linux-kernel - Re: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f

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Message-ID: <873a24mc3i.fsf@devron.myhome.or.jp>
Date:	Mon, 18 Jan 2010 10:32:49 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>, Nick Piggin <npiggin@...e.de>,
	Andi Kleen <andi@...stfloor.org>,
	David Howells <dhowells@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	<linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f_pos

OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> writes:

>>> Um... How do lseek() work? It sounds like to violate error code range.
>>
>> This is for read-write. As far as I know, 
>>   - generic_file_llseek,
>>   - default_llseek
>>   - no_llseek
>>
>> doesn't call this function. 
>
> It seems to allow to set negative value to ->f_pos, right? So, lseek()
> returns (uses) it?

BTW, another concern by negative "pos" value is, the following like code

	pos >> shift_bits

it will break the above. So, I think it should be checked if not yet.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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