Open source base system

Package	Progress	Comment
u-boot	WIP	release
kernel	WIP	mainline stable
busybox	Working	rootfs

Reverse engineering upgrade.bin

https://github.com/OpenNoah/NoahSplit

Package	Comment
upgrade.bin extraction	Can extract sections, can extract ubifs images.
upgrade.bin creation	Can generate upgrade.bin, has checksum support.
Customised upgrade	By modifying initramfs packed in the upgrade kernel.

Extract ubifs images

1. Use the rough unubirefimg code I reversed from ubirefimg to convert binary sections back to ubifs images

unubirefimg rootfs.bin rootfs.img

https://github.com/OpenNoah/mtd-utils/blob/master/ubi-utils/new-utils/src/unubirefimg.c

2. Use ubidump to extract files from ubifs images

sudo python ./ubidump.py --savedir rootfs -p rootfs.img

https://github.com/nlitsme/ubidump

Cross debootstrap

https://wiki.debian.org/EmDebian/CrossDebootstrap#QEMU.2Fdebootstrap_approach

# Create rootfs image of size 1GiB
dd if=/dev/null of=rootfs_debian.img bs=4M seek=256
# Format rootfs image to ext4
mkfs.ext4 -F rootfs_debian.img
# Mount rootfs image
mkdir rootfs_debian
mount -t ext4 rootfs_debian.img rootfs_debian
# Create base system
qemu-debootstrap --arch mipsel stretch rootfs_debian http://deb.debian.org/debian/