mediatek: filogic: wax220: support factory image

Enable building a factory image which can be flashed through the OEM
firmware's web interface. It seems that the web interface requires a
minimum file size of 10MiB, otherwise it will not accept the image.

The update image is a regular sysupgrade tarball packed in a Netgear
encrypted image. The Netgear encrypted image is the same as used in
WAX202 or WAX206, including the encryption keys and IV.

This adds a script which creates the rootfs_data volume on first
startup. This is required since the OEM firmware's sysupgrade scripts
do not create such a paritition. Note that any script ordered after
70_initramfs_test will not get executed on initramfs. Hence this new
script 75_rootfs_prepare won't create the rootfs_data volume when
using the recovery initramfs.

Also, this deletes the kernel_backup and rootfs_backup volumes in case
we have to create the rootfs_data volumes. This makes sure that
OpenWrt is the actual backup firmware instead of the stock firmware.

References in WAX220 GPL source:
https://www.downloads.netgear.com/files/GPL/WAX220-V1.0.2.8-gpl-src.tar.gz

* package/base-files/files/lib/upgrade/nand.sh:186
  Creation of rootfs_data is disabled

* Uboot-upstream/board/mediatek/common/ubi_helper.c
  Automatic creation of UBI backup volumes

Signed-off-by: Stefan Agner <stefan@agner.ch>
(cherry picked from commit fa9d977f979461628161085dcd0e9dd8b9e2c66b)

1 files changed, 35 insertions, 0 deletions

diff --git a/target/linux/mediatek/filogic/base-files/lib/preinit/75_rootfs_prepare b/target/linux/mediatek/filogic/base-files/lib/preinit/75_rootfs_prepare
new file mode 100644
index 0000000000..0a32073e0b
--- /dev/null
+++ b/target/linux/mediatek/filogic/base-files/lib/preinit/75_rootfs_prepare
@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
+
+rootfs_create() {
+	local blocks
+
+	blocks=$(cat /sys/class/ubi/ubi0/avail_eraseblocks)
+	[ -z "$blocks" ] && {
+		echo "Failed to read amount of available erase blocks" >&2
+		return
+	}
+
+	# Delete after getting available blocks: Make sure enough space is
+	# left to recreate these volumes.
+	ubirmvol /dev/ubi0 -N kernel_backup
+	ubirmvol /dev/ubi0 -N rootfs_backup
+
+	# Use 90% of remaining flash size for "rootfs_data"
+	ubimkvol /dev/ubi0 -n 20 -N rootfs_data --lebs $((blocks / 100 * 90))
+	mknod -m 0600 /dev/ubi0_20 c 250 21
+}
+
+rootfs_prepare() {
+	case $(board_name) in
+	netgear,wax220)
+		if ! ubinfo /dev/ubi0 -N rootfs_data &>/dev/null; then
+			echo "Creating \"rootfs_data\" UBI volume"
+			rootfs_create
+		fi
+		;;
+	*)
+		;;
+	esac
+}
+
+boot_hook_add preinit_main rootfs_prepare