#3145 PR merged: Support saving and restoring hybrid BIOS/UEFI bootloader setup and clean up bootloader detection

Labels: enhancement, bug, cleanup, fixed / solved / done

pcahyna opened issue at 2024-02-06 18:06:

Pull Request Details:

  • Type: Bug Fix / Enhancement

  • Impact: High

  • Reference to related issue (URL): also helps with the problem in #3128

  • How was this pull request tested?
    Full backup and recovery on a hybrid UEFI/BIOS bootloader setup, with UEFI firmware.

  • Description of the changes in this pull request:

    • Fixes a bug where a system with hybrid BIOS/UEFI boot was restored without the BIOS bootloader (GRUB2) and on subsequent mkrescue it will abort because it can't detect the bootloader - the BIOS bootloader was not found in the boot sector and the presence of the BIOS boot partition confused the EFI bootloader detection. In detail:
    • Support BOOTLOADER=GRUB/GRUB2 with UEFI. This will happen with hybrid boot: BOOTLOADER=GRUB2 indicates that there is the BIOS version of GRUB2 installed and at the same time, USING_UEFI_BOOTLOADER=1 indicates theat there is also an EFI bootloader. Note that it is now perfectly legal to have USING_UEFI_BOOTLOADER=1 and BOOTLOADER neither EFI nor GRUB2-EFI nor ELILO. This will happen with hybrid BIOS/UEFI booting: BOOTLOADER will be detected as GRUB2, but USING_UEFI_BOOTLOADER=1.
    • Detect GRUB2 earlier - when saving layout. We used to distinguish between GRUB and GRUB2 when reinstalling the bootloader. This meant that the saved bootloader was wrong: GRUB for GRUB2. Detect GRUB2 earlier, already at the moment when we guess the bootloader, and save the correct value. This should help with the problem reported in PR #3128 (misdetection of GRUB2 as GRUB on any non-SUSE distro).
    • Don't look for EFI bootloader in the start of disk. EFI bootloader is not installed to the start of the disk, but to the EFI System partition as a regular file. It is this futile to search for EFI bootloaders in the first sectors of disks. If we find "EFI", it is only because there is a GPT, and "EFI PART" is the GPT signature (this does not tell anything about the presence of an EFI bootloader). See https://github.com/rear/rear/commit/67ac463446a5b140ea1eb1d9268e86422f869ebf#r138332329 .
    • Delete the code that checked for 'Hah!IdontNeedEFI' as a special case - it is not needed now. The code effectively skipped the check for EFI when there was a BIOS boot partition. Its presence does not indicate the absence of an EFI bootloader, though. We could be on an UEFI machine with the disk partitioned in hybrid (BIOS/UEFI compatible) mode. In this case ReaR can error out if legacy GRUB is not installed, because it does not find any bootloader (the EFI check is skipped).

pcahyna commented at 2024-02-08 15:52:

@rear/contributors I plan to merge it tomorrow unless there are objections.

[Export of Github issue for rear/rear.]