Subject: Re: install/19204: NetBSD/i386 does not support extended partition for the disklabel
To: None <>
From: David Laight <>
List: netbsd-bugs
Date: 11/29/2002 20:11:17
> >Synopsis:       NetBSD/i386 does not support extended partition for the disklabel

This is largely a restriction caused by the PC architecture.
Even if the installer were able to find/allocate an 'extended
partition' it would not be bootable by any of the standard
boot methods.

The early parts of the boot process are particularly problematical.
Not least because the first level bootstrap code has to reside
in sector 0 of the disk (along with the partition table).
The netbsd mbr_bootsel code is limited to 450 bytes of code,
searching for entended partition info would (probably) take up
too much space.  It isn't clear that any other disk sectors
can be used for additional code, the best bet is the first
sector of the extended partition - but you would have to both
read it and validate the contents.

I don't think that LILO will help either (it reads code from
elsewhere on the disk so isn't restricted to 1 sector) but
I don't believe it will try to boot an extended partition.

OTOH making the latter parts of the netbsd boot process
and the kernel understand extended partitions would let you
access a non-bootable disk, or boot via (for example) a
boot floppy.

It might be possible to squeeze in something to boot from
extended partitions in a version of the boot code that
only supported LBA reads.

(writing code for the initial boot isn't for the faint hearted,
gas doesn't support the correct instruction set!)


David Laight: