字符设备驱动poll函数

    
       
        
         #ifndef _MEMDEV_H_
 #define _MEMDEV_H_

 #ifndef MEMDEV_MAJOR
 #define MEMDEV_MAJOR 0 /*预设的mem的主设备号*/
 #endif

 #ifndef MEMDEV_NR_DEVS
 #define MEMDEV_NR_DEVS 2 /*设备数*/
 #endif

 #ifndef MEMDEV_SIZE
 #define MEMDEV_SIZE 4096
 #endif

 /*mem设备描述结构体*/
 struct mem_dev
 {
   char *data;
   unsigned long size;
   wait_queue_head_t inq;
 };

 #endif /* _MEMDEV_H_ */ 
        
        
         #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/fs.h>
 #include <linux/errno.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/init.h>
 #include <linux/cdev.h>
 #include <asm/io.h>
 #include <asm/system.h>
 #include <asm/uaccess.h>

 #include <linux/poll.h>
 #include "memdev.h"

 static mem_major = MEMDEV_MAJOR;
 bool have_data = false; /*表明设备有足够数据可供读*/

 module_param(mem_major, int, S_IRUGO);

 struct mem_dev *mem_devp; /*设备结构体指针*/

 struct cdev cdev;

 /*文件打开函数*/
 int mem_open(struct inode *inode, struct file *filp)
 {
     struct mem_dev *dev;

     /*获取次设备号*/
     int num = MINOR(inode->i_rdev);

     if (num >= MEMDEV_NR_DEVS)
             return -ENODEV;
     dev = &mem_devp[num];

     /*将设备描述结构指针赋值给文件私有数据指针*/
     filp->private_data = dev;

     return 0;
 }

 /*文件释放函数*/
 int mem_release(struct inode *inode, struct file *filp)
 {
   return 0;
 }

 /*读函数*/
 static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
 {
   unsigned long p = *ppos;
   unsigned int count = size;
   int ret = 0;
   struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/

   /*判断读位置是否有效*/
   if (p >= MEMDEV_SIZE)
     return 0;
   if (count > MEMDEV_SIZE - p)
     count = MEMDEV_SIZE - p;

   while (!have_data) /* 没有数据可读，考虑为什么不用if，而用while */
   {
         if (filp->f_flags & O_NONBLOCK)
             return -EAGAIN;

     wait_event_interruptible(dev->inq,have_data);
   }

   /*读数据到用户空间*/
   if (copy_to_user(buf, (void*)(dev->data + p), count))
   {
     ret = - EFAULT;
   }
   else
   {
     *ppos += count;
     ret = count;

     printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
   }

   have_data = false; /* 表明不再有数据可读 */
   /* 唤醒写进程 */
   return ret;
 }

 /*写函数*/
 static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
 {
   unsigned long p = *ppos;
   unsigned int count = size;
   int ret = 0;
   struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/

   /*分析和获取有效的写长度*/
   if (p >= MEMDEV_SIZE)
     return 0;
   if (count > MEMDEV_SIZE - p)
     count = MEMDEV_SIZE - p;

   /*从用户空间写入数据*/
   if (copy_from_user(dev->data + p, buf, count))
     ret = - EFAULT;
   else
   {
     *ppos += count;
     ret = count;

     printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
   }

   have_data = true; /* 有新的数据可读 */

     /* 唤醒读进程 */
     wake_up(&(dev->inq));

   return ret;
 }

 /* seek文件定位函数 */
 static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
 {
     loff_t newpos;

     switch(whence) {
       case 0: /* SEEK_SET */
         newpos = offset;
         break;

       case 1: /* SEEK_CUR */
         newpos = filp->f_pos + offset;
         break;

       case 2: /* SEEK_END */
         newpos = MEMDEV_SIZE -1 + offset;
         break;

       default: /* can't happen */
         return -EINVAL;
     }
     if ((newpos<0) || (newpos>MEMDEV_SIZE))
         return -EINVAL;

     filp->f_pos = newpos;
     return newpos;

 }

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

    /*将等待队列添加到poll_table */
     poll_wait(filp, &dev->inq, wait);


     if (have_data) mask |= POLLIN | POLLRDNORM; /* readable */

     return mask;
 }


 /*文件操作结构体*/
 static const struct file_operations mem_fops =
 {
   .owner = THIS_MODULE,
   .llseek = mem_llseek,
   .read = mem_read,
   .write = mem_write,
   .open = mem_open,
   .release = mem_release,
   .poll = mem_poll,
 };

 /*设备驱动模块加载函数*/
 static int memdev_init(void)
 {
   int result;
   int i;

   dev_t devno = MKDEV(mem_major, 0);

   /* 静态申请设备号*/
   if (mem_major)
     result = register_chrdev_region(devno, 2, "memdev");
   else /* 动态分配设备号 */
   {
     result = alloc_chrdev_region(&devno, 0, 2, "memdev");
     mem_major = MAJOR(devno);
   }

   if (result < 0)
     return result;

   /*初始化cdev结构*/
   cdev_init(&cdev, &mem_fops);
   cdev.owner = THIS_MODULE;
   cdev.ops = &mem_fops;

   /* 注册字符设备 */
   cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);

   /* 为设备描述结构分配内存*/
   mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
   if (!mem_devp) /*申请失败*/
   {
     result = - ENOMEM;
     goto fail_malloc;
   }
   memset(mem_devp, 0, sizeof(struct mem_dev));

   /*为设备分配内存*/
   for (i=0; i < MEMDEV_NR_DEVS; i++)
   {
         mem_devp[i].size = MEMDEV_SIZE;
         mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
         memset(mem_devp[i].data, 0, MEMDEV_SIZE);

       /*初始化等待队列*/
      init_waitqueue_head(&(mem_devp[i].inq));
      //init_waitqueue_head(&(mem_devp[i].outq));

   }

   return 0;

   fail_malloc:
   unregister_chrdev_region(devno, 1);

   return result;
 }

 /*模块卸载函数*/
 static void memdev_exit(void)
 {
   cdev_del(&cdev); /*注销设备*/
   kfree(mem_devp); /*释放设备结构体内存*/
   unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
 }

 MODULE_AUTHOR("David Xie");
 MODULE_LICENSE("GPL");

 module_init(memdev_init);
 module_exit(memdev_exit); 
        
        
         #include <stdio.h>

 int main()
 {
     FILE *fp = NULL;
     char Buf[128];

     /*打开设备文件*/
     fp = fopen("/dev/memdev0","r+");
     if (fp == NULL)
     {
         printf("Open Dev memdev Error!\n");
         return -1;
     }

     /*写入设备*/
     strcpy(Buf,"memdev is char dev!");
     printf("Write BUF: %s\n",Buf);
     fwrite(Buf, sizeof(Buf), 1, fp);

     sleep(5);
     fclose(fp);

     return 0;

 } 
        
        
         #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <sys/select.h>
 #include <sys/time.h>
 #include <errno.h>

 int main()
 {
     int fd;
     fd_set rds;
     int ret;
     char Buf[128];

     /*初始化Buf*/
     strcpy(Buf,"memdev is char dev!");
     printf("BUF: %s\n",Buf);

     /*打开设备文件*/
     fd = open("/dev/memdev0",O_RDWR);

     FD_ZERO(&rds);
     FD_SET(fd, &rds);

     /*清除Buf*/
     strcpy(Buf,"Buf is NULL!");
     printf("Read BUF1: %s\n",Buf);

     ret = select(fd + 1, &rds, NULL, NULL, NULL);
     if (ret < 0)
     {
      printf("select error!\n");
      exit(1);
     }
     if (FD_ISSET(fd, &rds))
      read(fd, Buf, sizeof(Buf));

     /*检测结果*/
     printf("Read BUF2: %s\n",Buf);

     close(fd);

     return 0;
 }