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

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Date:	Fri, 22 May 2015 03:46:51 +0300
From:	Vladimir Zapolskiy <vz@...ia.com>
To:	Tejun Heo <tj@...nel.org>
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

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.

> Thanks.
> 

--
With best wishes,
Vladimir
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