linux-kernel - Re: [PATCH] mmc: add module parameter to set whether cards are assumed removable

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Message-ID: <1259594866.13049.56.camel@maxim-laptop>
Date:	Mon, 30 Nov 2009 17:27:46 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Pierre Ossman <pierre@...man.eu>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Ben Hutchings <ben@...adent.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mmc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	504391@...s.debian.org,
	Wouter van Heyst <larstiq@...stiq.dyndns.org>
Subject: Re: [PATCH] mmc: add module parameter to set whether cards are
 assumed removable

On Mon, 2009-11-30 at 13:51 +0000, Alan Cox wrote: 
> > Before we do suspend, pick few random sectors from the media, run that
> > through some hash function, thus creating some sort of watermark.
> 
> Statistically speaking the chances are you'll catch zero sectors and
> lose. You'll also not detect the suspend, move to other box, use, put
> back error. That is one users make and we need to be at least vaguely
> robust against.
> 
> Hence you need the fs checking here.
> 
> Alan
I have to agree with you about that one.
An FS checking is really only solution.

Then I think such check can be added gradually to existing filesystems
(starting with fat), and allow these filesystems to persist across low
power states regardsless of CONFIG_$system_UNSAFE_RESUME

For fat, simple checksum of the 'fat' table will catch most attempts.
Also directory modification times can be compared, at least for root
directory.

Best regards,
Maxim Levitsky



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