udev创建linux设备节点

=== udev
在设备被发现时自动加载对应驱动模块。(热插拔，设备被发现时，自动创建dev文件，并加载驱动模块)
1.    vim /udev/Makefile    修改 安装路径和编译器
    prefix = /nfsroot/
    CROSS_COMPILE = /usr/local/arm/3.4.1/bin/arm-linux-

    make
    make install

2.    vim /nfsroot/etc/init.d/rcS 加上
    mount -t tmpfs tmpfs /dev
    /sbin/udevd -d
    /sbin/udevstart
    开机自动挂载

    ------------------ src -------------------------
    init:
        struct cdev my_cdev;
        struct class *my_class;
        #define DUMMY_MAJOR 255
        #define DUMMY_MINOR 0

        dev_t devno = MKDEV(DUMMY_MAJOR, DUMMY_MINOR);

        cdev_init(&my_cdev, &f_ops);
        cdev_add(&my_cdev, MKDEV(DUMMY_MAJOR, DUMMY_MINOR), 1);

        my_class =class_create(THIS_MODULE, "my_class");
        class_device_create(my_class, MKDEV(DUMMY_MAJOR, DUMMY_MINOR), NULL,"my_dev");

    exit:
        cdev_del(&my_cdev);
        class_device_destroy(my_class, MKDEV(DUMMY_MAJOR, DUMMY_MINOR));
        class_destroy(my_class);

#include <stdio.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(void)
{
    int fd;
    fd = open("/dev/test_udev", O_RDWR);
    if(fd < 0)
    {
        printf("open failed\n");
    }

    return 0;
}

#include <linux/module.h>
#include <linux/init.h>

#include <linux/fs.h>
#include <linux/cdev.h>

#include <linux/device.h>

dev_t devno;
struct cdev my_cdev;
struct class *my_class;

int my_open(struct inode *nod, struct file *filp)
{
    printk(" my_open\n");
    return 0;
}
struct file_operations my_ops = {
    .open = my_open,
};

int init_test(void)
{

    devno = MKDEV(253, 0);
    register_chrdev_region(devno, 1, "test udev");
    cdev_init(&my_cdev, &my_ops);

    //init
    my_class = class_create(THIS_MODULE, "test_udev_class");
    device_create(my_class, NULL, devno, NULL, "%s", "test_udev");

    cdev_add(&my_cdev, devno, 1);
    printk("hello udev\n");
    return 0;
}

void exit_test(void)
{
    cdev_del(&my_cdev);
    device_destroy(my_class, devno);
    class_destroy(my_class);
    unregister_chrdev_region(devno, 1);
    printk("bye\n");
}

module_init(init_test);
module_exit(exit_test);

MODULE_LICENSE("GPL");

MODULE_AUTHOR("Richard");
MODULE_DESCRIPTION("this is first module");
MODULE_VERSION("v0.1");