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CHANGE_ROOTFS_IMAGE.md

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How to change the ROOTFS squashfs image

  • extract ROOTFS
  • change the files
  • create a new image

First, it is important that you have a ROOTFS.bin. Either from the tf_update.img or from your own reading of the partition or the flash chip.

see:

  • how to extract tf_recovery.img or tf_update.img
  • how to dump the flash
  • how to tead the flash with ch341a

If you have th ROOTFS.bin, you can extract the whole camera filesystem with a few commands. At first change the dir to your FW-Image and then run:

$ unsquashfs ROOTFS.bin

This will create a directory squashfs-root with the content of the read only partition of the camera linux system. But now you can modifiy it.

$ ls -a  squashfs-root/
.   bin     data          dev  lib    linuxrc  mnt       opt   root  sbin  tmp         usr
..  config  default.prop  etc  lib32  media    mstar_ko  proc  run   sys   ueventd.rc  var

You can change the content freely or use my patch-scripts. Important are the directories etc/init.d/, bin and etc itself.

After changing the Squashfs partition, you can repack it as follows:

$ mksquashfs squashfs-root/ NEW_ROOTFS.bin -noappend  -comp xz

Now you have a modified RootFS image. However, since the memory area of the flash is larger than the created file, we have to extend it. This is done as follows:

dd if=/dev/zero of=./NEW_ROOTFS.bin bs=1 count=$(( 7733248 - $(stat -c%s ./NEW_ROOTFS.bin) )) seek=$(stat -c%s ./NEW_ROOTFS.bin)

This will fill your RootFS file up to 7733248 bytes.