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Date: Mon, 18 Jan 2010 10:49:13 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Al Viro <viro@zeniv.linux.org.uk>,
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       David Howells <dhowells@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
       <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing
 negative f_pos
Message-Id: <20100118104913.66c8d90c.kamezawa.hiroyu@jp.fujitsu.com>
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On Mon, 18 Jan 2010 10:32:49 +0900
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:

> OGAWA Hirofumi <hirofumi@mail.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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