1. 引入標頭檔

在撰寫 driver 前必須先 include 一些標頭檔:

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
2. 撰寫控制元件的函式

struct file_operations 即為定義各個 function pointer 的 structure。

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,
ioctl: drv_ioctl,
open: drv_open,
release: drv_release,
};
3. 撰寫初始化、結束元件的函式
#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);

其中 MAJOR_NUM 即為 driver 所對應的 device 的 major number

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