From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756819AbZEPG51 (ORCPT ); Sat, 16 May 2009 02:57:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753668AbZEPG5O (ORCPT ); Sat, 16 May 2009 02:57:14 -0400 Received: from mail-out.m-online.net ([212.18.0.10]:49616 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752475AbZEPG5O (ORCPT ); Sat, 16 May 2009 02:57:14 -0400 X-Auth-Info: MGPcICCeOmU5TmOzQgWKVSmQdP7W677udLt+yOsoET0= Message-ID: <4A0E63BF.9080503@grandegger.com> Date: Sat, 16 May 2009 08:57:03 +0200 From: Wolfgang Grandegger User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Jonathan Corbet CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Hartkopp Subject: Re: [PATCH v2 4/7] [PATCH 4/8] can: Driver for the SJA1000 CAN controller References: <20090512092757.048938233@denx.de> <20090512092757.756749047@denx.de> <20090513155205.4bf06c25@bike.lwn.net> <4A0BDE79.4060606@grandegger.com> <20090515143927.7ba06f10@bike.lwn.net> <4A0DDD81.4040406@grandegger.com> In-Reply-To: <4A0DDD81.4040406@grandegger.com> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wolfgang Grandegger wrote: > Jonathan Corbet wrote: >> On Thu, 14 May 2009 11:03:53 +0200 >> Wolfgang Grandegger 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? > > Furthermore, the higher layer needs to known the location of the member > "struct sja1000_priv can", e.g. by defining: > > dev->priv = &dev_specific_priv->can; > > But "struct net_device" does not have a "priv" member. netdev_priv(dev) > always points to the beginning of the private data area. See: > > http://lxr.linux.no/linux+v2.6.29/include/linux/netdevice.h#L953 I could use container_of() as you suggested, of course, if the "struct can_priv" remains the first member of "struct sja1000_priv". Would that already be an improvement? Wolfgang.