using GPT support in BIOS boot

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

Hi,

Just a quick summary of how to use the new GPT support in the x86
boot stack.  (sysinst doesn't understand this yet.)

# gpt create wd1
# gpt add -b 64 -s 2097152 wd1
# dkctl wd1 addwedge wd1_1 64 2097152 ffs
# newfs -O2 dk0
# installboot /dev/rdk0 /usr/mdec/bootxx_ffsv2
# gpt biosboot dk0
# mount /dev/dk0 /mnt
# cp -p /usr/mdec/boot /mnt/

That's the basics, you'll want a kernel and root file system
on dk0 too to completely test this out.

Features:
- You can boot from a root partition at or above 2TiB if your BIOS
  properly supports block addresses above the 32-bit barrier.

Limitations:
- The GPT MBR only supports 128 partitions (the default and minimum).
- "/boot" only understands the first 26 partition entries (hdX[a-z]).

Thanks to Mike M. Volokhov for his work during GSoC 2009 that
made this possible.

        Jonathan Kollasch