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

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Message-ID: <49FB3D9B.3050704@grandegger.com>
Date:	Fri, 01 May 2009 20:21:15 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Jonathan Corbet <corbet@....net>
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oliver Hartkopp <oliver.hartkopp@...kswagen.de>
Subject: Re: [PATCH 4/8] can: Driver for the SJA1000 CAN controller

I'm now back fixing the open issues of this patch series...

Jonathan Corbet wrote:
[snip]
>> +/*
>> + * SJA1000 private data structure
>> + */
>> +struct sja1000_priv {
>> +	struct can_priv can;	/* must be the first member! */
> 
> AHA!  I knew it!
> 
> This kind of pointer trickery is fragile and dangerous, please don't do
> it.  Much better would be something like:
> 
> 	dev->priv = &dev_specific_priv->can;
> 
> Then the higher layers know they have a proper struct can_priv pointer.
> Then you can use container_of() at this level to get the outer structure
> pointer.  Much more robust and in line with normal kernel coding idiom.

Unfortunately, the "struct net_device" does not have a "priv" field. Using

	struct can_priv *can = netdev_priv(dev);
	struct sja1000_priv *sja1000 = candev_priv(dev);

instead is awkward. That's what we had at first. Any other more elegant
solution in mind?

Wolfgang.

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