Investigate use of discoverable partitions

[CullenSharp]

Since we've started using the gpt partitioning scheme, I've been wondering if we can use more of the UAPI discoverable partitions specification¹. I've had success with setting up swap partitions with it: systemd has machinery to automatically discover a swap partition and turn it on (swapon) during userspace init. This has worked for me.

The genimage.cfg that I'm using over on the c3-&-gps-remaster branch tags the root partition using the Linux root (ARM) type uuid. I haven't tested this out, but it should allow for automatic discovery of the root partition. Currently, I'm telling the kernel which blockdev the root partition is on in the bootloader configuration through a kernel command line parameter.

  partition rootfs {
    partition-type-uuid = "root-arm"
    partition-uuid = "00000000-0000-0000-0000-000000000000"
    image = "rootfs.ext4"
  }

Footnotes

1. https://uapi-group.org/specifications/specs/discoverable_partitions_specification/#suggested-mode-of-operation ↩

[CullenSharp]

This did not work: when I removed the root command line argument from the bootloader configuration, systemd failed to discover the root partition. This likely requires further investigation. I haven't spent much time considering the design and function of our initrd, which be required for a jumper-less boot process.

[CullenSharp]

The static part uuid might be problematic too.