Message-ID: <490B2DDF.5050809@msgid.tls.msk.ru>
Date:	Fri, 31 Oct 2008 19:10:07 +0300
From:	Michael Tokarev <mjt@....msk.ru>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
CC:	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: data corruption: revalidating a (removable) hdd/flash on re-insert

Lennart Sorensen wrote:
> On Fri, Oct 31, 2008 at 06:38:01PM +0300, 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.
>>
>> For example, I've an USB flash reader (Carry Computer Eng.,
>> Co., Ltd 6-in-1 Card Reader, but that's not really relevant).
>> Among other things it has a compact flash slot.  And I've
>> 2 differently-size CF cards.
[]
>> So at some point the kernel stopped noticing the drive
>> change in this configuration some time ago.  I can't say
>> when exactly, since I didn't use the card reader for over
>> a year, and certainly didn't try it with more than one
>> card in a row for even longer time.   It worked in the
>> past, that's for sure.  And it definitely does not work
>> (resulting in the above mess) with 2.6.25, 2.6.26 and 2.6.27.
> 
> I have had this happen with a few usb flash card readers.  My solution
> was to unplug the usb cable then swap the card and connect the usb cable
> again.  In the end I went and bought a different card reader, which does
> work correctly.

Well, this one is internal reader, which plugs into a 3" slot.
AND it also has the regular floppy drive in it, too. It's a combo,
a floppy drive AND a USB flash reader.  As such, I can't easily
re-plug it (which definitely helps, too, but for that to work I
have to open the case), and I can't replace it either, because
this device is almost unique: I still need a floppy and there's
no other such combo drives, at least I wasn't able to find it.
It's a great device if you think of it: it connects two epochs
together...

> I highly suspect it is a mistake in the hardware causing the problem
> given the vast majority of readers do work correctly already.

So at least a) I'm not alone, and b) there's SOMETHING that works.
Excellent!

> So far I have had no problems with a silverstone, mitsumi, dell (in
> monitor), sandisk.  I have had a problem with a no name cheap "15 in
> 1" reader which I stopped using because plugging and unplugging got
> annoying.
> 
> So my recommendation is get a non broken device.

The thing is that with some older kernel(s) it defeinitely worked.
So I'd say it's the kernel which broke/regressed, not the hardware.
Suggesting to fix the hardware because new kernel does not work with
it anymore is.. strange at least.

And yes it was definitely a el cheapo no-name thing.  But a..
great (epochs!) and hence unique thing, see above.. ;)

I'll try to find out when it broke.  My first suspect was the patch
introduced not-so-recently (in 2.6.2x series) to support media
change notifications done by some hardware (wait for notify instead
of constantly polling).

Thanks!

/mjt
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