字符设备驱动小计

#include <linux/module.h>#include <linux/slab.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>#define GLOBALMEM_SIZE    0x1000    /*全局内存最大4K字节*/#define MEM_CLEAR 0x1  /*清0全局内存*/#define GLOBALMEM_MAJOR 0    /*预设的globalmem的主设备号*/static globalmem_major = GLOBALMEM_MAJOR;/*globalmem设备结构体*/struct globalmem_dev                                     {                                                          struct cdev cdev; /*cdev结构体*/                         unsigned char mem[GLOBALMEM_SIZE]; /*全局内存*/       struct semaphore sem; /*并发控制用的信号量*/      unsigned int current_len;//有效数据长度  wait_queue_head_t r_wait;//阻塞读用的等待队列头  wait_queue_head_t w_wait;//阻塞写用的等待队列头};struct globalmem_dev *globalmem_devp; /*设备结构体指针*//*文件打开函数*/int globalmem_open(struct inode *inode, struct file *filp){  /*将设备结构体指针赋值给文件私有数据指针*/  filp->private_data = globalmem_devp;  return 0;}/*文件释放函数*/int globalmem_release(struct inode *inode, struct file *filp){  return 0;}/* ioctl设备控制函数 */static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned  int cmd, unsigned long arg){  struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/  switch (cmd)  {    case MEM_CLEAR:      if (down_interruptible(&dev->sem))      {        return  - ERESTARTSYS;      }      memset(dev->mem, 0, GLOBALMEM_SIZE);      up(&dev->sem); //释放信号量      printk(KERN_INFO "globalmem is set to zero\n");      break;    default:      return  - EINVAL;  }  return 0;}/*读函数*/static ssize_t globalmem_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 globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/  DECLARE_WAITQUEUE(wait,current);//定义等待队列  /*分析和获取有效的写长度*/  if (p >= GLOBALMEM_SIZE)    return count ?  - ENXIO: 0;  if (count > GLOBALMEM_SIZE - p)    count = GLOBALMEM_SIZE - p;  if (down_interruptible(&dev->sem))  {    return  - ERESTARTSYS;  }  add_wait_queue(&dev->r_wait,&wait);//进入读等待队列头  //等待FIFO 非空  if(dev->current_len == 0)  {  if(filp->f_flags &O_NONBLOCK)  {  ret = -EAGAIN;goto out;  }__set_current_state(TASK_INTERRUPTIBLE);//改变进程状态为睡眠up($dev->sem);schedule();//跳读其他进程执行if(signal_pending(current))//如果是因为信号唤醒{ret = -ERESTARTSYS;goto out2;}down(&dev->sem);  }    /*内核空间->用户空间*/  if (copy_to_user(buf, (void*)(dev->mem + p), count))  {    ret =  - EFAULT;  }  else  {    *ppos += count;    ret = count;    printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);wake_up_interruptible(&dev->w_wait);//唤醒写队列  }  out:up(&dev->sem); //释放信号量  out2:remove_wait_queue(&dev->w_wait,&wait);//移除读等待队列头  set_current_state(TASK_RUNNING);  return ret;}/*写函数*/static ssize_t globalmem_write(struct file *filp, const char __user *buf,  size_t size, loff_t *ppos){  unsigned long p = *ppos;  unsigned int count = size;  int ret = 0;    struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/  DECLARE_WAITQUEUE(wait,curret);  /*分析和获取有效的写长度*/  if (p >= GLOBALMEM_SIZE)    return count ?  - ENXIO: 0;  if (count > GLOBALMEM_SIZE - p)    count = GLOBALMEM_SIZE - p;  if (down_interruptible(&dev->sem))//获得信号量  {    return  - ERESTARTSYS;  }  add_wait_queue(&dev->w_wait,&wait);  /*用户空间->内核空间*/  if(dev->current_len == GLOBALFIFO_SIZE)  {  if(filp->f_flags &O_NONBLOCK)  {  ret = -EAGAIN;goto out;  }__set_current_state(TASK_INTERRUPTIBLE);//改变进程状态为睡眠up($dev->sem);schedule();//跳读其他进程执行if(signal_pending(current))//如果是因为信号唤醒{ret = -ERESTARTSYS;goto out2;}down(&dev->sem);  }       if (copy_from_user(dev->mem + p, buf, count))    ret =  - EFAULT;  else  {     *ppos +=count;    ret = count;wake_up_interruptible(&dev->r_wait);    printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);  }  up(&dev->sem); //释放信号量  return ret;}/* seek文件定位函数 */static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig){  loff_t ret = 0;  switch (orig)  {    case 0:   /*相对文件开始位置偏移*/      if (offset < 0)      {        ret =  - EINVAL;        break;      }      if ((unsigned int)offset > GLOBALMEM_SIZE)      {        ret =  - EINVAL;        break;      }      filp->f_pos = (unsigned int)offset;      ret = filp->f_pos;      break;    case 1:   /*相对文件当前位置偏移*/      if ((filp->f_pos + offset) > GLOBALMEM_SIZE)      {        ret =  - EINVAL;        break;      }      if ((filp->f_pos + offset) < 0)      {        ret =  - EINVAL;        break;      }      filp->f_pos += offset;      ret = filp->f_pos;      break;    default:      ret =  - EINVAL;      break;  }  return ret;}/*文件操作结构体*/static const struct file_operations globalmem_fops ={  .owner = THIS_MODULE,  .llseek = globalmem_llseek,  .read = globalmem_read,  .write = globalmem_write,  .ioctl = globalmem_ioctl,  .open = globalmem_open,  .release = globalmem_release,};/*初始化并注册cdev*/static void globalmem_setup_cdev(struct globalmem_dev *dev, int index){  int err, devno = MKDEV(globalmem_major, index);  cdev_init(&dev->cdev, &globalmem_fops);  dev->cdev.owner = THIS_MODULE;  dev->cdev.ops = &globalmem_fops;  err = cdev_add(&dev->cdev, devno, 1);  if (err)    printk(KERN_NOTICE "Error %d adding LED%d", err, index);}/*设备驱动模块加载函数*/int globalmem_init(void){  int result;  dev_t devno = MKDEV(globalmem_major, 0);  /* 申请设备号*/  if (globalmem_major)    result = register_chrdev_region(devno, 1, "globalmem");  else  /* 动态申请设备号 */  {    result = alloc_chrdev_region(&devno, 0, 1, "globalmem");    globalmem_major = MAJOR(devno);  }    if (result < 0)    return result;      /* 动态申请设备结构体的内存*/  globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);  if (!globalmem_devp)    /*申请失败*/  {    result =  - ENOMEM;    goto fail_malloc;  }  memset(globalmem_devp, 0, sizeof(struct globalmem_dev));    globalmem_setup_cdev(globalmem_devp, 0);  init_MUTEX(&globalmem_devp->sem);   /*初始化信号量*/    init_waitqueue_head(&globalmem_devp->r_wait);  init_waitqueue_head(&globalmem_devp->w_wait);  return 0;  fail_malloc: unregister_chrdev_region(devno, 1);  return result;}/*模块卸载函数*/void globalmem_exit(void){  cdev_del(&globalmem_devp->cdev);   /*注销cdev*/  kfree(globalmem_devp);     /*释放设备结构体内存*/  unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); /*释放设备号*/}MODULE_AUTHOR("Song Baohua");MODULE_LICENSE("Dual BSD/GPL");module_param(globalmem_major, int, S_IRUGO);module_init(globalmem_init);module_exit(globalmem_exi

锁：

自旋锁：适用较短等待，CPU回在此空转

信号量：适用较长等待，进程间，又上下文切换，消费较大

Linux通常将中断分为上半部和下半部，上半部不可打断:应尽量减小耗时，完成中断等级，下半部完成全部处理，很多系统也采用这种形式。

timer

第十一章