国嵌内核驱动进阶班-7-4（Poll设备方法）

Poll 与系统select调用相对应

int select(int nfds, fd_set *readfds, fd_set *writefds,
　　fd_set *exceptfds, struct timeval *timeout)

 

---

Poll设备方法完成流程：

1. 使用poll_wait将等待队列添加到poll_table中

2. 返回描述设备的可读可写的设备掩码。

※ 掩码有：

POLLIN

设备可读

POLLRDNORM

数据可读

POLLOUT

设备可写

POLLWRNORM

数据可写

---

内核代码：

do_select()实现阻塞。

---

#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 <linux/slab.h>
#include <asm/uaccess.h>

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

static int 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 %ld
", 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 %ld
", 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)
{
    unsigned int mask = 0;
    struct mem_dev  *dev = filp->private_data; 
 
    printk(KERN_INFO "@@@@ mytest mem_poll() have_data = %d
", have_data);

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

#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_ */

ifneq ($(KERNELRELEASE),)

obj-m := memdev.o

else
    
KDIR := /home/rpi/RpiLinux
all:
    make -C $(KDIR) M=$(PWD) modules ARCH=arm CROSS_COMPILE=/home/rpi/RpiTools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-bcm2708hardfp-linux-gnueabi-

clean:
    rm -f *.ko *.o *.mod.o *.mod.c *.symvers  modul*

endif

测试代码：

#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 memdev0 Error!
");
        return -1;
    }
    
    /*写入设备*/
    strcpy(Buf,"memdev is char dev!");
    printf("Write BUF: %s
",Buf);
    fwrite(Buf, sizeof(Buf), 1, fp);
    
    sleep(5);
    fclose(fp);
    
    return 0;    

}

#include <stdio.h>

int main()
{
    FILE *fp = NULL;
    char Buf[128];
    
    /*初始化Buf*/
    strcpy(Buf,"memdev is char dev!");
    printf("BUF: %s
",Buf);
    
    /*打开设备文件*/
    fp = fopen("/dev/memdev0","r+");
    if (fp == NULL)
    {
        printf("Open memdev0 Error!
");
        return -1;
    }
    
    /*清除Buf*/
    strcpy(Buf,"Buf is NULL!");
    printf("Read BUF1: %s
",Buf);
    
    /*读出数据*/
    fread(Buf, sizeof(Buf), 1, fp);
    
    /*检测结果*/
    printf("Read BUF2: %s
",Buf);
    
    fclose(fp);
    
    return 0;    

}