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

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Message-Id: <20100118104913.66c8d90c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 18 Jan 2010 10:49:13 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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

On Mon, 18 Jan 2010 10:32:49 +0900
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> wrote:

> 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.

Where do we check ?

FMODE_NEG_OFFSET is just used by /dev/mem and /proc/<pid>/mem. And I don't
think there are no additonal users. So, I myself don't have has such concerns...


Thanks,
-Kame

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