Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756281AbYKDUNY (ORCPT ); Tue, 4 Nov 2008 15:13:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753799AbYKDUNQ (ORCPT ); Tue, 4 Nov 2008 15:13:16 -0500 Received: from nf-out-0910.google.com ([64.233.182.187]:10292 "EHLO nf-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753290AbYKDUNQ (ORCPT ); Tue, 4 Nov 2008 15:13:16 -0500 Message-ID: Date: Tue, 4 Nov 2008 21:13:10 +0100 From: "Kay Sievers" To: "Pavel Machek" Subject: Re: data corruption: revalidating a (removable) hdd/flash on re-insert Cc: "Michael Tokarev" , "Kernel Mailing List" In-Reply-To: <20081104195728.GC5862@ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <490B2659.9010304@msgid.tls.msk.ru> <20081104195728.GC5862@ucw.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2262 Lines: 63 On Tue, Nov 4, 2008 at 20:57, Pavel Machek wrote: > On Fri 2008-10-31 17:10:26, Kay Sievers wrote: >> On Fri, Oct 31, 2008 at 16:38, Michael Tokarev wrote: >> > To make a long story short: is there a way to force kernel >> > to re-validate a replaced usb-connected hard drive (or a >> > flash) *automatically*? >> > >> > Because right now, the kernel does not see that the drive >> > has been replaced, and uses *some* old cached values, which >> > results in random data corruption here and there, and other >> > similar odd things. >> >> Maybe your card reader is broken. I can not reproduce this with any of >> the many readers I have. Usually a media change results in media >> revalidation with the next access to the device. You can easily >> reproduce that: >> >> Insert the media, and force a validation: >> $ touch /dev/sdb >> >> Start logging of the kernel uevents to the console: >> $ udevadm monitor --kernel & >> >> Access the device: >> $ touch /dev/sdb >> >> Nothing should happen, as the reader/kernel knows it is still valid. >> >> Now remove the media and insert it immediately again. >> >> Access the device: >> $ touch /dev/sdb >> UEVENT[1225468868.803950] change >> /devices/pci0000:00/0000:00:1d.7/usb5/5-2/5-2:1.0/host8/target8:0:0/8:0:0:0 >> (scsi) >> >> and you see the reader told to kernel (scsi unit attention) to >> revalidate the device. >> >> These events happen only when the device is accessed. That's why >> distros poll removable devices for media changes. >> >> Every access to removable media is guarded by this revalidation check. >> If you don't see these events, you should not trust this reader, and >> at least never change the media while it is connected. > > This is rather nasty data-corrupter. Sure, it is. > Could we at least blacklist > broken device, and force revalidation on each close or something like > that? What's your idea of revalidation if the hardware does not tell you? Get an md5 of the disk content? :) Kay -- 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/