Simultaneous EFI and Legacy bootloader installation

[Lennart Sorensen]

On Tue, Mar 29, 2016 at 07:50:27PM -0500, Mario_Limonciello at Dell.com wrote:
> Hi,
> 
> I was briefly discussing this with Steve McIntyre and wanted to bring it to a wider discussion.  Currently users need to make a selection at installation time whether to install in UEFI mode or in Legacy mode.  If they installed in legacy mode and later discovered that their system supported extra features in UEFI mode (For example firmware updates) they are penalized and need to redo the installation in order to switch modes.
> 
> I'd like to propose changing this and by default install both legacy and UEFI bootloaders on architectures that support both regardless of which mode the system is running in at installation. Making this change has a few obvious implications:
> * The installation disk would always be formatted GPT.
> * An ESP would always be created.
> * If the user is in legacy at installation time, it's not possible to create an EFI boot entry since EFI runtime services aren't present.  The removable media fallback path (\efi\boot\boot$ARCH.efi) will need to be used to boot the system at this point and at some point create a "debian" NVRAM boot entry
> 
> I'm not aware of any modern systems that are unable to boot a GPT partitioned disk.  If there are systems like this in the wild, it would be worthwhile to leave support to install in MBR mode when doing an expert install so that people can still use them.

Certainly windows can NOT boot GPT disks if booted in legacy mode,
and can only boot GPT disks in UEFI mode.

So you sure can't choose GPT always if there is any other OS ever going
on the machine because it won't be able to boot in legacy mode.

It is possible with grub to mix things although it isn't usually done.
Booting legacy mode from a GPT disk requires an extra BIOS Boot partition
to be created to install grub while booting in UEFI mode requires that
there be a system partition for the boot loader.  So quite different.

Both could in theory coexist, although you have to have booted in UEFI
mode to update the NVRAM settings to even add Debian (or anything else)
to the UEFI boot settings, so it can't be done while in legacy mode.

So sure GPT is nice and all as a default if you only ever want to install
Linux (and Linux that knows how to boot legacy mode on GPT) and never
anything else.  Is that really a nice default to force on users?  I would
think it isn't.

-- 
Len Sorensn