0153-uefi-only: init

rfcs/0153-uefi-only.md

@@ -0,0 +1,93 @@
+---
+feature: uefi_boot_only
+start-date: 2023-06-16
+author: Ryan Lahfa
+co-authors: (find a buddy later to help out with the RFC)
+shepherd-team: (names, to be nominated and accepted by RFC steering committee)
+shepherd-leader: (name to be appointed by RFC steering committee)
+related-issues: (will contain links to implementation PRs)
+---
+
+# Summary
+[summary]: #summary
+
+NixOS should drop support for legacy boot and assumes that
+all systems can be booted off UEFI.
+For legacy boot systems, an UEFI-providing environment bootloader should be used to polyfill
+for UEFI features.
+
+# Motivation
+[motivation]: #motivation
+
+Legacy boot is defined by the BIOS Boot specification, written in 1996: https://www.scs.stanford.edu/nyu/04fa/lab/specsbbs101.pdf.
+Nowadays, computers are defaulting to UEFI more and more for the extended features provided (e.g. SecureBoot, native network boot, etc.).
+
+Nevertheless, many legacy boots machines or machines that does not have support for UEFI are used with NixOS: Single Board Computers for example
+on other architectures.
+
+In nixpkgs, legacy boot forces a dichotomy between `boot.loader.efi` and... two legacy bootloaders: GRUB and a family of UBoot/extlinux-compatible/etc.
+
+In the case of GRUB, there are increasing problems with this bootloader:
+
+- Upstream do not do releases anymore: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/tools/misc/grub/default.nix#L62-L350
+- Co-maintenance / release work with other ecosystems such as the kernel is simply not done: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/tools/misc/grub/default.nix#L345-L349 causing GRUB's drivers to explode in production for our users: https://github.com/NixOS/nixpkgs/pull/235222
+- Our own maintenance of GRUB is subpar: https://github.com/NixOS/nixpkgs/pull/227741 https://github.com/NixOS/nixpkgs/pull/226821 https://github.com/NixOS/nixpkgs/pull/195805 https://github.com/NixOS/nixpkgs/pull/95901 https://github.com/NixOS/nixpkgs/pull/236027
+- GRUB installation procedure uses `install-grub.pl`, one of the remaining Perl script: https://github.com/NixOS/nixpkgs/pull/95901#issuecomment-756702696 offered to rewrite it with sponsoring, but no one took the offer yet, it is also very complicated to integrate with it: https://github.com/nix-community/lanzaboote/pull/96
+- GRUB installation procedure for UEFI-only is still confusing because our scripts does not handle well UEFI-only (you have to pass `nodev` and this is not very well documented). See https://github.com/NixOS/nixpkgs/issues/222491
+
+The worse about this, is this is our **default** bootloader for our install images **because** of legacy boot.
+
+In the case of UBoot/extlinux-compatible/etc. : we should definitely keep it as it is used by other ecosystems.
+
+Getting rid of legacy boot opens up the way to get rid of GRUB as a default and enable all our users to benefit from UEFI-in-mind developed abstractions.
+
+BIOS also hold back all improvements in the boot story, considering we are not held back by this, is very interesting for NixOS.
+
+# Detailed design
+[design]: #detailed-design
+
+Legacy boot is booted via UBoot or any bootloader able to provide an UEFI environment.
+
+Then, we boot using any usual bootloader, e.g. systemd-boot.
+
+# Examples and Interactions
+[examples-and-interactions]: #examples-and-interactions
+
+Fedora is considering doing this: https://lists.fedoraproject.org/archives/list/[email protected]/thread/GOETDM5SWINBX5ZDV37SWMHIPRRUVVTT/.
+
+Asahi Linux is booting UEFI via UBoot without EFI variables and it has been great for them.
+
+People who want to boot off strange partitions at boot-time can exploit UEFI drivers capability to load any filesystem driver and
+open the EFI System Partition in ZFS if they really insist.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+- 2-stage boot for legacy BIOS systems is more than 1-stage boot
+- Increased internal complexity in the boot story of NixOS
+- Increased load and reliance on UBoot
+- The runtime service `SetVariable` will probably stay highly unstable for a while (variable storage)
+
+# Alternatives
+[alternatives]: #alternatives
+
+- Keeping legacy BIOS and hoping someday it will be a bit more maintained
+- Getting rid of legacy BIOS without other options
+
+Then, if we don't do this, we will continue to have users relying on bootloaders with shady maintenance stories and a skewed perception of what a bootloader can do (e.g. boot on a ZFS partition?).
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+- How to migrate existing installs without any GPT partition table?
+- How to migrate existing installs with a GPT partition table but without a supported EFI System Partition, e.g. LVM
+  - NTFS, XFS, exFAT, Amiga FFS/SFS, BFS, UFS, ZFS are handled via https://efi.akeo.ie/ which is an EFI driver that can be loaded
+  - Subquestion: how to load EFI drivers for unsupported EFI System Partition?
+- When to do it?
+- What to do about variable storage (Asahi Linux showed this is not that important for a start)?
+- Design architecture in nixpkgs?
+
+# Future work
+[future]: #future-work
+
+- Improved support for UEFI features on non-UEFI native systems