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Re: [RFC/PATCH 0/2] support for CMS-formatted disks on the s/390 archite

From: Stephen Powell
Subject: Re: [RFC/PATCH 0/2] support for CMS-formatted disks on the s/390 architecture
Date: Wed, 21 Apr 2010 17:41:26 -0400 (EDT)

On Wed, 21 Apr 2010 14:14:38 -0400 (EDT), Stephen Powell wrote:
> On Wed, 21 Apr 2010 13:01:23 -0400 (EDT), Jim Meyering wrote:
>> If there's not a specification, can you deduce what vtoc_end
>> must be for a 2048-byte block size by looking at what other tools do?
> Well, there's the kernel source code of course.  The problem will be finding 
> it.
> Ultimately, how the kernel determines where the partition starts (and 
> therefore
> where the metadata ends) is the final authority.
> drivers/s390/block/dasd* would be a good place to start looking.

Well, I finally found the unassailable definition of where the partition
starts in the kernel source code, thanks to "grep -r".  (An indispensable
tool by the way!)  Look at the Linux kernel source tree in fs/partitions/ibm.c,
searching for the character strings "CMS1" and "LNX1".  That's the
unchallengeable definition for where the implict partition starts.  The 
ends at the end of the disk, and the metadata occupies everything from
the beginning of the disk until the start of the partition.  You can take
that to the bank.  If it's wrong here, then it will have to stay wrong or all
data recorded on existing partitions will become unreadable if IBM changes it.

However, not being a C programmer, I'm not 100% sure exactly what it's saying.
That's where you guys come in.

I think I'm going to bow out now because I suspect my code will have to be
discarded anyway because some manager doesn't want to expose his
posterior to possible unfavorable scrutiny later on for no perceived benefit.
I tried to submit code to IBM once, and was denied because management wouldn't
sign off on it.  So I'm not optimistic.

You have all the information you need now.  Of course, I'll be happy to test it
for you.  That doesn't require copyright assignment.
  .''`.     Stephen Powell    
 : :'  :
 `. `'`

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