[Linux内核驱动]轮询操作

轮询操作

关于用户空间的轮询操作，poll，select，epoll等自行查询，这里只简单介绍设备驱动中的poll函数

poll函数一个典型模板：

unsigned int poll_chr_poll_func(struct file* filp, poll_table* wait)
{
 unsigned int mask = 0;
 // 获取设备结构体指针
 struct xxx_dev* dev = filp->private_data;

 ...
 // 分别加入读写等待队列
 poll_wait(filp, &dev->r_wq, wait);
 poll_wait(filp, &dev->w_wq, wait);

 // 可读
 if (...)
 mask |= POLLIN | POLLRDNORM;
 // 可写
 if (...)
 mask |= POLLOUT | POLLWRNORM;

 return mask;
}

这个函数主要进行下面两项工作

• 对可能引起设备文件状态变化的等待队列调用poll_wair()函数，将对应的等待队列头添加到poll_table结构体中
• 返回表示是否能对设备进行无阻赛的读、写访问的掩码

代码

/*
 * @Date: 2024-05-07 15:37:32
 * @author: lidonghang-02 [email protected]
 * @LastEditTime: 2024-05-19 19:20:51
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/poll.h>

#include "poll_chr.h"

#define POLL_CHR_SIZE 0x10
#define POLL_CHR_MAJOR 0
#define POLL_CHR_MINOR 0
#define POLL_CHR_NR_DEVS 1

static int poll_chr_major = POLL_CHR_MAJOR;
static int poll_chr_minor = POLL_CHR_MINOR;
static int poll_chr_nr_devs = POLL_CHR_NR_DEVS;

static struct class* poll_chr_cls;
struct poll_chr_dev
{
 struct cdev cdev;
 struct device* class_dev;
 unsigned int len;
 unsigned char mem[POLL_CHR_SIZE];

 struct mutex mutex;
 wait_queue_head_t r_wq;
 wait_queue_head_t w_wq;
};

static struct poll_chr_dev* poll_chr_devp;

static int poll_chr_open_func(struct inode* inode, struct file* filp)
{
 struct poll_chr_dev* dev = container_of(inode->i_cdev, struct poll_chr_dev, cdev);
 filp->private_data = dev;
 printk(KERN_INFO "poll_chr_open\n");
 return 0;
}

static int poll_chr_release_func(struct inode* inode, struct file* filp)
{
 printk(KERN_INFO "poll_chr_release\n");
 return 0;
}

static ssize_t poll_chr_read_func(struct file* filp, char __user* buf, size_t count, loff_t* f_pos)
{
 struct poll_chr_dev* dev = filp->private_data;
 int ret = 0;
 DECLARE_WAITQUEUE(wait, current);
 mutex_lock(&dev->mutex);
 add_wait_queue(&dev->r_wq, &wait);

 while (dev->len == 0)
 {
 if (filp->f_flags & O_NONBLOCK)
 {
 ret = -EAGAIN;
 goto out_1;
 }
 __set_current_state(TASK_INTERRUPTIBLE);
 mutex_unlock(&dev->mutex);

 schedule();
 if (signal_pending(current))
 {
 ret = -ERESTARTSYS;
 goto out_2;
 }
 mutex_lock(&dev->mutex);
 }

 if (count > dev->len)
 count = dev->len;

 if (copy_to_user(buf, dev->mem, count) != 0)
 ret = -EFAULT;
 else
 {
 dev->len = dev->len - count;
 memcpy(dev->mem, dev->mem + count, dev->len);
 ret = count;
 wake_up_interruptible(&dev->w_wq);
 }

out_1:
 mutex_unlock(&dev->mutex);
out_2:
 remove_wait_queue(&dev->r_wq, &wait);
 set_current_state(TASK_RUNNING);
 return ret;
}

static ssize_t poll_chr_write_func(struct file* filp, const char __user* buf, size_t count, loff_t* f_pos)
{
 int ret = -ENOMEM;
 struct poll_chr_dev* dev = filp->private_data;
 DECLARE_WAITQUEUE(wait, current);

 mutex_lock(&dev->mutex);
 add_wait_queue(&dev->w_wq, &wait);

 while (dev->len == POLL_CHR_SIZE)
 {
 if (filp->f_flags & O_NONBLOCK)
 {
 ret = -EAGAIN;
 goto out_1;
 }

 __set_current_state(TASK_INTERRUPTIBLE);

 mutex_unlock(&dev->mutex);

 schedule();
 if (signal_pending(current))
 {
 ret = -ERESTARTSYS;
 goto out_2;
 }
 mutex_lock(&dev->mutex);
 }
 if (count > POLL_CHR_SIZE - dev->len)
 count = POLL_CHR_SIZE - dev->len;

 if (copy_from_user(dev->mem + dev->len, buf, count))
 ret = -EFAULT;
 else
 {
 dev->len += count;
 wake_up_interruptible(&dev->r_wq);
 ret = count;
 }
out_1:
 mutex_unlock(&dev->mutex);
out_2:
 remove_wait_queue(&dev->w_wq, &wait);
 set_current_state(TASK_RUNNING);
 return ret;
}

static long poll_chr_ioctl_func(struct file* filp, unsigned int cmd, unsigned long arg)
{
 struct poll_chr_dev* dev = filp->private_data;
 int ret = 0;

 // 检查幻数(返回值POSIX标准规定，也用-EINVAL)
 if (_IOC_TYPE(cmd) != POLL_CHR_MAGIC)
 return -ENOTTY;
 // 检查命令编号
 if (_IOC_NR(cmd) > POLL_CHR_MAXNR)
 return -ENOTTY;
 // 检查命令方向，并验证用户空间指针的访问权限。
 if (_IOC_DIR(cmd) & _IOC_READ)
 ret = !access_ok(VERIFY_WRITE, (void __user*)arg, _IOC_SIZE(cmd));
 else if (_IOC_DIR(cmd) & _IOC_WRITE)
 ret = !access_ok(VERIFY_READ, (void __user*)arg, _IOC_SIZE(cmd));

 if (ret)
 return -EFAULT;

 switch (cmd)
 {
 case POLL_CHR_CLEAR:
 mutex_lock(&dev->mutex);
 dev->len = 0;
 memset(dev->mem, 0, POLL_CHR_SIZE);
 mutex_unlock(&dev->mutex);
 break;
 default:
 return -EINVAL;
 }
 return 0;
}

static unsigned int poll_chr_poll_func(struct file* filp, poll_table* wait)
{
 unsigned int mask = 0;
 struct poll_chr_dev* dev = filp->private_data;

 mutex_lock(&dev->mutex);
 poll_wait(filp, &dev->r_wq, wait);
 poll_wait(filp, &dev->w_wq, wait);

 if (dev->len != 0)
 mask |= POLLIN | POLLRDNORM;
 if (dev->len != POLL_CHR_SIZE)
 mask |= POLLOUT | POLLWRNORM;

 mutex_unlock(&dev->mutex);
 return mask;
}

static const struct file_operations poll_chr_fops =
{
 .owner = THIS_MODULE,
 .read = poll_chr_read_func,
 .write = poll_chr_write_func,
 .unlocked_ioctl = poll_chr_ioctl_func,
 .poll = poll_chr_poll_func,
 .open = poll_chr_open_func,
 .release = poll_chr_release_func,
};

static int __init poll_chr_init_module(void)
{
 int ret = 0, i;
 dev_t devno = MKDEV(poll_chr_major, poll_chr_minor);

 if (poll_chr_major)
 ret = register_chrdev_region(devno, poll_chr_nr_devs, "poll_chr");
 else
 {
 ret = alloc_chrdev_region(&devno, poll_chr_minor, poll_chr_nr_devs, "poll_chr");
 poll_chr_major = MAJOR(devno);
 }

 if (ret < 0)
 return ret;

 poll_chr_devp = kzalloc(sizeof(struct poll_chr_dev) * poll_chr_nr_devs, GFP_KERNEL);
 if (!poll_chr_devp)
 {
 printk(KERN_WARNING "alloc mem failed");
 ret = -ENOMEM;
 goto out_1;
 }

 poll_chr_cls = class_create(THIS_MODULE, "poll_chr");
 if (IS_ERR(poll_chr_cls))
 {
 printk(KERN_WARNING "Error creating class for ioctl");
 goto out_2;
 }

 for (i = 0; i < poll_chr_nr_devs; i++)
 {
 cdev_init(&poll_chr_devp[i].cdev, &poll_chr_fops);
 poll_chr_devp[i].cdev.owner = THIS_MODULE;
 ret = cdev_add(&poll_chr_devp[i].cdev, MKDEV(poll_chr_major, poll_chr_minor + i), 1);
 if (ret)
 printk(KERN_WARNING "Error adding cdev for device %d", i);
 else
 {
 poll_chr_devp[i].class_dev = device_create(poll_chr_cls, NULL, MKDEV(poll_chr_major, poll_chr_minor + i), NULL, "poll_chr%d", i);
 if (IS_ERR(poll_chr_devp[i].class_dev))
 printk(KERN_WARNING "Error creating device for device %d", i);
 }
 mutex_init(&poll_chr_devp[i].mutex);
 init_waitqueue_head(&poll_chr_devp[i].r_wq);
 init_waitqueue_head(&poll_chr_devp[i].w_wq);
 }
 return 0;
out_2:
 kfree(poll_chr_devp);
out_1:
 unregister_chrdev_region(devno, poll_chr_nr_devs);
 return ret;
}

static void __exit poll_chr_exit_module(void)
{
 int i;
 for (i = 0; i < poll_chr_nr_devs; i++)
 {
 device_destroy(poll_chr_cls, MKDEV(poll_chr_major, poll_chr_minor + i));
 cdev_del(&poll_chr_devp[i].cdev);
 }
 class_destroy(poll_chr_cls);
 kfree(poll_chr_devp);
 unregister_chrdev_region(MKDEV(poll_chr_major, poll_chr_minor), poll_chr_nr_devs);
 printk(KERN_INFO "poll_chr exit\n");
}

module_param(poll_chr_major, int, S_IRUGO);
module_param(poll_chr_minor, int, S_IRUGO);
module_param(poll_chr_nr_devs, int, S_IRUGO);

module_init(poll_chr_init_module);
module_exit(poll_chr_exit_module);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("lidonghang-02");

#ifndef _POLL_CHR_H_
#define _POLL_CHR_H_

#define POLL_CHR_MAGIC 'c'

#define POLL_CHR_CLEAR _IO(POLL_CHR_MAGIC, 0)

#define POLL_CHR_MAXNR 1

#endif /* _POLL_CHR_H_ */

测试

epoll

/*
 * @Date: 2024-05-12 18:13:03
 * @author: lidonghang-02 [email protected]
 * @LastEditTime: 2024-05-19 19:18:37
 */
#include <sys/time.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <strings.h>

#include <sys/epoll.h>

#include "poll_chr.h"

int main()
{

 int fd = open("/dev/poll_chr0", O_RDONLY | O_NONBLOCK);

 if (fd != -1)
 {
 struct epoll_event ev_poll_chr;
 int err;
 int epfd;
 if (ioctl(fd, POLL_CHR_CLEAR, 0) < 0)
 {
 printf("ioctl error\n");
 return 0;
 }
 epfd = epoll_create(1);
 if (epfd < 0)
 {
 perror("epoll_create()");
 return;
 }

 bzero(&ev_poll_chr, sizeof(struct epoll_event));
 ev_poll_chr.events = EPOLLIN | EPOLLPRI;

 err = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev_poll_chr);
 if (err < 0)
 {
 perror("epoll_ctl1 error");
 return 0;
 }
 err = epoll_wait(epfd, &ev_poll_chr, 1, 10000);
 if (err < 0)
 perror("epoll_wait error");
 else if (err == 0)
 printf("timeout\n");
 else
 printf("not empty\n");

 err = epoll_ctl(epfd, EPOLL_CTL_DEL, fd, &ev_poll_chr);
 if (err < 0)
 perror("epoll_ctl2 error");
 }
 else
 printf("open error\n");
 return 0;
}

select

/*
 * @Date: 2024-05-12 17:31:54
 * @author: lidonghang-02 [email protected]
 * @LastEditTime: 2024-05-19 19:18:40
 */
#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

#include "poll_chr.h"

int main()
{
 fd_set rfds, wfds; /* 读/写文件描述符集 */

 int fd = open("/dev/poll_chr0", O_RDONLY | O_NONBLOCK);
 if (fd != -1)
 {
 if (ioctl(fd, POLL_CHR_CLEAR, 0) < 0)
 printf("ioctl error\n");
 else
 {
 while (1)
 {
 FD_ZERO(&rfds);
 FD_ZERO(&wfds);
 FD_SET(fd, &rfds);
 FD_SET(fd, &wfds);
 select(fd + 1, &rfds, &wfds, NULL, NULL);
 /* 数据可获得 */
 if (FD_ISSET(fd, &rfds))
 printf("Poll monitor:can be read\n");
 /* 数据可写入 */
 if (FD_ISSET(fd, &wfds))
 printf("Poll monitor:can be written\n");
 sleep(1);
 }
 }
 }
 else
 printf("open error\n");
 return 0;
}