limited uuid options for ubuntu-boot when using gpt part table

[Ondrej Kubik]

If gpt part schema is used, there is limited list of permitted UUIDs which can be used for ubuntu-* partitions.
At the moment UUIDs for swap and ext4 are only supported.
Ideally we should be able to choose also C12A7328-F81F-11D2-BA4B-00A0C93EC93B
for vfat, which might be preferred fs with u-boot bootloader.

Device with following gadget.yaml fails to boot as snapd refuses to recreated ubuntu-boot partition with vfat

device-tree-origin: kernel
volumes:
  emmc:
    schema: gpt
    bootloader: u-boot
    structure:
      - name: ubuntu-seed
        role: system-seed
        filesystem: ext4
        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
        size: 500M
      - name: ubuntu-boot
        role: system-boot
        filesystem: vfat
        type: C12A7328-F81F-11D2-BA4B-00A0C93EC93B
        size: 200M
        content:
          - source: boot.sel
            target: uboot/ubuntu/boot.sel
      - name: ubuntu-save
        role: system-save
        filesystem: ext4
        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
        size: 16M
      - name: ubuntu-data
        role: system-data
        filesystem: ext4
        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
        size: 2GB

[Samuele Pedroni (pedronis)]

I don't see why we would use the EFI System Partion GUID with u-boot?

What we can allow is EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 , which is windows basic data partition I suppose.

[Ian Johnson (anonymouse67)]

I don't think we need to use C12A7328-F81F-11D2-BA4B-00A0C93EC93B with u-boot, since the partition being created is not an EFI system partition, for reference the pc gadget has this for ubuntu-seed because while ubuntu-seed is vfat, it is also the EFI system partition that gets booted off, i.e. ubuntu-seed has grub and shim and friends on it so it needs to be the EFI system partition type, but there is no such constraint on u-boot AFAICT unless somehow u-boot is being used with EFI somehow

[Ondrej Kubik (ondrak)]

Yes, Windows data partition is the one I'd expect to be allowed.
Agree no need for EFI type, as this is ubuntu-seed.

[Samuele Pedroni (pedronis)]

a fix for this was landed in https://github.com/snapcore/snapd/commit/a3666d47e58c6a2d52645f526e2d4f94753623a0 for 2.51