一些技巧

How to add permission for device node

By default, other than the devices listed in system/init/device.c, Android will set the device node permission as 600. It means only root can access the device. This will cause many trouble because most of the process runs as system account, not root.

Android notices this issue, so it supports a builtin command named "device" for init script file. The command format is:

device dev_node_name permission user_account group_account

For example, for ALSA device, we can set the permission as:

on early-init

       device /dev/pcmC0D0p 0666 root audio

The device command must be put in early-init action. Otherwise it won't work. Because init will first execute early-init action, then setup device node.

Manually create system.img in Android

You can do it like this to build system.img.

$cd device/out/host/linux-x86/bin

$./mkyaffs2image ../../../target/product/saar/system system.img -f

So that you can manually add more files into system.img.