linux-kernel - Re: [PATCH v8 05/12] media: Entity use count

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Message-Id: <201102041419.19916.hverkuil@xs4all.nl>
Date:	Fri, 4 Feb 2011 14:19:19 +0100
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Sakari Ailus <sakari.ailus@...well.research.nokia.com>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org, broonie@...nsource.wolfsonmicro.com,
	clemens@...isch.de
Subject: Re: [PATCH v8 05/12] media: Entity use count

On Friday, February 04, 2011 13:34:02 Sakari Ailus wrote:
> Hi,
> 
> And many thanks for the comments!
> 
> Hans Verkuil wrote:
> ...
> >> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> >> index b82f824..114541a 100644
> >> --- a/include/media/media-entity.h
> >> +++ b/include/media/media-entity.h
> >> @@ -81,6 +81,8 @@ struct media_entity {
> >>  	struct media_pad *pads;		/* Pads array (num_pads elements) */
> >>  	struct media_link *links;	/* Links array (max_links elements)*/
> >>  
> >> +	int use_count;			/* Use count for the entity. */
> > 
> > Isn't unsigned better?
> 
> Could be. The result, though, will be slightly more difficult checking
> for bad use count --- which always is a driver bug.
> 
> me->use_count += change;
> WARN_ON(me->use_count < 0);
> 
> we must do something like this:
> 
> if (change < 0)
> 	WARN_ON(me->use_count < (unsigned)-change);
> me->use_count += change;
> 
> I'd perhaps also go with unsigned int; the choice for signed was made
> mainly since the above check and with signed int the check was more trivial.

I saw this WARN_ON as well. I think there is a good reason for that WARN_ON,
but I think a comment in the header explaining why it is an int will be
useful. If I trip over it, then others will as well :-)

Regards,

	Hans

> 
> Regards,
> 
> 

-- 
Hans Verkuil - video4linux developer - sponsored by Cisco
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