字符设备学习笔记

　1.首先构造file_operations结构体，并写出相关函数

static struct file_operations first_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = first_drv_open, 
.write    =    first_drv_write,    
};

　2.编写init函数，函数实现注册字符设备，创建类、设备，ioremap

static int first_drv_init(void)
{
    major = register_chrdev(0, "first_drv", &first_drv_fops); // 注册, 告诉内核

    firstdrv_class = class_create(THIS_MODULE, "firstdrv");

    firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL, "xyz"); /* /dev/xyz */

    gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
    gpfdat = gpfcon + 1;

    return 0;
}

3.编写exit函数，卸载字符设备、类、设备、iounmap

static void first_drv_exit(void)
{
    unregister_chrdev(major, "first_drv"); // 卸载

    class_device_unregister(firstdrv_class_dev);
    class_destroy(firstdrv_class);
    iounmap(gpfcon);
}

4.修饰init、exit函数，GPL协议

module_init(first_drv_init);
module_exit(first_drv_exit);


MODULE_LICENSE("GPL");

5.示例

 1 #include <linux/module.h>
 2 #include <linux/kernel.h>
 3 #include <linux/fs.h>
 4 #include <linux/init.h>
 5 #include <linux/delay.h>
 6 #include <asm/uaccess.h>
 7 #include <asm/irq.h>
 8 #include <asm/io.h>
 9 #include <asm/arch/regs-gpio.h>
10 #include <asm/hardware.h>
11 
12 static struct class *firstdrv_class;
13 static struct class_device    *firstdrv_class_dev;
14 
15 volatile unsigned long *gpfcon = NULL;
16 volatile unsigned long *gpfdat = NULL;
17 
18 
19 static int first_drv_open(struct inode *inode, struct file *file)
20 {
21     //printk("first_drv_open\n");
22     /* 配置GPF4,5,6为输出 */
23     *gpfcon &= ~((0x3<<(4*2)) | (0x3<<(5*2)) | (0x3<<(6*2)));
24     *gpfcon |= ((0x1<<(4*2)) | (0x1<<(5*2)) | (0x1<<(6*2)));
25     return 0;
26 }
27 
28 static ssize_t first_drv_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
29 {
30     int val;
31 
32     //printk("first_drv_write\n");
33 
34     copy_from_user(&val, buf, count); //    copy_to_user();
35 
36     if (val == 1)
37     {
38         // 点灯
39         *gpfdat &= ~((1<<4) | (1<<5) | (1<<6));
40     }
41     else
42     {
43         // 灭灯
44         *gpfdat |= (1<<4) | (1<<5) | (1<<6);
45     }
46     
47     return 0;
48 }
49 
50 static struct file_operations first_drv_fops = {
51     .owner  =   THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
52     .open   =   first_drv_open,     
53     .write    =    first_drv_write,       
54 };
55 
56 
57 int major;
58 static int first_drv_init(void)
59 {
60     major = register_chrdev(0, "first_drv", &first_drv_fops); // 注册, 告诉内核
61 
62     firstdrv_class = class_create(THIS_MODULE, "firstdrv");
63 
64     firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL, "xyz"); /* /dev/xyz */
65 
66     gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
67     gpfdat = gpfcon + 1;
68 
69     return 0;
70 }
71 
72 static void first_drv_exit(void)
73 {
74     unregister_chrdev(major, "first_drv"); // 卸载
75 
76     class_device_unregister(firstdrv_class_dev);
77     class_destroy(firstdrv_class);
78     iounmap(gpfcon);
79 }
80 
81 module_init(first_drv_init);
82 module_exit(first_drv_exit);
83 
84 
85 MODULE_LICENSE("GPL");

 6.测试程序

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

/* firstdrvtest on
  * firstdrvtest off
  */
int main(int argc, char **argv)
{
    int fd;
    int val = 1;
    fd = open("/dev/xyz", O_RDWR);
    if (fd < 0)
    {
        printf("can't open!\n");
    }
    if (argc != 2)
    {
        printf("Usage :\n");
        printf("%s <on|off>\n", argv[0]);
        return 0;
    }

    if (strcmp(argv[1], "on") == 0)
    {
        val  = 1;
    }
    else
    {
        val = 0;
    }
    
    write(fd, &val, 4);
    return 0;
}