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On Sep 23, 2004, at 10:15 AM, Bill Studenmund wrote:

> Oh, I thought wedges had a starting offset which was relative to the
> underlying device.

Wedge offsets are relative to their parent, which in this case is the 
underlying disk device (since I have explicitly chosen to disallow 
wedges-on-wedges, for now).

The problem I am getting at is... take a look at a BSD disklabel on a 
PC, where that disk also has an MBR, possibly shared with another OS 
(e.g. Windows):

#        size    offset     fstype [fsize bsize cpg/sgs]
  a: 294250496  16386300     4.2BSD   4096 32768    64  # (Cyl.   1020 - 
  19336*)
  b:   2098948 310636796       swap                     # (Cyl.  19336*- 
  19466*)
  c: 296349444  16386300     unused      0     0        # (Cyl.   1020 - 
  19466*)
  d: 312735744         0     unused      0     0        # (Cyl.      0 - 
  19466*)
  e:  16386237        63       NTFS                     # (Cyl.      0*- 
   1019)

This disklabel resides inside an MBR, but the partition offsets in the 
disklabel are not relative to the MBR partition, they're absolute (i.e. 
"relative to the beginning of the disk").  This is the problem with a 
generalized wedge nesting approach, in which the label inside a wedge 
would be presumed to have offsets relative to the wedge.

I forget ... do MBR Extended Partitions specify absolute offsets, or 
offsets relative to the chunk that contains the nested MBR partition 
map?

         -- Jason R. Thorpe <thorpej@shagadelic.org>


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