i try mod the system.img on ubuntu linux with unyaffs and mkfs.yaffs2, i "hacked" the symlinks(because the armv6 unyaffs doen't like) so now everything is ok, unyaffs works well. BUT:
when i flash the other sin files with flashtool, my x8 is restart after a green sony ball. i gave to all file in bin folder: rwx-rx-rx and the all other files got rw-r-r permissions.
so, i don't know what is the problem with this method.
//my system.img was flashed with a method in "clean and pre-rooted 2.1 rom" thread.//
in attachment the filesunyaffs and mkfs.yaffs2.x86)