【Linux设备驱动程序（第三版）】----设备文件的访问控制：独享设备

 【Linux设备驱动程序（第三版）】----设备文件的访问控制：独享设备

complete.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/fs.h>//file_operations, file
#include <linux/completion.h>
#include <asm/uaccess.h>//copy_to_user & copy_from_user

MODULE_LICENSE("Dual BSD/GPL");
#define MEMSIZE 100
int complete_major = 250;
DECLARE_COMPLETION(comp);
unsigned char s[MEMSIZE];
static atomic_t scull_s_available = ATOMIC_INIT(1);

ssize_t complete_read(struct file *filp, char __user *buf, size_t size, loff_t *pos)
{
	#if 0
	unsigned long p = *pos;
	unsigned int count = size;
	int ret = 0;
	if(p >= MEMSIZE)
		return 0;
	if(count > MEMSIZE - p)
		count = MEMSIZE -p;
	wait_for_completion(&comp);
	if(copy_to_user(buf, (void*)(s + p), count)){
		return -EFAULT;
	}
	*pos += count;
	ret = count;
	return ret;
	#endif
	wait_for_completion(&comp);
	return 0;
}

ssize_t complete_write(struct file *filp, char __user *buf, size_t size, loff_t *pos)
{
	#if 0
	unsigned long p = *pos;
	unsigned int count = size;
	int ret = 0;

	if(p >= MEMSIZE)
		return 0;
	if(count > MEMSIZE - p)
		count = MEMSIZE -p;
	if(copy_from_user(s + p, buf, count)){
		return -EFAULT;
	}
	*pos += count;
	ret = count;
	complete(&comp);
	return ret;
	#endif
	return 0;
}

static int complete_open(struct inode *inode, struct file *filp)
{
	printk(KERN_DEBUG "Enter Open......");
	if(!atomic_dec_and_test(&scull_s_available)){
		atomic_inc(&scull_s_available);
		printk(KERN_DEBUG "Busy......");
		return -EBUSY;
	}
	printk(KERN_DEBUG "Open Ok......");
	return 0;
}

static int complete_release(struct inode *inode, struct file *filp)
{
	printk(KERN_DEBUG "Enter Release......");
	atomic_inc(&scull_s_available);
	return 0;
}

struct file_operations complete_fops = {
	.owner = THIS_MODULE,
	.read = complete_read,
	.write = complete_write,
	.open = complete_open,
	.release = complete_release,
};

int complete_init(void)
{	
	printk(KERN_DEBUG "complete_init111......");
	int result;

	result = register_chrdev(complete_major, "complete", &complete_fops);
	if(result < 0)
		return result;
	return 0;
}

void complete_exit(void)
{
	printk(KERN_DEBUG "complete_exit222......");
	unregister_chrdev(complete_major, "complete");
}

module_init(complete_init);
module_exit(complete_exit);

Makefile

obj-m:= complete.o
modules-objs:= complete.o

KDIR:= /usr/src/linux-headers-2.6.31-14-generic/
PWD:= $(shell pwd)

default:
	make -C $(KDIR) M=$(PWD) modules
clean:
	rm -rf *.ko *.mod.c *.mod.o *.o *.markers *.symvers *.order

创建设备节点

mknod /dev/complete c 250 0

装载驱动

insmod complete.ko

测试

打开一终端，输入：

cat /dev/complete

打开另一终端，输入：

cat /dev/complete

此时，终端输出提示：设备正忙。

卸载驱动

rmmod complete