linux-kernel - Re: [RFC PATCH] sysfs: refill attribute buffer when reading from offset 0

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Date:	Mon, 07 Apr 2008 21:43:06 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Dan Williams <dan.j.williams@...el.com>, gregkh@...e.de,
	linux-kernel@...r.kernel.org, neilb@...e.de
Subject: Re: [RFC PATCH] sysfs: refill attribute buffer when reading from
 offset 0

Hello,

Andrew Morton wrote:
>>  The application for this change is to allow a userspace
>> RAID metadata handler to check the state of an array without causing any
>> memory allocations.  Thus not causing writeback to a raid array that might
>> be blocked waiting for userspace to take action.
> 
> Although that sounds like a rather, umm, optimistic application.  I guess
> if everything's mlocked you might get lucky.
> 
>> Cc: NeilBrown <neilb@...e.de>
>> Cc: Tejun Heo <htejun@...il.com>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Acked-by: Tejun Heo <htejun@...il.com>

> Has this been tested with pread()?  That should work - doing an lseek+read
> is plain dopey.
> 
> Can we now remove need_read_fill?  Not if we want to support
> open+lseek+read, I guess - this initial read might not be at offset
> zero.

Heh.. needs_read_fill is set after read and poll regardless of file pos 
and I bet there are applications depending on it.  :-(

-- 
tejun
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