfg80211 drivers , i.e. on mac80211
or full mac drivers. After alloc_netdev*() call, some cfg80211 drivers
provide they own ethtool_ops, but some do not. For them, wireless core
provide generic cfg80211_ethtool_ops, which is assigned in
NETDEV_REGISTER notify call: 

	if (!dev->ethtool_ops)
		dev->ethtool_ops = &cfg80211_ethtool_ops;

But after Eric's commit, dev->ethtool_ops is no longer NULL (on cfg80211
drivers without custom ethtool_ops), but points to &default_ethtool_ops.

Stanislaw
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