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Re: [PATCH] nested partitions

From: Vladimir 'phcoder' Serbinenko
Subject: Re: [PATCH] nested partitions
Date: Mon, 3 Aug 2009 00:36:19 +0200

On Mon, Aug 3, 2009 at 12:17 AM, Robert Millan<address@hidden> wrote:
> On Fri, Jul 31, 2009 at 09:48:21PM +0200, Vladimir 'phcoder' Serbinenko wrote:
>> The proble it doesn't solve is when 2 partition labels pretend to
>> describe the same region. Solaris during install dd'es MBR to its
>> partition that it subdivides in further paritions. This way the
>> parition seems to have 2 valid subpartitioning tables. I think the
>> most sane way to handle this is to introduce partition labels
>> priority.
> Priority lists sound like an overkill solution.
I'm not sure that you see the problem. Let's say we have a disk
containing sun_pc label. sun_pc uses only sector number 1. So in
sector 0 you can put a standard msdos. So the same area is described
by 2 labels and grub has decide which to choose. If it was a purely
theoretical situation I wouldn't care. Unfortunately it's the
situation one encounters with opensolaris installer or if a bootsector
contains a lookalike of msdos partition (64 bytes zeros plus a
bootsector signature is a valid msdos label).
You can look at the patch if you want (I wasn't going to submit it yet
actually). It adds only 14 bytes to core size (first version added 6
but had a bug fixing which added another 8 bytes)
> In practice, how many
> times are we going to recurse at most?
In practise we probably won't have more than 2 levels of partitions.
But code for just 2 levels and for unlimited number of levels is of
the same complexity. So I prefer to avoid artitficial limit. But AFAIK
no OS is able to load from a 3-nested partition except perhaps using
tricks like loopbacks.
I'm aware of 4 situations when nested partitions are used
BSDlabel inside msdos for *BSD
sun_pc (patch ready but not submitted yet) inside msdos for OpenSolaris.
msdos inside msdos for minix
msdos inside GPT is described in GPT specification but I never saw it to be used
I vaguely heard of sun partitions inside apple partitions and AROS
mixing amiga and msdos

> --
> Robert Millan
>  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
>  how) you may access your data; but nobody's threatening your freedom: we
>  still allow you to remove your data and not access it at all."
> _______________________________________________
> Grub-devel mailing list
> address@hidden

Vladimir 'phcoder' Serbinenko

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