Re: [RFT] nested partition issues

[Grégoire Sutre]

Hi,

The main issue at hand is that, to support NetBSD, we need a working
grub-setup for the (very common) case where the NetBSD disklabel is placed
in an MSDOS partition.

If we need to add yet other ``strcmp (..._partmap->name, ...)'' tests to
grub-setup, then we likely have bad abstractions.


> Actually now we follow the actual nesting of partitions. Even though
> net-/openbsd label metadate is placed inside a partition it still
> describes the whole disk as is manifested by it having entries for
> partitions not contained inside the partition containing label metadata.
> E.g.
> (hd0,netbsd6) may be physically contained within (hd0,msdos3) but still
> be described inside the label present in second sector (hd0,msdos2).
> Place of metadata is secondary to deciding what the nesting of
> partitions is. Primary criteria is what this metadata describes.

So, basically, as soon as a disklabel uses absolute offsets, this disklabel
must be viewed as a top-level disklabel?

I'm afraid that this will make things more complicated than they should
be.  But that's just me.


> This is, of course, very unfortunate design but since we support NetBSD
> we need such hacks. It's better than being faced with the problems of
> kind "My XYZOS handles my partition scheme perfectly but GRUB doesn't
> see half of partitions."

I did not see reports of such problems (for NetBSD partitions) since I
merged the code to ``external'' partitions [1].  Could you please point me
to such reports?

In the previous implementation, if partition e: in a NetBSD disklabel is
discarded, it's because e: describes an ``external'' partition.  This
external partition is (in all useful cases) described in another partition
map, where it is properly nested, hence it will be found by GRUB.

Grégoire

[1] http://lists.gnu.org/archive/html/grub-devel/2010-07/msg00109.html