Linux字符設備驅動（三）自動創建設備節點

Linux字符設備驅動（三）自動創建設備節點

在前面的字符設備中需要手動運行mknod創建設備節點，但其實linux中可以通過udev自動創建設備節點，通過下面兩步即可實現。

struct class *class_create(struct module *owner,
						  const char *name);
struct device *device_create(struct class *cls, struct device *parent,
			     dev_t devt, void *drvdata,
			     const char *fmt, ...);

其中devce_create中最後一個參數爲創建的設備節點名字。

chrdev03.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>	//class_create
///////////////////////////////////////////////////////
int major=0;
struct class *cls;
struct device *clsdev;
///////////////////////////////////////////////////////
int chrdev03_open(struct inode *inode, struct file *filp)
{
	printk("chrdev03_open.\n");
	return 0;
}
struct file_operations chrdev03_ops = {
	.owner = THIS_MODULE,
	.open  = chrdev03_open,
};
///////////////////////////////////////////////////////
static int __init chrdev03_init(void)
{
	printk("chrdev03_init.\n");
	/* 主設備號設置爲0表示由系統自動分配主設備號 */ 
	major = register_chrdev(0, "chrdev03", &chrdev03_ops);
	if (major<0) {
		printk("register_chrdev failed!\n");
		return -ENOMEM;
	}
	/* cls */  
    cls = class_create(THIS_MODULE, "chrdev03");
    if (IS_ERR(cls)) {
    	printk("class_create failed.\n");
    	goto ERR_CLS_CREATE;
    }
  
    /* 在clsdev類下創建chrdev03設備，供應用程序打開設備*/  
    clsdev = device_create(cls, NULL, MKDEV(major, 0), NULL, "chrdev03");
    if (IS_ERR(clsdev)) {
    	printk("device_create failed.\n");
    	goto ERR_CLSDEV_CREATE;
    }
	return 0;
ERR_CLSDEV_CREATE:
    class_destroy(cls);
ERR_CLS_CREATE:
	unregister_chrdev(major, "chrdev03");
	return -ENOMEM;
}

static void __exit chrdev03_exit(void)
{
	printk("chrdev03_exit.\n");
	device_destroy(cls, MKDEV(major,0));
    class_destroy(cls);
	unregister_chrdev(major, "chrdev03");
}

module_init(chrdev03_init);
module_exit(chrdev03_exit);

MODULE_AUTHOR("Rbin.Yao");
MODULE_VERSION("V1.0");
MODULE_DESCRIPTION("A simple char device.");
MODULE_LICENSE("GPL");

Makefile

obj-m	:= chrdev03.o
PWD		:= $(shell pwd)
KDIR	:= /lib/modules/$(shell uname -r)/build

all: chrdev03_test
	make -C $(KDIR) M=$(PWD) modules
	
clean:
	make -C $(KDIR) M=$(PWD) clean
	rm -f chrdev03_test
	
chrdev03_test:chrdev03_test.c
	gcc $< -o $@
	

chrdev03_test.c

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
int main(int argc, char **argv)
{
	int fd;
	fd = open("/dev/chrdev03", O_RDONLY);
	if (fd<0) {
		perror("open /dev/chrdev03 failed.");
	} else {
		printf("open /dev/chrdev03 ok!\n");
		close(fd);
	}
	
	return 0;
}