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

[Stephen Powell]

On Sat, 17 Apr 2010 11:01:10 -0400 (EDT), Adam Thornton wrote:
> 
> I think that CMS disks can have a different logical block size than the 
> underlying DASD, but I also suspect that case is vary rare.

Not on CKD DASD.  On CKD DASD, the CMS minidisk block size is the
physical blocksize.  On FBA DASD, the physical block size is always
512.  But my patches, as I wrote them, apply only to CKD DASD.
EDF CMS minidisks can have a block size of 512, 1024, 2048, and 4096.
That's it.  If someone wants to add support for CMS minidisks on
FBA DASD, that would be great too.  (CMS minidisks are the only
disk format supported by the s390 Linux kernel for FBA DASD;
so if there's no support for CMS minidisks on FBA DASD, there is
essentially no support for FBA DASD.)

> At any 
> rate, the logical block size is in the CMS volume label, and might need 
> to be scaled according to what the disk says to make parted happy.

Since parted was originally written for PCs, where the physical block
size is 512, its internal calculations most deal with 512-byte blocks.
My patches take that into account.
  
> DIAG250 cares about the CMS block size; directly talking to the disk 
> with CCWs doesn't.  I think.  It's been a while since I had to know this.

Unfortunately, parted doesn't work at all when the DIAG driver is
used on CKD DASD.  I wish it did, and if someone wants to write a
patch to fix that problem, I'd be grateful.  But my patches, as written,
do not address that problem.

> 
> Anyway, if the patch didn't break anything for existing users it's 
> definitely an improvement.

Agreed!

-- 
  .''`.     Stephen Powell    
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