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Date: Wed, 02 May 2012 16:27:56 +0200
From: Christian Borntraeger <borntraeger@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] geometry detection: use HDIO_GETGEO
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To: Alexander Graf <agraf@suse.de>, Stefan Weinhuber <wein@linux.vnet.ibm.com>
Cc: Heinz Graalfs <graalfs@linux.vnet.ibm.com>, qemu-devel <qemu-devel@nongnu.org>, Jens Freimann <jfrei@linux.vnet.ibm.com>, Cornelia Huck <cornelia.huck@de.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>, Einar Lueck <elelueck@de.ibm.com>

On 02/05/12 14:54, Alexander Graf wrote:
> On 05/02/2012 01:38 PM, Paolo Bonzini wrote:
>>> On 05/02/2012 01:26 PM, Paolo Bonzini wrote:
>>>>> and everyone should be happy :). I would really like to have as
>>>>> little #ifdef TARGET_S390 code in QEMU. And #ifdef __s390__ is
>>>>> even worse,
>>>>> as it means we won't be able to execise that code path on other
>>>>> architectures.
>>>> True, but how do you exercise that code path with DASD geometry
>>>> on !__s390__?
>>> If we make things a flag for the guessing code, it should work just
>>> as well with image files, right?
>> Only when they're not blank. :)  I was only thinking of #ifdef __s390__
>> for the call to HDIO_GETGEO.
> 
> Well, if guessing is a function
> 
>   guess_size(disk_size, block_size)
> 
> then we would be able to do the same on an image file. Christian, would that work?

I think that the geometry values can not always be guessed correctly based on
block_size and disk_size.

Stefan, can you clarify that?

If we cannot reliably guess the geometry based on blocksize and size, I still think
that we should use the host values, e.g. after checking that BIODASDINFO2 returns 
successfully.

Christian