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

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Date:	Mon, 30 Nov 2009 14:09:28 +0100
From:	Pierre Ossman <pierre@...man.eu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	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, 30 Nov 2009 12:54:05 +0000
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> 
> 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.
> 
> 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.
> 

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.
> 
> 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.
> 
> 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.
> 

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
-- 
     -- Pierre Ossman

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