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

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Message-ID: <20091122114234.GA28590@one.lan>
Date:	Sun, 22 Nov 2009 12:42:35 +0100
From:	Wouter van Heyst <larstiq@...stiq.dyndns.org>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mmc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	504391@...s.debian.org, Pierre Ossman <pierre@...man.eu>
Subject: Re: [PATCH] mmc: add module parameter to set whether cards are
	assumed removable

On Mon, Nov 16, 2009 at 10:31:49PM +0000, Ben Hutchings wrote:
> On Mon, 2009-11-16 at 12:23 -0800, Andrew Morton wrote:
> > On Wed, 11 Nov 2009 04:44:36 +0000
> > Ben Hutchings <ben@...adent.org.uk> wrote:
> > 
> > > Some people run general-purpose distribution kernels on netbooks with
> > > a card that is physically non-removable or logically non-removable
> > > (e.g. used for /home) and cannot be cleanly unmounted during suspend.
> > > Add a module parameter to set whether cards are assumed removable or
> > > non-removable, with the default set by CONFIG_MMC_UNSAFE_RESUME.
> > > 
> > 
> > The description really doesn't give me enough info to work out what's
> > happening here and why this is being proposed.  But it smells nasty.
> 
> In general, it is not possible to tell whether a card present in an MMC
> slot after resume is the same that was there before suspend.  So there
> are two possible behaviours, each of which will cause data loss in some
> cases:
> 
> CONFIG_MMC_UNSAFE_RESUME=n (default): Cards are assumed to be removed
> during suspend.  Any filesystem on them must be unmounted before
> suspend; otherwise, buffered writes will be lost.
> 
> CONFIG_MMC_UNSAFE_RESUME=y: Cards are assumed to remain present during
> suspend.  They must not be swapped during suspend; otherwise, buffered
> writes will be flushed to the wrong card.
> 
> Currently the choice is made at compile time and this allows that to be
> overridden at module load time.

I'm running 2.6.32-rc7 with this patch applied and CONFIG_MMC_UNSAFE_RESUME=y
That works as desired for my non-removable case. Is it desired that I
test if 'removable=1' will thrash my filesystem?

Wouter van Heyst
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