From e42c7066d7389808a3922330d01e1bf58207f8ff Mon Sep 17 00:00:00 2001
From: Tomaz Zaman <tomaz@mono.si>
Date: Mon, 10 Aug 2026 23:47:28 +0200
Subject: [PATCH 32/77] layerscape: fix first-boot backup GPT write

The first-boot script used 'blockdev --getsz' to size the device, but
blockdev is not in the busybox image - so the size came out empty, the
backup-GPT write was silently skipped, and the uci-default still exited 0
and self-deleted, so it never retried. Use /sys/block/mmcblk0/size (always
present, no tool), make the write idempotent (skip if the EFI PART header is
already at the last LBA), and exit non-zero to retry next boot until the
backup GPT is confirmed - instead of self-deleting on a silent skip.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../10-mono-gateway-expand-rootfs             | 55 ++++++++++---------
 1 file changed, 28 insertions(+), 27 deletions(-)

diff --git a/target/linux/layerscape/base-files/etc/uci-defaults/10-mono-gateway-expand-rootfs b/target/linux/layerscape/base-files/etc/uci-defaults/10-mono-gateway-expand-rootfs
index 814defb48b..fa66a82414 100644
--- a/target/linux/layerscape/base-files/etc/uci-defaults/10-mono-gateway-expand-rootfs
+++ b/target/linux/layerscape/base-files/etc/uci-defaults/10-mono-gateway-expand-rootfs
@@ -4,12 +4,11 @@
 #     inside a partition already sized to the full eMMC (the on-device GPT
 #     is never rewritten by an upgrade, and its entry array sits in the
 #     first 4 KiB clear of the boot firmware; see mono_gpt.py).
-#  2. Write the backup GPT to the end of the device. The flashed image is
-#     trimmed and carries only the primary GPT, so the secondary copy is
-#     laid down here from the blob shipped in the boot partition. This makes
-#     the on-disk table complete so partition tools do not "repair" it.
-# uci-defaults run once and self-delete on exit 0; both steps are idempotent
-# so a re-run after sysupgrade is harmless.
+#  2. Write the backup GPT to the end of the device from the blob shipped in
+#     the boot partition, so the on-disk table is complete and partition
+#     tools do not "repair" it.
+# uci-defaults self-delete on exit 0; this script exits NON-zero (retries
+# next boot) until the backup GPT is confirmed present, and is idempotent.
 . /lib/functions.sh
 
 case "$(board_name)" in
@@ -18,33 +17,35 @@ mono,gateway-dk|mono,gateway-dk-sdboot) ;;
 esac
 
 disk=/dev/mmcblk0
+sysfs=/sys/block/mmcblk0/size          # size in 512-byte sectors (no tools)
 rc=0
 
-# 1. grow rootfs
+# 1. grow rootfs (no-op once full)
 root_dev=$(readlink -f /dev/root 2>/dev/null)
 [ -b "$root_dev" ] || root_dev=/dev/mmcblk0p2
-if ! resize2fs "$root_dev" 2>&1 | logger -t mono-firstboot; then
-	logger -t mono-firstboot "resize2fs failed on $root_dev"
-	rc=1
-fi
+resize2fs "$root_dev" 2>&1 | logger -t mono-firstboot
 
-# 2. lay down the backup GPT from the blob in the boot partition
-if [ -b /dev/mmcblk0p1 ]; then
-	mkdir -p /tmp/bootp
-	if mount -t ext4 -o ro /dev/mmcblk0p1 /tmp/bootp 2>/dev/null; then
-		if [ -f /tmp/bootp/boot/backup-gpt.bin ]; then
-			sectors=$(blockdev --getsz "$disk" 2>/dev/null)
-			if [ -n "$sectors" ]; then
-				dd if=/tmp/bootp/boot/backup-gpt.bin of="$disk" \
-					bs=512 seek=$((sectors - 33)) conv=fsync 2>/dev/null \
-					&& logger -t mono-firstboot "backup GPT written at sector $((sectors - 33))" \
-					|| { logger -t mono-firstboot "backup GPT write failed"; rc=1; }
-			fi
-		fi
-		umount /tmp/bootp 2>/dev/null
+# 2. backup GPT
+sectors=$(cat "$sysfs" 2>/dev/null)
+if [ -z "$sectors" ]; then
+	logger -t mono-firstboot "no $sysfs, deferring backup GPT"
+	rc=1
+elif [ "$(dd if="$disk" bs=512 skip=$((sectors - 1)) count=1 2>/dev/null | head -c 8)" = "EFI PART" ]; then
+	:                                      # already present
+elif [ -b /dev/mmcblk0p1 ] && mkdir -p /tmp/bootp && \
+     mount -t ext4 -o ro /dev/mmcblk0p1 /tmp/bootp 2>/dev/null; then
+	if [ -f /tmp/bootp/boot/backup-gpt.bin ] && \
+	   dd if=/tmp/bootp/boot/backup-gpt.bin of="$disk" \
+	      bs=512 seek=$((sectors - 33)) conv=fsync 2>/dev/null; then
+		logger -t mono-firstboot "backup GPT written at sector $((sectors - 33))"
+	else
+		logger -t mono-firstboot "backup GPT write failed"
+		rc=1
 	fi
-	rmdir /tmp/bootp 2>/dev/null
+	umount /tmp/bootp 2>/dev/null
+else
+	logger -t mono-firstboot "cannot mount boot partition, deferring backup GPT"
+	rc=1
 fi
 
-# Non-zero keeps this script for a retry next boot.
 exit $rc
-- 
2.47.3