Customize google android system.img for emulator

The google android emulator included in the google android sdk is limited. Although you can use 'adb push' to upload more tools, but one has to do it again next time. Follow the steps to create a enhanced system.img:

1. system.img is yaffs2 flash file system, so firstly you need the mkfs.yaffs2 tool, download it in the following link: Release Android Yaffs2 Tool (Both X86 And ARM). One has to be a registered user to download the tools.
2. use the 'adb push' to upload tools to android emulator, executables in /system/bin/, libraries in /system/lib, one can also create folder. One need change the file mode necessary.
3. upload the ARM mkfs.yaffs2 tool, use the following command to create system.img: # mkfs.yaffs2 /system /system.img
4. download the system.img to local with command 'adb pull', replace the system.img in your emulator folder/tools/lib/images/