linux-kernel - Re: Extended partition mapping wrong size

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Date:	Tue, 6 Apr 2010 09:58:39 -0400
From:	Phillip Susi <psusi@....rr.com>
To:	Karel Zak <kzak@...hat.com>
CC:	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Extended partition mapping wrong size

On 4/6/2010 7:47 AM, Karel Zak wrote:
> This is probably kernel bug. It's really insane that the extended
> pseudo partition overflows to the next logical partition.

Indeed.

>  Please no. I think the size should not be more than 2 sectors (1024
>  bytes). The current concept works for years and we have in userspace 
>  /etc/partitions parsers that use "if (blocks <= 1)" to detect
>  extended partitions.

Could you elaborate a bit on this?  What programs have such tests and
what would they do differently if it were larger?

>  The other problem are mkfs programs, the space used for alignment
>  could be 1MiB (or more) -- it's enough many mkfs programs.

What's wrong with that?  If you REALLY want to, there's no reason you
can't create a tiny fs there.  Then again, I could swear that once upon
a time the kernel simply did not bother creating a dev node for the
extended partition, and this seems to be a hack that was put in to make
it easy for LILO to install to one.  Personally I'd prefer going back to
the old behavior of just not having a useless device there.

>  BTW, Linux does not use this policy for the others nested partition
>  tables (e.g. Solaris, BSD, Minix, ...). The extended dos partition
>  table is exception. The primary partitions for the others nested PT
>  are exported to the system with its real size :-)

Indeed, also the hidden space in the logical partitions is also not
exposed, otherwise you would have two dev nodes per logical partition.
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