GPT BIOS boot partition and installing to a partition

GPT BIOS boot partition and installing to a partition

[Dave Vasilevsky]

On my GPT-partitioned MacBook, I seem to have two options for booting
with grub-pc:

1. Install grub to the start of an existing partition. This coexists
well with the rEFIt boot menu, but requires blocklists to load
core.img.
2. Use a BIOS boot partition. This allows embedding core.img, but
installs to the MBR and makes rEFIt unhappy.

I had the idea that we could get the advantages of both: Install the
boot-image to an existing partition, but load core.img from a BIOS
boot partition. With some creative hex-editing I got this working
without much difficulty.

Is there a technical reason why grub doesn't support this setup? If I
were to write a patch allowing this, what behaviour would be
preferred: Should 'grub-setup (hdX,Y)' automatically use a BIOS boot
partition if one exists, or should a command-line flag be required?

Dave Vasilevsky

Re: GPT BIOS boot partition and installing to a partition

[Vladimir 'phcoder' Serbinenko]

Dave Vasilevsky wrote:
> On my GPT-partitioned MacBook, I seem to have two options for booting
> with grub-pc:
>
> 1. Install grub to the start of an existing partition. This coexists
> well with the rEFIt boot menu, but requires blocklists to load
> core.img.
> 2. Use a BIOS boot partition. This allows embedding core.img, but
> installs to the MBR and makes rEFIt unhappy.
>
>   
On EFI system try grub-efi.
> I had the idea that we could get the advantages of both: Install the
> boot-image to an existing partition, but load core.img from a BIOS
> boot partition. With some creative hex-editing I got this working
> without much difficulty.
>
> Is there a technical reason why grub doesn't support this setup? If I
> were to write a patch allowing this, what behaviour would be
> preferred: Should 'grub-setup (hdX,Y)' automatically use a BIOS boot
> partition if one exists, or should a command-line flag be required?
>
>   
It may be a good idea but the best way is to use first sector of BPB for
this. But the usability is limited. For EFI systems we have grub-efi and
for BIOS boot you still need a specially adapted MBR for it anyway
> Dave Vasilevsky
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>
>   


-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git 

Re: GPT BIOS boot partition and installing to a partition

[Dave Vasilevsky]

phcoder wrote:
> On EFI system try grub-efi.

I have indeed tried grub-efi, you can see the notes I left here:
https://help.ubuntu.com/community/MactelSupportTeam/EFI-Boot-Mactel#MacBook4,1
. Unfortunately inability to use both accelerated X and the console
makes me prefer grub-pc for the moment. I appreciate all the work
you've put into grub-efi though, it's great to see it improving.

> the best way is to use first sector of BPB for
> this. But the usability is limited.

I'm not sure I'm understanding, isn't the BPB just a few dozen bytes
in the boot sector? Some filesystems have a bit more room, but usually
not very much. The advantage of using the BIOS Boot Partition is that
you can embed the entire core.img, no?

> for BIOS boot you still need a specially adapted MBR for it anyway

Agreed that this is sub-optimal, but on my system it's the lesser of
evils for now.

Cheers,
Dave

Re: GPT BIOS boot partition and installing to a partition

[Vladimir 'phcoder' Serbinenko]

Dave Vasilevsky wrote:
> phcoder wrote:
>   
>> On EFI system try grub-efi.
>>     
>
> I have indeed tried grub-efi, you can see the notes I left here:
> https://help.ubuntu.com/community/MactelSupportTeam/EFI-Boot-Mactel#MacBook4,1
> . Unfortunately inability to use both accelerated X and the console
> makes me prefer grub-pc for the moment. I appreciate all the work
> you've put into grub-efi though, it's great to see it improving.
>
>   
Workaround for your problem is described here:
http://grub.enbug.org/TestingOnMacbook
For the long run linux has to be fixed.
>> the best way is to use first sector of BPB for
>> this. But the usability is limited.
>>     
>
> I'm not sure I'm understanding, isn't the BPB just a few dozen bytes
> in the boot sector? Some filesystems have a bit more room, but usually
> not very much. The advantage of using the BIOS Boot Partition is that
> you can embed the entire core.img, no?
>
>   
It was a typo. I meant BBP (BIOS Boot Partition)


-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git 

Re: GPT BIOS boot partition and installing to a partition

[Dave Vasilevsky]

phcoder wrote:
> Workaround for your problem is described here:
> http://grub.enbug.org/TestingOnMacbook

Are you talking about fix_video? When I tested, without fix_video I
could use the console, but X was slow. With fix_video, X was
accelerated, but the console was scrambled as soon as X started.

>>> the best way is to use first sector of [BIOS Boot Partition]

This only works if the BBP is in the MBR. In my configuration, there
are already 4 partitions in the MBR, with no room for the BBP. That's
why I want to embed the boot-image in another partition, and have it
pass control to the BBP.

Dave

Re: GPT BIOS boot partition and installing to a partition

[Vladimir 'phcoder' Serbinenko]

Dave Vasilevsky wrote:
> phcoder wrote:
>   
>> Workaround for your problem is described here:
>> http://grub.enbug.org/TestingOnMacbook
>>     
>
> Are you talking about fix_video? When I tested, without fix_video I
> could use the console, but X was slow. With fix_video, X was
> accelerated, but the console was scrambled as soon as X started.
>
>   
This is X bug then
>>>> the best way is to use first sector of [BIOS Boot Partition]
>>>>         
>
> This only works if the BBP is in the MBR. In my configuration, there
> are already 4 partitions in the MBR, with no room for the BBP. That's
> why I want to embed the boot-image in another partition, and have it
> pass control to the BBP.
>   
GRUB2 doesn't need BBP to be in pseudo-MBR to boot
> Dave
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>
>   


-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git 

Re: GPT BIOS boot partition and installing to a partition

[Michael Scherer]

Le samedi 31 octobre 2009 à 15:09 -0400, Dave Vasilevsky a écrit :
> phcoder wrote:
> > Workaround for your problem is described here:
> > http://grub.enbug.org/TestingOnMacbook
> 
> Are you talking about fix_video? When I tested, without fix_video I
> could use the console, but X was slow. With fix_video, X was
> accelerated, but the console was scrambled as soon as X started.

I have got it working with fix_video and with a working intel driver,
with accelerated 3d on a fedora 12 .

here is the grub entry :

menuentry "Fedora boot" {
    root=(hd0,2)
    fix_video
    loadbios /EFI/grub/vbios.bin /EFI/grub/int10.bin
    search -s -f /vmlinuz-2.6.31.5-96.fc12.i686.PAE
    linux /vmlinuz-2.6.31.5-96.fc12.i686.PAE ro
root=/dev/mapper/vg_akroma-lv_root nomodeset rhgb=0
    initrd /initramfs-2.6.31.5-96.fc12.i686.PAE.img
}

Even plymouth is working fine.

The xorg driver is the following :
xorg-x11-drv-intel-2.9.1-1.fc12.i686

-- 
Michael Scherer

Re: GPT BIOS boot partition and installing to a partition

[Robert Millan]

On Sat, Oct 31, 2009 at 02:29:45PM -0400, Dave Vasilevsky wrote:
> On my GPT-partitioned MacBook, I seem to have two options for booting
> with grub-pc:
> 
> 1. Install grub to the start of an existing partition. This coexists
> well with the rEFIt boot menu, but requires blocklists to load
> core.img.

Why?  Can't you fix rEFIt instead?

> 2. Use a BIOS boot partition. This allows embedding core.img, but
> installs to the MBR and makes rEFIt unhappy.

That will lead to trouble.  The BBP is a shared resource, like MBR.  If
installing GRUB to a partition made use of it, it could overwrite other
things, which users wouldn't appreciate.

Besides, the whole notion of "installing a bootloader to a partition" is
specific to DOS-style labels anyway, and used only for compatibility with
Microsoft.  There isn't any real benefit in trying to archieve the same
thing on GPT.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."