linux-kernel - Re: Offset into block file for mounting?

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Date:	Mon, 3 Jan 2011 15:25:25 +0100 (CET)
From:	Martin Nybo Andersen <tweek@...ek.dk>
To:	Tom Watson <tsw@...ana.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Offset into block file for mounting?

Hi Tom,

On Mon, 3 Jan 2011, Tom Watson wrote:

> Hi...
>
> I recently got a "floppy drive emulator" that uses an USB thumb drive to
> emulate floppy images to be used as a floppy drive.  In trying out the
> software (it is a bit cryptic), I found that this model stores the
> floppy images consecutively on said thumb drive (with some padding to
> make the drives on 1.5 Mbyte borders on the thumb drive.  When plugging
> in the thumb drive, the 'vfat' module just mounts the first image (as I
> expect).  What I would like to do is mount some of the other images that
> exist (I dumped out the raw thumb drive).  I believe that a simple way
> to do this is to add an offset to the vfat mount, so that the accesses
> begin at (as in my example) 0x180000 (and multiples thereof) from the
> start of the physical drive.
>
> Is there any way to add such an offset?
> Would it be useful in any other file systems?

mount diskimage /dir -t vfat -o loop,offset=xxx,sizelimit=yyy

mount will then forward the offset and sizelimit options to losetup which 
sets up a loop device before mounting.

Have a look at the man-pages for mount and losetup. :-)

Hope that helps.

> [...]
> -- 
> Tom Watson <tsw@...ana.com>
> I'm at home now

-- 
Martin
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