[Kernel Module] My first Kernel Module

Kernel Code 1

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
static ssize_t drv_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
{
    printk("device read\n");
    return count;
}

static ssize_t drv_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
{
    printk("device write \n");
    return count;
}

static int drv_open(struct inode *inode, struct file *filp)
{
    printk("device open \n");
    return 0;
}


int drv_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
    printk("device ioctl \n");
    return 0;
}

static int drv_release(struct inode *inode, struct file *filp)
{
    printk("device close \n");
    return 0;
}

struct file_operations drv_fops = 
{
    read:               drv_read,       
    write:              drv_write,      
    compat_ioctl:       drv_ioctl,      
    open:               drv_open,       
    release:            drv_release,
};

#define MAJOR_NUM 60
#define MODULE_NAME "DEMO"
static int demo_init(void) {
 if (register_chrdev(MAJOR_NUM, "demo", &drv_fops) < 0) {
        printk("<1>%s: can't get major %d\n", MODULE_NAME, MAJOR_NUM);
            return (-EBUSY);
    }

    printk("<1>%s:started\n", MODULE_NAME);
    return 0;
}

static void demo_exit(void) {
        unregister_chrdev(MAJOR_NUM, "demo");
        printk("<1>%s: removed\n", MODULE_NAME);
}

module_init(demo_init);
module_exit(demo_exit);

Compile Kernel Module

make -C /lib/modules/3.8.0-33-generic/build M=`pwd` test.ko

User Space Code

#include <stdio.h>
int main()
{
char buf[512];
FILE *fp = fopen("/dev/demo", "w+");
if(fp == NULL) {
    printf("can't open device!\n");
    return 0;
}
fread(buf, sizeof(buf), 1, fp);
fwrite(buf, sizeof(buf), 1, fp);
fclose(fp);
return 0;
}

Compile User Space Code

gcc test.c

Execute Code

sudo ./a.out

Result

tail -n 10 /var/log/kern.log
Jul  3 12:14:36 happy-Desktop kernel: [12404.120783] device close 
Jul  3 12:14:37 happy-Desktop kernel: [12405.044410] device open 
Jul  3 12:14:37 happy-Desktop kernel: [12405.044447] device read
Jul  3 12:14:37 happy-Desktop kernel: [12405.044477] device close 
Jul  3 12:14:38 happy-Desktop kernel: [12406.056777] device open 
Jul  3 12:14:38 happy-Desktop kernel: [12406.056814] device read
Jul  3 12:14:38 happy-Desktop kernel: [12406.056839] device close 
Jul  3 12:15:10 happy-Desktop kernel: [12438.189191] device open 
Jul  3 12:15:10 happy-Desktop kernel: [12438.189233] device read
Jul  3 12:15:10 happy-Desktop kernel: [12438.189262] device close 

---

1. 第一次寫Linux Driver就上手 - RSWiki ↩