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Re: [PATCH] nested partitions

From: Vladimir 'phcoder' Serbinenko
Subject: Re: [PATCH] nested partitions
Date: Mon, 17 Aug 2009 16:34:41 +0200

On Mon, Aug 17, 2009 at 4:06 PM, Robert Millan<address@hidden> wrote:
> On Mon, Aug 17, 2009 at 03:00:52PM +0200, Vladimir 'phcoder' Serbinenko wrote:
>> Rediff and few fixes
> Please note that after what we discussed on IRC, we need to find a solution
> that wouldn't make boot time increase linearly with the number of filesystems
> or partmaps GRUB supports.
It probe time scales linearly no matter what we do. Fortunately with
disk cache few first sectors are read and checked for different
signatures which is fast. As for module autoload with search patch it
doesn't happen except in the failure to access requested device.
> I really think supporting every sort of combination is too extreme.  For
> example who would want an msdos/msdos chain?  OpenSolaris creates one, but
> it's a false positive.
minix does it and it's not a false positive.
> The overall idea *is* nice.  Some combinations (e.g. msdos/bsd) are cleaner
> this way, but supporting everything doesn't scale well.
AFAIK no partmap goes beyond first 16K for signature checking. Time
for signature checking can be neglected and 16K would be read for
filesystem probe too. Additionally e.g. (hd0,1) is probed for
subpartitions only if (hd0,1,X) is requested or we're scanning through
partitions. In last case we're likely to fsprobe partition anyway so
it doesn't create any overhead
> Perhaps we can explicitly list which combinations make sense?  So when an
> msdos label is found, its partitions are probed for bsd labels too, but not
> for msdos labels again, etc.
> --
> 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."
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Vladimir 'phcoder' Serbinenko

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