Module efivars 
Source - EfiLoaderFeatures
 - Feature flags as described in https://systemd.io/BOOT_LOADER_INTERFACE/
 - EfiStubFeatures
 - Feature flags as described in https://www.freedesktop.org/software/systemd/man/systemd-stub.html
 
- BOOT_LOADER_VENDOR_UUID
 - systemd loader’s GUID
!= systemd’s GUID
https://github.com/systemd/systemd/blob/main/src/boot/efi/util.h#L114-L121
https://systemd.io/BOOT_LOADER_INTERFACE/
 
- cstr16_to_bytes
 - ensure_efi_variable
 - Ensures that an UEFI variable is set or set it with a fallback value
computed in a lazy way.
 - export_efi_variables
 - Exports systemd-stub style EFI variables
 - from_u16
 - get_loader_features
 - Get the currently supported EFI features from the loader if they do exist
https://systemd.io/BOOT_LOADER_INTERFACE/