linux-kernel - Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

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Message-ID: <20130128131622.GA1783@avionic-0098.mockup.avionic-design.de>
Date:	Mon, 28 Jan 2013 14:16:23 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Florian Vaussard <florian.vaussard@...l.ch>
Cc:	Peter Ujfalusi <peter.ujfalusi@...com>,
	Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

On Mon, Jan 28, 2013 at 11:57:39AM +0100, Florian Vaussard wrote:
> Le 28/01/2013 10:57, Thierry Reding a écrit :
> >On Mon, Jan 28, 2013 at 10:36:07AM +0100, Florian Vaussard wrote:
> >>Hello,
> >>
> >>Le 28/01/2013 09:45, Peter Ujfalusi a écrit :
> >>>hi Thierry,
> >>>
> >>>On 01/26/2013 06:40 AM, Thierry Reding wrote:
> >[...]
> >>>>>+{
> >>>>>+	return pwm->chip->can_sleep;
> >>>>>+}
> >>>>>+EXPORT_SYMBOL_GPL(pwm_cansleep);
> >>>>
> >>>>Would it make sense to check for NULL pointers here? I guess that
> >>>>passing NULL into the function could be considered a programming error
> >>>>and an oops would be okay, but in that case there's no point in making
> >>>>the function return an int. Also see my next comment.
> >>>
> >>>While it is unlikely to happen it is better to be safe, something like this
> >>>will do:
> >>>
> >>>return pwm ? pwm->chip->can_sleep : 0;
> >>>
> >>
> >>Ok. And what about:
> >>
> >>BUG_ON(pwm == NULL);
> >>return pwm->chip->can_sleep;
> >
> >I don't think we need that. In case pwm == NULL, dereferencing it will
> >oops anyway. So either we make it safe and return an error code, or we
> >let it oops without explicit BUG_ON().
> >
> 
> Calling this function with a NULL pointer is a programming error, so there
> is no error codes for such errors.

You could return -EINVAL if pwm == NULL.

> I propose to return bool, and let it oops if such case happens.

My point was that it will oops even if you don't use BUG_ON() so there
isn't so much point in using it explicitly.

Thierry

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