From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Jones <davej@redhat.com>
Subject: Re: dummy file read periodically for external USB Hard Disk
Date: Mon, 7 Jul 2014 23:17:04 -0400
Message-ID: <20140708031704.GA15698@redhat.com>
References: <CANudz+tNyzco0hAm0WEqE0X=MsjF=Ykmcs0jZf1p-XF7Zt+JsA@mail.gmail.com>
 <20140708130127.0f29a46f@notabene.brown>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: loody <miloody@gmail.com>,
	Linux-FSDevel <linux-fsdevel@vger.kernel.org>
To: NeilBrown <neilb@suse.de>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:31164 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751245AbaGHDRQ (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
	Mon, 7 Jul 2014 23:17:16 -0400
Content-Disposition: inline
In-Reply-To: <20140708130127.0f29a46f@notabene.brown>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Tue, Jul 08, 2014 at 01:01:27PM +1000, NeilBrown wrote:
 > On Mon, 7 Jul 2014 22:42:29 +0800 loody <miloody@gmail.com> wrote:
 > 
 > > hi all:
 > >     we met a USB Hard Disk that will go to suspend if host stop
 > > sending scsi read command over 5mins.
 > >     To save the IO, kernel will keep the file in page cache as much as
 > > he can and under this circumstances, the read command may disappear
 > > for a while longer enough to cause the device suspend.
 > > 
 > >     is there any kernel config or module parameter can do the dummy
 > > read periodically, even the sector 0 (MBR) is fine.
 > >     or is there any kernel api I can use to read sector 0(MBR) maybe
 > > every 4mins?
 > 
 > Open the device with O_DIRECT and read a block every 4 minutes.
 > That should keep it awake.

modifying /sys/module/usbcore/parameters/autosuspend might also have the
desired effect without the need for periodic reads.

	Dave