Bug 1737042

Description of problem:

On Fedora and RHEL systems, Grub2 UEFI modules live in /usr/lib/grub*/x86_64-efi, not /boot, unless grub2-install is executed, but executing this tool is not needed with UEFI at all.
Additionally, only UEFI modules should be looked for, so /boot cannot be
searched but only /boot/grub2/x86_64-efi (similarly /usr/lib/grub*/x86_64-efi), otherwise we could get some false positives on dual boot systems (UEFI + Legacy), since modules for Legacy will also match, which is wrong.

This is a backport request for PR #2199 (https://github.com/rear/rear/pull/2199)

This causes the following error when booting the ReaR ISO:

Unknown command 'configfile'.
error: ../../grub-core/kern/fs.c:120:unknown filesystem
Entering rescue mode...
grub rescue> _


Version-Release number of selected component (if applicable):

rear-2.4 (RHEL7 and RHEL8)


How reproducible:

Always with UEFI systems

Steps to Reproduce:
1. Install a UEFI system
2. Install and execute ReaR

  # yum -y install rear
  # rear -dD mkrescue

3. Check the ReaR log and search for "grub2-mkimage -v -O x86_64-efi"

  # grep "grub2-mkimage -v -O x86_64-efi" /var/log/rear/rear-*.log

Actual results:

++ grub2-mkimage -v -O x86_64-efi -c /tmp/rear.BUo5lpm4WBrgx8w/tmp/mnt/EFI/BOOT/embedded_grub.cfg -o /tmp/rear.BUo5lpm4WBrgx8w/tmp/mnt/EFI/BOOT/BOOTX64.efi -p /EFI/BOOT

--> no module listed

Expected results:

++ grub2-mkimage -v -O x86_64-efi -c /tmp/rear.RhzDyyF3zXrQsWs/tmp/mnt/EFI/BOOT/embedded_grub.cfg -o /tmp/rear.RhzDyyF3zXrQsWs/tmp/mnt/EFI/BOOT/BOOTX64.efi -p /EFI/BOOT part_gpt part_msdos fat ext2 normal chain boot configfile linux jfs iso9660 usb usbms usb_keyboard video udf ntfs all_video gzio efi_gop reboot search test echo btrfs

--> modules being built into the image

Additional info:

The root cause is that only /boot is searched for Grub2 modules (ReaR tries to embed modules which do not exist on RHEL, see PR#2001). /usr/lib/grub*/x86_64-efi should be searched instead, and *only* this path (not /usr/lib/grub* globally).