Return-Path: <linux-kernel-owner+w=401wt.eu-S1755881AbZIOILh@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755881AbZIOILh (ORCPT <rfc822;w@1wt.eu>);
	Tue, 15 Sep 2009 04:11:37 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751499AbZIOILd
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Tue, 15 Sep 2009 04:11:33 -0400
Received: from mga14.intel.com ([143.182.124.37]:30721 "EHLO mga14.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751050AbZIOILb (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 15 Sep 2009 04:11:31 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="4.44,388,1249282800"; 
   d="scan'208";a="187714440"
Date: Tue, 15 Sep 2009 16:11:07 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
       Andrew Morton <akpm@linux-foundation.org>,
       "mtosatti@redhat.com" <mtosatti@redhat.com>,
       "gregkh@suse.de" <gregkh@suse.de>,
       "broonie@opensource.wolfsonmicro.com" 
	<broonie@opensource.wolfsonmicro.com>,
       "johannes@sipsolutions.net" <johannes@sipsolutions.net>,
       "avi@qumranet.com" <avi@qumranet.com>,
       "andi@firstfloor.org" <andi@firstfloor.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Question: how to handle too big f_pos Re: [PATCH] devmem:
	handle partial kmem write/read
Message-ID: <20090915081107.GA3625@localhost>
References: <20090914032901.GA16189@localhost> <20090915165852.032d164f.kamezawa.hiroyu@jp.fujitsu.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090915165852.032d164f.kamezawa.hiroyu@jp.fujitsu.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 3483
Lines: 120

Good catch, Kame!

FYI mmap is OK. I succeeded in reading this address via kmem:

        ffffffff81723880 D modprobe_path

Thanks,
Fengguang

On Tue, Sep 15, 2009 at 03:58:52PM +0800, KAMEZAWA Hiroyuki wrote:
> I'm writing a patch against /dev/kmem...I found a problem.
> 
> /dev/kmem (and /proc/<pid>/mem) puts virtual addres to f->f_pos.
> 
> And, f->f_pos is loff_t .... signed value (not unsigned)
> 
> Then, this check
> rw_verify_area(READ, file, pos, count);
> =>
>         pos = *ppos;
>         if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
>                 return retval;
> 	
> always returns -EINVAL when I read /dev/kmem's valid address.
> 
> Then, how should I do for read /dev/kmem ? Any idea ?
> (Added Al Viro to CC:)
> 
> What I'm really afraid of is /proc/<pid>/mem. IIUC, it's used by gdb to snoop
> memory, (for example, at gcore).
> I think gdb uses ptrace if it fails to read /proc/<pid>/mem but...it's deadly
> slow.
> 
> Thanks,
> -Kame
> 
> p.s. no problems in /proc/kcore..its offset is not bare addresss.
> 
> 
> 
> 
> 
> On Mon, 14 Sep 2009 11:29:01 +0800
> Wu Fengguang <fengguang.wu@intel.com> wrote:
> 
> > Current vwrite silently ignores vwrite() to vmap holes.
> > Better behavior should be stop the write and return
> > on such holes.
> > 
> > Also return on partial read, which may happen in future
> > (eg. hit hwpoison pages).
> > 
> > CC: Andi Kleen <andi@firstfloor.org>
> > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> > ---
> >  drivers/char/mem.c |   30 ++++++++++++++++++------------
> >  1 file changed, 18 insertions(+), 12 deletions(-)
> > 
> > --- linux-mm.orig/drivers/char/mem.c	2009-09-14 10:59:50.000000000 +0800
> > +++ linux-mm/drivers/char/mem.c	2009-09-14 11:06:25.000000000 +0800
> > @@ -444,18 +444,22 @@ static ssize_t read_kmem(struct file *fi
> >  		if (!kbuf)
> >  			return -ENOMEM;
> >  		while (count > 0) {
> > +			unsigned long n;
> > +
> >  			sz = size_inside_page(p, count);
> > -			sz = vread(kbuf, (char *)p, sz);
> > -			if (!sz)
> > +			n = vread(kbuf, (char *)p, sz);
> > +			if (!n)
> >  				break;
> > -			if (copy_to_user(buf, kbuf, sz)) {
> > +			if (copy_to_user(buf, kbuf, n)) {
> >  				free_page((unsigned long)kbuf);
> >  				return -EFAULT;
> >  			}
> > -			count -= sz;
> > -			buf += sz;
> > -			read += sz;
> > -			p += sz;
> > +			count -= n;
> > +			buf += n;
> > +			read += n;
> > +			p += n;
> > +			if (n < sz)
> > +				break;
> >  		}
> >  		free_page((unsigned long)kbuf);
> >  	}
> > @@ -551,11 +555,13 @@ static ssize_t write_kmem(struct file * 
> >  				free_page((unsigned long)kbuf);
> >  				return -EFAULT;
> >  			}
> > -			sz = vwrite(kbuf, (char *)p, sz);
> > -			count -= sz;
> > -			buf += sz;
> > -			virtr += sz;
> > -			p += sz;
> > +			n = vwrite(kbuf, (char *)p, sz);
> > +			count -= n;
> > +			buf += n;
> > +			virtr += n;
> > +			p += n;
> > +			if (n < sz)
> > +				break;
> >  		}
> >  		free_page((unsigned long)kbuf);
> >  	}
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> > 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/