Loading pmOS_root / boot partitions by UUID

How it currently works:

• bootloader gets the initramfs file:
  • androids: initramfs is together with the kernel in boot.img
  • pinephone: u-boot fork has logic to find out whether it was booted from eMMC or not
  • pinephonepro: tow-boot loads grub, which then grabs the initramfs file from the boot partition
    • grub detects the boot partition by label (pmOS_boot)
      • problem: if pmOS is installed on eMMC and SD, it may boot the wrong one
• bootloader passes kernel command-line
• initramfs figures out the root partition
  • pinephone: partition is in root= kernel parameter
    • correctly selects the partition, even if pmOS is installed on both SD and eMMC
  • all others: first encrypted partition found or by partition label (pmOS_root)
    • problem if there's an encrypted SD card and it gets wrongly detected as root partition (#1485 (closed))
    • problem if pmOS is installed twice (eMMC and SD)

How it could be done:

• UEFI devices: generate a grub config
  • boot partition
    • put the UUID of the boot partition into the grub config
  • root partition
    • put the root partition as root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX parameter into the grub config?
    • or maybe store the root partition's UUID as file in the initramfs since this would also work with androids?
• androids: maybe store the root partition's UUID as file in the initramfs?
• adjust postmarketos-mkinitfs to load the root partition by UUID if specified on kernel command-line
• I think generating the grub config would fit into boot-deploy (this gets called by postmarketos-mkinitfs already, e.g. to dd the boot.img to the right partition for androids)
• pmbootstrap install and on-device installer: must call boot-deploy after the installation and ensure it writes the right UUIDs (possibly with env vars)

Thoughts?