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Re: [Patch] Discard incorrect nested partitions (fixes #29956)

From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: [Patch] Discard incorrect nested partitions (fixes #29956)
Date: Mon, 31 May 2010 20:35:18 +0200
User-agent: Mozilla-Thunderbird (X11/20091109)

Grégoire Sutre wrote:
> Hi,
> Regarding the nested partition code, there is an implicit assumption
> that each partition should be contained in its parent, i.e. its sectors
>  should also be sectors of its parent.
> This ``physical nesting'' is checked in grub_disk_read, but it would
> be better to check it before that.
> The attached patch discards partitions that are invalid w.r.t. physical
> nesting.  This solves, in particular, a problem related to NetBSD (and
> OpenBSD) disklabels.
There are few ramifications of this patch. First of all some partitions
which are just barely outside of the host partition will lead to
something like "partition not found" errors in grub-probe. This message
should be more informative (the easiest way is to issue a warning in
grub-probe if partitions are discarded except some cases where it's
known not to affect the functionality like 'd' "subpartitions", probably
such a warning in grub proper would be too annoying though).
Then if you check partitions when iterating no need to recheck in
> With this patch, ``external'' partitions in a disklabel simply do not
> show up as BSD partitions.  For instance (see bug #29956 for an image):
> MBR Partition table:
> 0: NetBSD    start 32, size 1000
> 1: DOS       start 1040, size 1000
> NetBSD Disklabel (stored in MBR partition 0)
> 5 partitions:
> #        size    offset     fstype [fsize bsize cpg/sgs]
>  a:      1000        32     4.2BSD
>  c:      1000        32     unused
>  d:      2048         0     unused
>  e:      1000      1040      MSDOS
> The e: partition is external: it is not contained in MBR NetBSD
> partition.
> Without the patch, we get:
> $ grub-probe -m /dev/null -t drive -d /dev/rvnd0e
> (/dev/rvnd0d,1,5)   # this is (/dev/rvnd0d,msdos1,bsd5)
> $ grub-probe -m /dev/null -t fs -d /dev/rvnd0e
> grub-probe: error: unknown filesystem.
> With the patch, we get:
> niagara# grub-probe -m /dev/null -t drive -d /dev/rvnd0e
> (/dev/rvnd0d,2)   # this is (/dev/rvnd0d,msdos2)
> niagara# grub-probe -m /dev/null -t fs -d /dev/rvnd0e
> fat
> The patch still accepts sub-partitions that start at the same
> (absolute) offset as the parent.  For instance, in the above example,
> ls -l in grub gives both (hd1,msdos1) and (hd1,msdos1,bsd1).  Should
> we discard (hd0,msdos1,bsd1), i.e. require that sub-partitions start
> at a strictly positive relative offset?
No. SUN partitions comonly start at offset 0.
> Grégoire
> ------------------------------------------------------------------------
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Vladimir 'φ-coder/phcoder' Serbinenko

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