OpenWrt 18.06.4 SD eMMC image for Banana Pi R2

bpi-r2-sdimage.sh

#!/bin/bash
# OpenWrt 18.06.4 for Banana Pi R2
# Make SD or eMMC image from official kernel and rootfs images.
# Inspired by https://github.com/BPI-SINOVOIP/openwrt/commit/b4dfaeca4d33ad88364bfb7df353b3dfca2883fe

set -e

KIND=$1
if [[ $KIND != sd ]] && [[ $KIND != emmc ]]; then
  echo Usage: $0 '<sd|emmc> [outfile]' >/dev/stderr
  exit 2
fi

OUTFILE=${2:-bpi-r2-$KIND.bin}

MTKBASE=https://github.com/BPI-SINOVOIP/openwrt/raw/b4dfaeca4d33ad88364bfb7df353b3dfca2883fe/staging_dir/target-arm_cortex-a7%2Bneon-vfpv4_musl_eabi/image/
PRELOADER=mtk-bpi-r2-preloader-$KIND.bin
UBOOT=mtk-bpi-r2-uboot.bin

OPENWRTVER=18.06.4
OPENWRTBASE=https://downloads.openwrt.org/releases/$OPENWRTVER/targets/mediatek/mt7623/
KERNEL=openwrt-$OPENWRTVER-mediatek-mt7623-7623n-bananapi-bpi-r2-initramfs-kernel.bin
ROOTFS=openwrt-$OPENWRTVER-mediatek-mt7623-7623n-bananapi-bpi-r2-squashfs-sysupgrade.bin

[[ -f $PRELOADER ]] || wget $MTKBASE/$PRELOADER
[[ -f $UBOOT ]] || wget $MTKBASE/$UBOOT
[[ -f $KERNEL ]] || wget $OPENWRTBASE/$KERNEL
[[ -f $ROOTFS ]] || wget $OPENWRTBASE/$ROOTFS

rm -f $OUTFILE
dd bs=1024 if=$PRELOADER of=$OUTFILE seek=0
dd bs=1024 if=$UBOOT of=$OUTFILE seek=320
dd bs=1024 if=$KERNEL of=$OUTFILE seek=2048
dd bs=1024 if=$ROOTFS of=$OUTFILE seek=67584

Could you please explain, howto calculate the offset for $ROOTFS? Because I created my own kernel and rootfs, I get unusable image, if I replace kernel.bin and sysupgrade.bin by my own.

Could you please explain, howto calculate the offset for $ROOTFS?

Sadly, I don't know. It's copied from the "inspired by" commit.