feat: raspberry pi U-Boot + GPT + btrfs boot chain

Switch Raspberry Pi builds from proprietary firmware direct-boot to a
firmware → U-Boot → GRUB → kernel chain using GPT partitioning:

- GPT partition layout with fixed UUIDs matching os_install: firmware
  (128MB), ESP (100MB), boot (2GB FAT32), root (btrfs)
- U-Boot as the kernel in config.txt, chainloading GRUB EFI
- Pi-specific GRUB config overrides (console, USB quirks, cgroup)
- Btrfs root with shrink-to-minimum for image compression
- init_resize.sh updated for GPT (sgdisk -e) and btrfs resize
- Removed os-partitions from config.yaml (now derived from fstab)

build/image-recipe/raspberrypi/img/etc/fstab

@@ -1,2 +1,4 @@
-/dev/mmcblk0p1  /boot   vfat    umask=0077  0   2
-/dev/mmcblk0p2  /       ext4    defaults    0   1
+PARTUUID=cb15ae4d-0001-4000-8000-000000000001  /boot/firmware  vfat    umask=0077  0   2
+PARTUUID=cb15ae4d-0002-4000-8000-000000000002  /boot/efi       vfat    umask=0077  0   1
+PARTUUID=cb15ae4d-0003-4000-8000-000000000003  /boot           vfat    umask=0077  0   2
+PARTUUID=cb15ae4d-0004-4000-8000-000000000004  /               btrfs   defaults    0   1

build/image-recipe/raspberrypi/img/usr/lib/startos/scripts/init_resize.sh

@@ -12,15 +12,16 @@ get_variables () {
   BOOT_DEV_NAME=$(echo /sys/block/*/"${BOOT_PART_NAME}" | cut -d "/" -f 4)
   BOOT_PART_NUM=$(cat "/sys/block/${BOOT_DEV_NAME}/${BOOT_PART_NAME}/partition")
 
-  OLD_DISKID=$(fdisk -l "$ROOT_DEV" | sed -n 's/Disk identifier: 0x\([^ ]*\)/\1/p')
-
   ROOT_DEV_SIZE=$(cat "/sys/block/${ROOT_DEV_NAME}/size")
-  if [ "$ROOT_DEV_SIZE" -le 67108864 ]; then
-      TARGET_END=$((ROOT_DEV_SIZE - 1))
+  # GPT backup header/entries occupy last 33 sectors
+  USABLE_END=$((ROOT_DEV_SIZE - 34))
+
+  if [ "$USABLE_END" -le 67108864 ]; then
+      TARGET_END=$USABLE_END
   else
       TARGET_END=$((33554432 - 1))
       DATA_PART_START=33554432
-      DATA_PART_END=$((ROOT_DEV_SIZE - 1))
+      DATA_PART_END=$USABLE_END
   fi
 
   PARTITION_TABLE=$(parted -m "$ROOT_DEV" unit s print | tr -d 's')
@@ -61,33 +62,24 @@ main () {
     return 1
   fi
 
-#   if [ "$ROOT_PART_END" -eq "$TARGET_END" ]; then
-#     reboot_pi
-#   fi
-
   if ! echo Yes | parted -m --align=optimal "$ROOT_DEV" ---pretend-input-tty u s resizepart "$ROOT_PART_NUM" "$TARGET_END" ; then
     FAIL_REASON="Root partition resize failed"
     return 1
   fi
 
   if [ -n "$DATA_PART_START" ]; then
-    if ! parted -ms --align=optimal "$ROOT_DEV" u s mkpart primary "$DATA_PART_START" "$DATA_PART_END"; then
+    if ! parted -ms --align=optimal "$ROOT_DEV" u s mkpart data "$DATA_PART_START" "$DATA_PART_END"; then
       FAIL_REASON="Data partition creation failed"
       return 1
     fi
   fi
 
-  (
-    echo x
-    echo i
-    echo "0xcb15ae4d"
-    echo r
-    echo w
-  ) | fdisk $ROOT_DEV
+  # Fix GPT backup header to reflect new partition layout
+  sgdisk -e "$ROOT_DEV" 2>/dev/null || true
 
   mount / -o remount,rw
 
-  resize2fs $ROOT_PART_DEV
+  btrfs filesystem resize max /media/startos/root
 
   if ! systemd-machine-id-setup --root=/media/startos/config/overlay/; then
     FAIL_REASON="systemd-machine-id-setup failed"
@@ -111,7 +103,7 @@ mount / -o remount,ro
 beep
 
 if main; then
-  sed -i 's| init=/usr/lib/startos/scripts/init_resize\.sh||' /boot/cmdline.txt
+  sed -i 's| init=/usr/lib/startos/scripts/init_resize\.sh||' /boot/grub/grub.cfg
   echo "Resized root filesystem. Rebooting in 5 seconds..."
   sleep 5
 else

build/image-recipe/raspberrypi/squashfs/boot/cmdline.txt

@@ -1 +0,0 @@
-usb-storage.quirks=152d:0562:u,14cd:121c:u,0781:cfcb:u console=serial0,115200 console=tty1 root=PARTUUID=cb15ae4d-02 rootfstype=ext4 fsck.repair=yes rootwait cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory boot=startos

build/image-recipe/raspberrypi/squashfs/boot/config.sh

@@ -27,20 +27,18 @@ disable_overscan=1
 # (e.g. for USB device mode) or if USB support is not required.
 otg_mode=1
 
-[all]
-
 [pi4]
 # Run as fast as firmware / board allows
 arm_boost=1
-kernel=vmlinuz-${KERNEL_VERSION}-rpi-v8
-initramfs initrd.img-${KERNEL_VERSION}-rpi-v8 followkernel
-
-[pi5]
-kernel=vmlinuz-${KERNEL_VERSION}-rpi-2712
-initramfs initrd.img-${KERNEL_VERSION}-rpi-2712 followkernel
 
 [all]
 gpu_mem=16
 dtoverlay=pwm-2chan,disable-bt
 
-EOF
+# Enable UART for U-Boot and serial console
+enable_uart=1
+
+# Load U-Boot as the bootloader (GRUB is chainloaded from U-Boot)
+kernel=u-boot.bin
+
+EOF

build/image-recipe/raspberrypi/squashfs/boot/config.txt

@@ -84,4 +84,8 @@ arm_boost=1
 gpu_mem=16
 dtoverlay=pwm-2chan,disable-bt
 
-auto_initramfs=1
+# Enable UART for U-Boot and serial console
+enable_uart=1
+
+# Load U-Boot as the bootloader (GRUB is chainloaded from U-Boot)
+kernel=u-boot.bin

build/image-recipe/raspberrypi/squashfs/etc/default/grub.d/raspberrypi.cfg

@@ -0,0 +1,4 @@
+# Raspberry Pi-specific GRUB overrides
+# Overrides GRUB_CMDLINE_LINUX from /etc/default/grub with Pi-specific
+# console devices and hardware quirks.
+GRUB_CMDLINE_LINUX="boot=startos console=serial0,115200 console=tty1 usb-storage.quirks=152d:0562:u,14cd:121c:u,0781:cfcb:u cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory"

build/image-recipe/raspberrypi/squashfs/etc/startos/config.yaml

@@ -1,6 +1,3 @@
-os-partitions:
-  boot: /dev/mmcblk0p1
-  root: /dev/mmcblk0p2
 ethernet-interface: end0
 wifi-interface: wlan0
 disable-encryption: true