1. 创建字符设备 生成设备节点

2. busybox
Linux System Utilities --->
[*] mdev
[*] Support /etc/mdev.conf
[*] Support command execution at device addition/removal

3. kernel
File systems --->
Pseudo filesystems --->
[*] sysfs file system support
[*] Virtual memory file system support (former shm fs)
[*] Tmpfs POSIX Access Control Lists

4. rootfs
vi ./etc/init.d/rcS
mount -t tmpfs mdev /dev
mkdir /dev/pts
mount -t devpts devpts /dev/pts
mount -t sysfs sysfs /sys
mount -a
echo /sbin/mdev > /proc/sys/kernel/hotplug
mdev -s