3、含并发控制的globalmem驱动

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主要是用信号量（或锁）对设备进行并发控制，使得同一时刻只有一进程能写（读）)该设备
/*======================================================================
    A globalmem driver as an example of char device drivers  
    This example is to introduce how to use locks to avoid race conditions
   
    The initial developer of the original code is Baohua Song
    . All Rights Reserved.
======================================================================*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#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 254    /*预设的globalmem的主设备号*/
static int 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*/   
};
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*/
  /*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;
  }
  /*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);
  }
  up(&dev->sem); //释放信号量
  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*/
  /*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;
  }
  /*用户空间->内核空间*/
  if (copy_from_user(dev->mem + p, buf, count))
    ret =  - EFAULT;
  else
  {
    *ppos += count;
    ret = count;
    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  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) 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 sem);   /*初始化信号量*/  
  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_exit);


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