Linux: 最小的设备驱动程序框架

1) 最小框架

/* Example Minimal Character Device Driver */
#include <linux/module.h>

static int __init hello_init(void)
{
    printk("Hello Example Init/n");
    return 0;
}
static void __exit hello_exit(void)
{
    printk("Hello Example Exit/n");
}

module_init(hello_init);
module_exit(hello_exit);

MODULE_AUTHOR("OOO");
MODULE_DESCRIPTION("Hello Example");
MODULE_LICENSE("GPL");

2) 增加调用接口

/* Example Minimal Character Device Driver */
#include <linux/module.h>
#include <linux/fs.h>

#define HELLO_MAJOR 242

static int debug_enable = 0;
module_param(debug_enable, int, 0);
MODULE_PARM_DESC(debug_enable, "Enable module debug mode.");

struct file_operations hello_fops;

static int hello_open(struct inode *inode, struct file *file)
{
    printk("hello_open: successful/n");
	return 0;
}

static int hello_release(struct inode *inode, struct file *file)
{
    printk("hello_release: successful/n");
	return 0;
}

static ssize_t hello_read(struct file *file, char *buf, size_t count, loff_t *ptr)
{
	printk("hello_read: returning zero bytes/n");
	return 0;
}

static ssize_t hello_write(struct file *file, const char *buf, size_t count, loff_t *ppos)
{
	printk("hello_write: accepting zero bytes/n");
	return 0;
}

static int hello_ioctl(struct inode *inode, struct file *file, 
                     unsigned int cmd, unsigned long arg)
{
	printk("hello_ioctl: cmd=%d, arg=%ld/n", cmd, arg);
	return 0;
}

static int __init hello_init(void)
{
	int ret;
    printk("Hello Example Init - debug mode is %s/n",
            debug_enable ? "enabled" : "disabled");
	ret = register_chrdev(HELLO_MAJOR, "hello", &hello_fops);
	if(ret < 0) {
		printk("Error registering hello device/n");
		goto hello_fail; 	
	}
	printk("Hello: registered module successfully!/n");

	/* Init processing here... */
	
    return 0;

hello_fail:
	return ret;
}

static void __exit hello_exit(void)
{
    printk("Hello Exaple Exit/n");
}

struct file_operations hello_fops = {
	owner:		THIS_MODULE,
	read:		hello_read,
	write:		hello_write,
	ioctl:		hello_ioctl,
	open:		hello_open,
	release:	hello_release,
};

module_init(hello_init);
module_exit(hello_exit);

MODULE_DESCRIPTION("Hello Module Example");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("OOO");

在linux源码树添加相关配置文件，生成hello.ko，安装到/lib/modules

3) 测试该模块

在目标平台上，

# insmod hello.ko

创建设备节点，比如/dev/hello

# mknod /dev/hello c 242 0

然后，编写测试程序:

/* test hello.ko 
*	 you should insmod hello.ko and mknod /dev/hello before 
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char **argv)
{
	int fd;
	int rc = 0;
	char *rd_buf[16];

	printf("%s: entered/n", argv[0]);

	fd = open("/dev/hello", O_RDWR);
	if(fd == -1) {
		printf("open failed");
		rc = fd;
		exit(-1);	
	}
	printf("%s: open successful: %d/n", argv[0], fd);
	close(fd);

}

交叉编译后，bin档(比如hello-test)放到rootfs/bin目录，在目标平台上运行

# hello-test