字符设备驱动和等待队列样例

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <linux/wait.h>
#include <linux/semaphore.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>

#include <linux/socket.h>
#include <linux/tcp.h>
#include <linux/proc_fs.h>
#include <net/net_namespace.h>

#include <net/tcp.h>


static ssize_t globalvar_read(struct file *, char *, size_t, loff_t*);
static ssize_t globalvar_write(struct file *, const char *, size_t, loff_t*);

struct file_operations globalvar_fops =
{
	.owner     = THIS_MODULE,
	.read = globalvar_read,
	.write = globalvar_write,
};

#define LEN 1024
static char global_var[LEN];
static int read_index = 0;
static int write_index = 0;
static spinlock_t var_lock;
static wait_queue_head_t waitq;
static int flag = 0;
static int major;

static const char procname[] = "testvar";

static int __init globalvar_init(void)
{
	init_waitqueue_head(&waitq);
	spin_lock_init(&var_lock);
//    if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &globalvar_fops)) {
	if (!(major = register_chrdev(0, "globalvar", &globalvar_fops))) {
		printk("globalvar register failure\n");
		return -1;
	}
	printk("major = %d\n", major);
	return 0;
}

static void __exit globalvar_exit(void)
{
//    proc_net_remove(&init_net, procname);
	unregister_chrdev(major, "globalvar");
}

static ssize_t globalvar_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
	int read_len;
	//等待数据可获得
	if (wait_event_interruptible(waitq, flag != 0))
		return -ERESTARTSYS;

	spin_lock(&var_lock);
	read_len = write_index - read_index;
	if (copy_to_user(buf, global_var+read_index, read_len)) {
		spin_unlock(&var_lock);
		return -EFAULT;
	}
	read_index = write_index;
	flag = 0;
	spin_unlock(&var_lock);
	return read_len;
}

static ssize_t globalvar_write(struct file *filp, const char *buf, size_t len, loff_t *off)
{
	spin_lock(&var_lock);
	if (copy_from_user(global_var+write_index, buf, len)) {
		spin_unlock(&var_lock);
		return -EFAULT;
	}
	write_index += len;
	spin_unlock(&var_lock);

	flag = 1;
	//通知数据可获得
	wake_up_interruptible(&waitq);
	return len;
}

module_init(globalvar_init);
module_exit(globalvar_exit);
MODULE_LICENSE("GPL");

obj-m += waitqueue.o

PWD = $(shell pwd)
KERNEL := /lib/modules/`uname -r`/build

all:
	make -C $(KERNEL) M=$(PWD) modules

insmod ./waitqueue.ko

$ cat /proc/devices | grep globalvar
$ 249 globalvar

mknod /dev/globalvar c 249 0

cat /dev/globalvar

echo 123 > /dev/globalvar
echo 1234567 > /dev/globalvar
echo 123 > /dev/globalvar