refactor: change eMMC layout - 3G overlay + data partition for Docker

expand-overlay now splits eMMC into:
- p3 (3GB): overlay filesystem (system + configs)
- p4 (~54GB): ext4 data partition -> /mnt/data/docker

Docker data-root auto-configured to /mnt/data/docker on first boot.

package/diy/expand-overlay/Makefile

@@ -18,15 +18,17 @@ include $(INCLUDE_DIR)/package.mk
 define Package/expand-overlay
   SECTION:=utils
   CATEGORY:=Utilities
-  TITLE:=Auto-expand overlay partition on first boot
-  DEPENDS:=+sfdisk +e2fsprogs
+  TITLE:=eMMC partition layout: 3G overlay + data partition
+  DEPENDS:=+sfdisk +e2fsprogs +block-mount
   PKGARCH:=all
 endef
 
 define Package/expand-overlay/description
-  Auto-resize the NanoPi R6C eMMC overlay partition (mmcblk2p3)
-  to fill all remaining unallocated space on first boot.
-  Two-stage: uci-defaults resizes partition table, init.d resizes filesystem.
+  First-boot eMMC partition layout for NanoPi R6C:
+  - p3 (3GB): overlay filesystem (system/config)
+  - p4 (~54GB): data partition (mounted at /mnt/data, for Docker)
+  Stage 1 (uci-defaults): resizes p3 to 3GB, creates p4.
+  Stage 2 (init.d): resizes p3 fs, formats & mounts p4.
 endef
 
 define Build/Configure

package/diy/expand-overlay/files/expand-overlay.init

@@ -1,25 +1,59 @@
 #!/bin/sh /etc/rc.common
 # /etc/init.d/expand-overlay
-# Stage 2: Resize filesystem to match expanded partition.
+# Stage 2: Resize p3 filesystem, format & mount p4, configure Docker.
 # Runs at START=99, after overlay is mounted and most services started.
 
 START=99
 
 boot() {
 	local flag="/etc/resize2fs.done"
-	[ -f "$flag" ] && return 0
+	local p4flag="/etc/data-partition.done"
 
-	# Wait for stage1 to finish (uci-defaults running before us)
-	local i=0
-	while [ ! -f "/etc/expand-overlay.done" ] && [ $i -lt 30 ]; do
-		sleep 1
-		i=$((i + 1))
-	done
+	# ---- Stage 2a: Resize p3 filesystem ----
+	if [ ! -f "$flag" ]; then
+		# Wait for stage1 (uci-defaults) to finish
+		local i=0
+		while [ ! -f "/etc/expand-overlay.done" ] && [ $i -lt 30 ]; do
+			sleep 1
+			i=$((i + 1))
+		done
 
-	[ ! -f "/etc/expand-overlay.done" ] && return 0
+		if [ -f "/etc/expand-overlay.done" ]; then
+			resize2fs /dev/mmcblk2p3 2>/dev/null
+			touch "$flag"
+		fi
+	fi
+
+	# ---- Stage 2b: Format and mount p4 data partition ----
+	if [ ! -f "$p4flag" ]; then
+		# Check if p4 is marked with RESET (needs formatting)
+		if dd if=/dev/mmcblk2p4 bs=5 count=1 2>/dev/null | grep -qF "RESET"; then
+			# Format p4 as ext4
+			mkfs.ext4 -F -L data /dev/mmcblk2p4 2>/dev/null
+		fi
+
+		# Mount p4 to /mnt/data
+		mkdir -p /mnt/data
+		mount /dev/mmcblk2p4 /mnt/data 2>/dev/null
+
+		# Create Docker directory on data partition
+		mkdir -p /mnt/data/docker
+
+		# Point Docker to data partition
+		uci -q set dockerd.globals.data_root="/mnt/data/docker"
+		uci -q commit dockerd
+
+		# Add to fstab for auto-mount on future boots
+		if ! grep -q "mmcblk2p4" /etc/config/fstab 2>/dev/null; then
+			block detect > /dev/null 2>&1
+			# block detect creates entries, we update the last one
+			local idx=$(( $(uci show fstab | grep -c "fstab.@mount") - 1 ))
+			[ "$idx" -ge 0 ] && uci -q set fstab.@mount[$idx].target="/mnt/data"
+			uci -q commit fstab
+		fi
+
+		touch "$p4flag"
+	fi
 
-	# Resize filesystem
-	resize2fs /dev/mmcblk2p3 2>/dev/null
-	touch "$flag"
 	return 0
 }

package/diy/expand-overlay/files/expand-overlay.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 # /etc/uci-defaults/99-expand-overlay
-# Stage 1: Resize partition table to fill unallocated eMMC space.
+# Stage 1: Resize p3 to 3GB, create p4 for Docker data.
 # Auto-removed by uci-defaults after first run.
 
 FLAG_FILE="/etc/expand-overlay.done"
@@ -11,9 +11,19 @@ FLAG_FILE="/etc/expand-overlay.done"
 ROOT_DEV=$(mount | grep ' / ' | awk '{print $1}' | sed 's/p[0-9]*$//')
 [ "$ROOT_DEV" != "/dev/mmcblk2" ] && exit 0
 
-# Save backup, resize partition 3 to fill remaining space
+# Save backup of original partition table
 sfdisk -d /dev/mmcblk2 > /etc/sfdisk.bak 2>/dev/null
-echo ",+" | sfdisk -N 3 /dev/mmcblk2 2>/dev/null
+
+# Step 1: Resize partition 3 to exactly 3GB (3072 MiB)
+#        instead of expanding to fill the entire disk
+echo ",3072M" | sfdisk -N 3 /dev/mmcblk2 2>/dev/null
+
+# Step 2: Create partition 4 using the remaining space
+#         sfdisk -N 4 with ",+" = start after p3, fill to end
+echo ",+" | sfdisk -N 4 /dev/mmcblk2 2>/dev/null
+
+# Step 3: Write RESET marker on p4 so stage 2 knows to format it
+echo "RESET000" | dd of=/dev/mmcblk2p4 bs=512 count=1 conv=notrunc,sync 2>/dev/null
 
 touch "$FLAG_FILE"
 exit 0