Re: Format option for chainloading GRUB from BOOTMGR

[Andrey Borzenkov]

В Mon, 5 Aug 2013 13:30:04 -0400
Alexei Podtelezhnikov <address@hidden> пишет:

> Hi all,
> 
> Thanks to ideas in [1], I managed to chainload GRUB2 core.img from Windows
> 7 BOOTMGR. Here is the three steps.
> 
> 1) Create core.img with **full** direct unmounted path to grub directory
> starting from partition, for example
> 
> grub2-mkimage --output=./core.img --format=i386-pc --prefix=*(hd0,1)*/grub2
> biosdisk part_msdos ext2
> 

More robust is to use embedded config to search for partition UUID.
Hard disk enumeration may change between reboots.

> 2) Concatenate lnxboot.img
> 
> cat /boot/grub2/i386-pc/lnxboot.img ./core.img > ./grub2.img
> 
> 3) Place ./grub2.img onto windows boot partition and configure BCD with
> bcdedit.exe under Windows to load the file as a BOOTSECTOR application.
> 
> It turns out that ./grun2.img can be larger than 512 bytes. BOOTMGR will
> load it just fine. Now, to be honest, the second step is just annoying. Do
> you have a format option for grub2-mkimage that would automatically include
> lnxboot.img? It would make the whole process so much smoother and more
> logical. Just a suggestion.
> 

Adding something like i386-pc-lnx is relatively trivial from technical
PoV. The main problem is that we need to keep boot code and /boot/grub
directory in think - i.e. both must be updated in one step. Does BCD
configuration need update after grub2.img gets updated?

> Thanks,
> Alexei
> 
> 
> [1]
> http://blog.mudy.info/2010/08/boot-grub2-stage2-directly-from-windows-bootmgr-with-grub4dos-stage1/