Date: Mon, 30 Nov 2009 14:09:28 +0100
From: Pierre Ossman <pierre@ossman.eu>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>,
       Ben Hutchings <ben@decadent.org.uk>,
       Andrew Morton <akpm@linux-foundation.org>, linux-mmc@vger.kernel.org,
       LKML <linux-kernel@vger.kernel.org>, 504391@bugs.debian.org,
       Wouter van Heyst <larstiq@larstiq.dyndns.org>
Subject: Re: [PATCH] mmc: add module parameter to set whether cards are
 assumed removable
Message-ID: <20091130140928.29d847a4@mjolnir.ossman.eu>
In-Reply-To: <20091130125405.541a6a01@lxorguk.ukuu.org.uk>
References: <1257914676.2237.57.camel@localhost>
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	<1258410709.2792.9.camel@localhost>
	<4B02565C.1030406@s5r6.in-berlin.de>
	<20091130133949.794fef00@mjolnir.ossman.eu>
	<20091130125405.541a6a01@lxorguk.ukuu.org.uk>
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On Mon, 30 Nov 2009 12:54:05 +0000
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

>=20
> For most file systems it is sufficient to check the superblock related
> information. So we'd need an fs->ops->validate_media() or somesuch but it
> wouldn't be that horrific or need to do much I/O in most cases.
>=20
> You could defeat that by being really stupid, but the purpose of the
> check isn't a stupidity filter but to stop accidents happening in normal
> use.
>=20

Agreed. Something like that would more or less solve the issue. Someone
just needs to write the code for all (or most) filesystems.

> > Another way of putting it is that the kernel needs to umount/mount
> > around suspend in a way that's transparent to users of the filesystem.
>=20
> No. The kernel needs to push stuff to media on suspend (which is good
> manners anyway), and validate on resume. if the validate fails you mark
> the media as changed and the block layer will already see to it that
> everything gets aborted as it already does with a truely removable device.
>=20
> In fact if you did this by media serial numbers and idents you don't even
> need the fs hook, although it would certainly be safer that way.
>=20

The hardware driver layer can only check if it's the same device being
plugged in, not if someone has done something with it during suspend,
so I see no other way than solving this in the filesystem layer.

Rgds
--=20
     -- Pierre Ossman

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