Linux设备驱动之阻塞与非阻塞(等待队列)（四）

等待队列在linux驱动程序设计中，可以使用等待队列来实现进程的阻塞，等待队列可以看做保存进程的容器，在阻塞进程时，将进程放入等待队列，当唤醒进程时，从等待队列中取出。等待队列的操作定义等待队列头wait_queue_head_t my_queue初始化等到队列头init_waitqueue_head(&my_queue)定义并初始化等到队列头DECLARE_WAIT_QUEUE_HEAD（my_queue）定义等待队列DECLARE_WAITQUEUE(name，tsk）添加移除等待队列void fastcall add_wait_queue(wait_queue_head_t *q，wait_queue_t *wait）;void fastcall remove_wait_queue(wait_queue_head_t *q,wait_queue_t *wait);有条件睡眠wait_event(queue,condition)  一直睡眠到condition为真，否则进程状态为TASK_UNINTERRUPTIBLE睡眠模式wait_event_interruptible(queue,condition)一直睡眠到condition为真，否则进程状态为TASK_INTERRUPTIBLE睡眠模式等待队列的唤醒wake_up从等待队列中唤醒状态为TASK_UNINTERRUPTIBLE,TASK_INTERRUPTIBLE,TASK_KILLABLE的所有进程wake_up_interruptible从等待队列中唤醒状态为TASK_INTERRUPTIBLE进程驱动代码#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 #include #include #include #include #include #include #include #include #include #include #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,中断信号唤醒 */{        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 */  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 ((newposMEMDEV_SIZE))    return -EINVAL;        filp->f_pos = newpos;    return newpos;}/*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,};/*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     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   {        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));  }     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);读测试程序#include int main(){FILE *fp = NULL;char Buf[128];/*初始化Buf*/strcpy(Buf,"memdev is char dev!");printf("BUF: %s\n",Buf);/*打开设备文件*/fp = fopen("/dev/memdev0","r+");if (fp == NULL){printf("Open memdev0 Error!\n");return -1;}/*清除Buf*/strcpy(Buf,"Buf is NULL!");printf("Read BUF1: %s\n",Buf);/*读出数据*/fread(Buf, sizeof(Buf), 1, fp);/*检测结果*/printf("Read BUF2: %s\n",Buf);fclose(fp);return 0;}写测试程序：#include 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!\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;}（待续）