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Date: Fri, 17 Sep 2010 12:44:39 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] CMOS file support
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To: Mathias Krause <mathias.krause@secunet.com>
Cc: qemu-devel@nongnu.org

Hi Mathias,

Am 17.09.2010 08:42, schrieb Mathias Krause:
>> Using QEMU's block devices instead of a simple file would be
>> more consistent with the rest of QEMU and allow reading the
>> CMOS data not only from a file but also from an URL or other
>> sources.
> 
> Thanks for the hint. Since this is my first contribution to the project
> I'm not that familiar with the code. Looking at other places, e.g. how
> the -kernel option gets handled, I just see FILE everywhere. Can you
> give me some pointers how to use this interface?

Have a look at block.h which contains the prototypes for the public
block layer interface.

Basically, you need to create a BlockDriverState with bdrv_new() and
then open it with bdrv_open(). You'll want to specify the raw block
driver for opening the image, you get it with bdrv_find_format("raw").
bdrv_pread/pwrite are the right functions to access the file with byte
granularity (other functions work on 512 byte sectors). bdrv_delete
frees the the BlockDriverState when you're done.

HTH,
Kevin