cpc/UEFI: set the right partition type for the rootfs

To make our disk images more discoverable, we should use the correct
partition type for the root filesystem. This aligns with the
Discoverable Disk Image (DDI) specification developed by the UAPI
group[1] and makes our images more self-describing, e.g. with fdisk,
before:

Device         Start     End Sectors  Size Type
/dev/nbd0p1  2324480 7339998 5015519  2.4G Linux filesystem
...

and now after:

Device         Start     End Sectors  Size Type
/dev/nbd0p1  2324480 7339998 5015519  2.4G Linux root (x86-64)
...

[1] https://uapi-group.org/specifications/specs/discoverable_partitions_specification/

live-build/functions

@@ -1404,3 +1404,43 @@ EOF
 EOF
     fi
 }
+
+# Determine the appropriate partition type UUID for the root filesystem
+# based on the architecture.
+# Please see https://uapi-group.org/specifications/specs/discoverable_partitions_specification/
+# for where the GUIDs come from.
+gpt_root_partition_uuid() {
+    local ARCH="$1"
+
+    if [ -z "${ARCH:-}" ]; then
+        echo "usage: gpt_root_partition_uuid <arch>"
+        exit 1
+    fi
+
+    case "${ARCH}" in
+        "amd64")
+            ROOTFS_PARTITION_TYPE="4f68bce3-e8cd-4db1-96e7-fbcaf984b709"
+            ;;
+        "arm64")
+            ROOTFS_PARTITION_TYPE="b921b045-1df0-41c3-af44-4c6f280d3fae"
+            ;;
+        "armhf")
+            ROOTFS_PARTITION_TYPE="69dad710-2ce4-4e3c-b16c-21a1d49abed3"
+            ;;
+        "riscv64")
+            ROOTFS_PARTITION_TYPE="72ec70a6-cf74-40e6-bd49-4bda08e8f224"
+            ;;
+        "ppc64el")
+            ROOTFS_PARTITION_TYPE="c31c45e6-3f39-412e-80fb-4809c4980599"
+            ;;
+        "s390x")
+            ROOTFS_PARTITION_TYPE="5eead9a9-fe09-4a1e-a1d7-520d00531306"
+            ;;
+        *)
+            echo "Unsupported architecture: ${ARCH}"
+            exit 1
+            ;;
+    esac
+
+    echo "${ROOTFS_PARTITION_TYPE}"
+}

live-build/ubuntu-cpc/hooks.d/base/disk-image-ppc64el.binary

@@ -24,7 +24,9 @@ create_partitions() {
     sgdisk "${disk_image}" \
         --new=2::+8M \
         --new=1:
-    sgdisk "${disk_image}" -t 2:4100
+    sgdisk "${disk_image}" \
+        -t 2:4100 \
+        -t 1:"$(gpt_root_partition_uuid $ARCH)"
     sgdisk "${disk_image}" \
         --print
 }

live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi.binary

@@ -41,7 +41,8 @@ create_partitions() {
                    --typecode=15:ef00 \
                    --new=13::1G \
                    --typecode=13:ea00 \
-                   --new=1:
+                   --new=1: \
+                   --typecode=1:"$(gpt_root_partition_uuid $ARCH)"
             ;;
         riscv64)
             sgdisk "${disk_image}" \
@@ -51,6 +52,7 @@ create_partitions() {
                    --new=15::+106M \
                    --typecode=15:ef00 \
                    --new=1:: \
+                   --typecode=1:"$(gpt_root_partition_uuid $ARCH)" \
                    --attributes=1:set:2
             ;;
         amd64)
@@ -62,7 +64,8 @@ create_partitions() {
                    --new=1::
             sgdisk "${disk_image}" \
                    -t 14:ef02 \
-                   -t 15:ef00
+                   -t 15:ef00 \
+                   -t 1:"$(gpt_root_partition_uuid $ARCH)"
             ;;
     esac
     sgdisk "${disk_image}" \