Re: gpt booting status?

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

On Tue, Dec 30, 2014 at 07:13:15PM +0000, David Laight wrote:
> On Wed, Dec 24, 2014 at 09:30:31PM -0500, Greg Troxel wrote:
> > 
> > and a further question:
> > 
> >   I know /boot (with MBR) can skip the raidframe header.  So given a
> >   disk with a single MBR partition of type RAID, and an inside-the-RAID1
> >   disklabel with raid0a starting at 0, booting works.  (I'm sure because
> >   I do this all the time.)
> > 
> >   But, if I have gpt, with a RAID partition, and in the RAID1 have
> >   another gpt label, and in that a partition, is there any way to boot
> >   from that?  Basicallly I'm thinking
> > 
> >     sd0
> >       A=gpt partition 1, type raid, starts at 1024, big
> >         raid0  (so starts at 1024*64)
> >           B=gpt partition 1, starts at say 1024+64+64
> > 
> >    and would like the bootxx_ffsv2 code written to the beginning of
> >    A to see type 'raid', skip 64, and then interpret gpt vs mbr and find
> >    the active inner gpt partition.
> 
> The code that reads /boot (last time I looked) doesn't inspect any inner
> labels (of any type). It just had a nasty hack to look for a filesytem
> a further 64 sectors down the disk if it doesn't find /boot in the
> expected place.
> 
> Maybe a gpt disk has space for a larger boot image?
> In which case it might be possible to have more code to find /boot.

Not when booted by PC-BIOS.  All the GPT MBR does is locate load and run
a bootable GPT partition.  This partition still contains the bootxx code
just like any other bootable partition on x86.

	Jonathan Kollasch