linux-kernel - Re: [PATCH v2 4/7] [PATCH 4/8] can: Driver for the SJA1000 CAN controller

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Message-ID: <20090515143927.7ba06f10@bike.lwn.net>
Date:	Fri, 15 May 2009 14:39:27 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oliver Hartkopp <oliver.hartkopp@...kswagen.de>
Subject: Re: [PATCH v2 4/7] [PATCH 4/8] can: Driver for the SJA1000 CAN
 controller

On Thu, 14 May 2009 11:03:53 +0200
Wolfgang Grandegger <wg@...ndegger.com> wrote:

> > So you're still using the "put the higher-level structure at the top so we
> > can treat it like either kind of pointer" trick.  I'd still recommend
> > against that.  Far better to do something like:
> > 
> > 	struct can_priv *canpriv = netdev_priv(dev);
> > 	struct sja_1000_priv *priv = container_of(canpriv, struct sja_1000_priv, can);
> > 
> > Of course, you can put that dance into a helper function.  
> 
> There is no way to initialize the value returned by netdev_priv() as it
> does not point to a member of struct net_device. I already commented here:
> 
>   http://marc.info/?l=linux-netdev&m=124120212106891&w=2
> 
> Have I missed something?

I'm confused.  It points to the struct can_priv that you registered at
the beginning.  Since that structure is contained within struct
sja1000_priv, you can use container_of(), as described above, to get
it.

I would probably just write something like:

static inline struct sja1000_priv *to_sja1000_priv(struct net_device *dev)
{
	return container_of(netdev_priv(dev), struct sja1000_priv, can);
}

So have *I* missed something?

jon
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