Modifying the root filesystem on the WRP400 requires a number of steps:

• UnpackTheFirmware
• Extract the squashfs filesystem out of the full rootfs image

The unsquashfs tool can be found in the Result/fullimage/tools/gpl_src/squashfs-tools directory of the source distribution.

 unsquashfs -d rootfs rootfs.bin

• Modify the files in the extracted squashfs filesystem

Modify the files in-place in the rootfs directory, or copy new files into that area from the build directories.

• Rebuild the squahsfs filesystem image

The mksquashfs tool can be found in the Result/fullimage/tools directory of the source distribution. It requires the following options:

 mksquashfs rootfs rootfs-new.bin -noappend -le -noI -force-uid 0 -force-gid 0

• Copy or rebuild the kernel

 cp kernel.bin kernel-new.bin

• Repack the firmware

The mkimage tool can be found in the Result/fullimage/tools directory of the source distribution. It requires the following options:

 mkimage -A arm -O linux -T multi -C none -a 0x00008000 -e 0x00008000 -n cybertan_rom_bin -d kernel-new.bin:rootfs-new.bin cybertan_rom_bin_new.img

There is a Makefile in http://svn.nslu2-linux.org/svnroot/unwrapped/trunk/Makefile which automates these steps.