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Bug#344617: marked as forwarded (gets confused by "whole disk" entry in

Subject: Bug#344617: marked as forwarded gets confused by "whole disk" entry in some partitioning schemes
From: Debian Bug Tracking System
Date: Wed, 31 May 2006 06:03:56 -0700
Your message dated Wed, 31 May 2006 14:55:21 +0200
with message-id <[email protected]>
has caused the Debian Bug report #344617,
regarding gets confused by "whole disk" entry in some partitioning schemes
to be marked as having been forwarded to the upstream software
author(s) [email protected]

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--- Begin Message ---
Subject: Fwd: Re: userspace incorrectly detects RAID d-i
From: martin f krafft
Date: Wed, 31 May 2006 14:55:21 +0200
retitle 344617 gets confused by "whole disk" entry in some partitioning schemes
tags 344617 + upstream help

Neil, this is an interesting issue we should think about. More
information is here: http://bugs.debian.org/344617

----- Forwarded message from Elliott Mitchell <[email protected]> -----

The key point here is that most partitioning schemes include a "whole
disk" entry in their table (notably SunOS-style, FreeBSD-style and
IRIX-style). This is most often the 3rd entry/device C ("controller"
perhaps?). MSDOS-style aren't /supposed/ to have such entries, but
someone silly could try to make their MSDOS-style tables look like
everyone else's (dd to the rescue!).

If the outermost slice is RAIDed, then the userspace detection routinues
will incorrectly detect the presence of a RAID set on the whole disk
slice (since the signatures are at the end, and the end of the whole
disk slice will likely be at the same place as the end of the outermost
slice) and tell the kernel to load the whole disk slice as one RAID set.

If the RAID level on the outermost slice differs from the level on other
slices (either different level, or even no RAID at all). This WILL
result in data destruction.

There are two handy schemes I see to detect this situation. First,
make the userspace routines identify the slicing scheme, know which slice
is the overlap one and also be able to identify the RAID autorun type
(0xfd). Second, retrieve the slice data from the kernel
(/proc/partitions) and avoid slices which overlap other slices.

The first looks to be more "correct", but requires userspace to know
about all the schemes that are out there. The second is incorrect, but
fairly easy to implement and has the advantage of catching broken
tables. For my money, go with the second.

----- End forwarded message -----

 .''`.     martin f. krafft <[email protected]>
: :'  :    proud Debian developer and author: http://debiansystem.info
`. `'`
  `-  Debian - when you have better things to do than fixing a system
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 is largely an invention of balzac."
                                                        -- oscar wilde

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