Text 2774, 77 rader
Skriven 2011-02-12 23:15:02 av Alex Taylor
Ärende: Re: advice on hardware purchase
=======================================
comp.os.os2.misc:2899 comp.os.linux.setup:7761
From: "Alex Taylor" <mail.me@reply.to.address>

On Sat, 12 Feb 2011 14:48:06 UTC, Jonathan de Boyne Pollard 
<J.deBoynePollard-newsgroups@NTLWorld.COM> wrote:

> >>> This may be related: http://bugs.ecomstation.nl/view.php?id=2914
> >>>
> >> Seems that I can't view the bug without an eCS userid.
> >>
> > You don't have one? Well, most of the same info is available in the 
> > same user's Ubuntu bug report:
> > https://bugs.launchpad.net/ubuntu/+bug/669459
> >
> > He also observes that it writes into the Windows partition as well...
> >
> 
> I've identified two things being adjusted.
> 
> The secondary MBR in relative block #0 of an extended partition is being 
> modified.  The modifications are essentially twofold.  The IBM 
> extensions to the partition table, containing the 8-character partition 
> name and "bootable" flag, are being zeroed out wholesale.  And the start 
> block numbers of the contained partition entries are being reduced by 61 
> (0x3D), reducing the first, for example, from 63 to 2.  The added 
> information in block #1 that we can see from the diff is actually the 
> LVM information, moved from block #62 of the container to block #1.
> 
> The primary MBR in absolute block #0 is being modified.  The 
> modifications are to the fourth entry in the partition table.  Its start 
> position is being increased by 0x3D and its length is being decreased by 
> 0x3D.  It's a fairly easy deduction that the fourth entry is the 
> extended (type 0x0F) container partition.

Thanks for this valuable analysis.  May I suggest that either you or
somebody with an account on their ticketing system might want to add
this information to the Ubuntu bug ticket?


> The idea that partitions have to be track aligned to the geometry 
> used at the INT 13h interface, whence this track's-worth of wasted 
> space comes from, has been a nonsense for almost two decades at this 
> point.  

Maybe it is, but there is demonstrably an existing base of legacy 
software that rigidly assumes it.  (OS/2 has always been notoriously 
strict about this, or at any rate since the Warp 3 days at least.)

According to Jan van Wijk, the relevant standards don't clearly define
what the correct behaviour in this case is, hence the trouble that
people have getting different OSes to cooperate (as each OS may well
take a different interpretation of what constitutes acceptable 
behaviour).

Personally -- not knowing much about low-level disk layout but from
a more generic perspective as a software engineer -- OS/2 may be guilty
of overly pedantic behaviour, but Ubuntu is also being grossly 
presumptuous.  Software should err on the side of conservatism when
manipulating critical data like disk geometry, especially when it needs
to be shared with other software (OSes) that don't necessarily share
one's own way of doing things.


> You'll probably want to direct M. Kluge to this diagnosis.

I'll see if I can put this into the eCS ticket, although somebody else
will have to do that for the Ubuntu ticket...

-- 
Alex Taylor
Fukushima, Japan
http://www.socis.ca/~ataylo00

Please take off hat when replying.

--- Internet Rex 2.31
 * Origin: Newscene Usenet News Service, http://www.newscene.co (1:261/20.999)