linux-kernel - Re: [PATCH] fs: sysfs: don't pass count == 0 to bin file readers

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Date:	Sun, 24 May 2015 20:07:09 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vladimir Zapolskiy <vz@...ia.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: sysfs: don't pass count == 0 to bin file readers

On Fri, May 22, 2015 at 03:46:51AM +0300, Vladimir Zapolskiy wrote:
> Hello Tejun,
> 
> On 22.05.2015 02:26, Tejun Heo wrote:
> > Hello, Vladimir.
> > 
> > On Fri, May 22, 2015 at 02:04:31AM +0300, Vladimir Zapolskiy wrote:
> >> But "!size" is a special case,
> >>
> >> 	if (!count || pos >= size)
> >> 		return 0;
> >>
> >> seems to be incorrect in case of !size ===> (pos >= size) == true.
> > 
> > Hmmm... Why is that wrong tho?  If size is zero and pos is zero,
> > there's nothing to do, no?
> 
> positive size value in the context means the fixed exact length of the
> file and if size == 0, then it represents some undefined size, often
> dynamic in runtime. So, if size is zero and pos is zero it stands for
> reading from the beginning of the file as many bytes as allowed by
> battr->read() realization. This special case is utilized by quite many
> bin_attribute users, probably more than half of them set .size to 0.

Ah, right, I completely forgot about that.  Please feel free to add

 Acked-by: Tejun Heo <tj@...nel.org>

to the original patch.

Thanks for the patience.

-- 
tejun
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