linux-kernel - RE: [PATCH 01/90] staging: comedi: comedidev.h: introduce comedi_to_pci

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Date:	Thu, 19 Jul 2012 12:27:45 -0500
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	Ian Abbott <abbotti@....co.uk>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	Ian Abbott <ian.abbott@....co.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 01/90] staging: comedi: comedidev.h: introduce
 comedi_to_pci_dev() helper

On Thursday, July 19, 2012 9:32 AM, Dan Carpenter wrote:
> On Thu, Jul 19, 2012 at 11:20:52AM -0500, H Hartley Sweeten wrote:
>> On Thursday, July 19, 2012 2:23 AM, Ian Abbott wrote:
>>> That needs to be something like:
>>>
>>>	return dev->hw_dev ? to_pci_dev(dev->hw_dev) : NULL;
>> 
>> Hmm.. I'm not really sure.
>> 
>> I assumed that the container_of() macro would return NULL if the ptr passed to
>> it was NULL. But, I'm not sure how this actually unwinds for that case.
>> 
>> Greg, do you know if the NULL check is needed? It's is possible that the dev->hw_dev
>> pointer could be NULL.
>> 
>
> container_of() just does pointer math with the offset.  Since
> ->hw_dev is not the first member of the pci_dev struct then
> to_pci_dev() never returns NULL.  If you give it a NULL pointer it
> returns a bogus pointer back.

Thanks for the information.

I'll update PATCH 01/90 and repost it as v2.

Thanks,
Hartley

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