Subject: Re: overlap, was Re: Work-in-progress "wedges" implementation
To: Bill Studenmund <email@example.com>
From: Jason Thorpe <firstname.lastname@example.org>
Date: 09/24/2004 17:30:31
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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
# size offset fstype [fsize bsize cpg/sgs]
a: 294250496 16386300 4.2BSD 4096 32768 64 # (Cyl. 1020 -
b: 2098948 310636796 swap # (Cyl. 19336*-
c: 296349444 16386300 unused 0 0 # (Cyl. 1020 -
d: 312735744 0 unused 0 0 # (Cyl. 0 -
e: 16386237 63 NTFS # (Cyl. 0*-
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
-- Jason R. Thorpe <email@example.com>
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