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Re: [Qemu-devel] [PATCH 1/3] Fix geometry sector calculation

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 1/3] Fix geometry sector calculation
Date: Wed, 02 May 2012 13:05:44 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120425 Thunderbird/12.0

Il 02/05/2012 12:50, Christian Borntraeger ha scritto:
> On 02/05/12 12:25, Paolo Bonzini wrote:
>> Il 02/05/2012 12:18, Christian Borntraeger ha scritto:
>>> Maybe that really points to the problem that we are trying to solve here.
>>> For a dasd device, there is usually a 4096 byte block size and on the host
>>> these 4096 arereported via getss and getpbsz. 
>>> The geometry reported by the device driver is usually 15 head and 12 sectors
>>> per track, but actually means 12 sectors of 4096 bytes size (a track ~ 48k).
>>> What I want to achieve is that the guest view is identical to the host view
>>> for cyls, heads, secs, and all block sizes.
>> I think what you want is _not_ to have the same view as the host.  What
>> you want is simply to have a default that is consistent with what is
>> common on actual s390 disks.
> Let me put it in another way:
> I want to have these values to match the _device_ that we are passing to the 
> guest
> because several tools and the partition detection code for a compatible disk 
> format
> (those that can be accessed by z/OS) needs those values to work properly.

Ah, you never pass part of a disk to a guest and part of the same disk
to another?

> IOW the geometry for dasd devices is not an artifical number, it has some 
> real meaning
> that has a influence on the data structures on the disk.

Yes, I understood this.


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