Bug#1078656: grub-pc: please use 'grub-install --disk-module=native /dev/sdX'

[Pascal Hambourg]

On 14/08/2024 at 03:59, Martin-Éric Racine wrote:
> 
> You're welcome to suggest a better recipe.

insmod chain
insmod boot # not sure it is useful
set root=usb0
chainloader +1

But once loaded, the MBR boot code needs to access the USB drive via 
BIOS disk services, and it won't work if the BIOS does not expose the 
USB drive.

> Actually, it turns out that even installing this isn't practical on
> anything else than media with a GTP partition. It won't fit into the
> start of a DOS partition, whereas GTP always leaves plenty of empty
> space at the start.

What are you talking about ? 'grub-install --disk-module=native 
/dev/sdX' ? Do you mean "GPT" instead of "GTP" ? Do you mean "DOS 
partition table" instead of "DOS partition" ?

By today standards (1-MiB alignment) there is as much unallocated space 
after a DOS partition table and a GPT partition table. Only very old 
partitioning tools used cylinder alignment with the first partition 
starting at sector 63, which leaves ~31 KiB for GRUB core image. A core 
image embedding native disk drivers may not fit there. Besides, GRUB can 
use the unallocated space after the partition table only on DOS, not on 
GPT. GPT must have a "BIOS boot" partition instead.