/**
*此實例涉及到線程的掛起與競態,字符IO的堵塞與非堵塞
*/
struct scull_pipe {
wait_queue_head_t inp, outp;
char *buffer, *end;
char *rp, wp;
//int buffersize;
int nreaders, nwriters;
struct fasync_struct *async_queue;
struct semaphore sem;
struct cdev cdev;
};
/**
* container_of - cast a member of a structure out to the containing structure
* @ptr: the pointer to the member.
* @type: the type of the container struct this is embedded in.
* @member: the name of the member within the struct.
* /inlcude/linux/kernel.h
*
*/
/*#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
*/
static ssize_t scull_p_read (struct file *filp, char __user *buffer, size_t count, loff_t *f_pos)
{
/*得到指向結構體scull_pipe的指針*/
/*
(void *private_data)private_data指針是file結構體中的成員之一,
它是跨系統挑用是保存狀態信息的非常有用的資源,這裏我們
在open階段使用container_of函數得到指向結構體scull_pipe的指針並將private_data指向它
記住要在release方法中釋放其內存
*/
struct scull_pipe *dev = filp->private_data;
/*使用信號量限制在同一時刻只有一個線程執行*/
/*若被中斷則返回非零值,若無法撤銷任何用戶可見的修改return - EINTR*/
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
while (dev->rp == dev->wp)
{
up_interruptible(&dev->sem);
/*判斷用戶是否設置了非堵塞IO*/
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
/*將線程掛起*/
if (wait_event_interruptible(&dev->inp, dev->rp != dev->wp))
return -ERESTARTSYS;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
}
/*min函數在Linux內核/include/linux/kernel.h中*/
if (dev->wp > dev->rp)
count = min(count, (size_t) (dev->wp - dev->rp));
else
count = min(count, (size_t) (dev->end - dev->rp));
if (copy_to_user(buffer, dev->rp, count))
{
up_interruptible(&dev->sem);
return -EFAULT;
}
dev->rp += count;
if (dev->rp == dev->end)
dev->rp = dev->buffer
up_interruptible(&dev->sem);
wake_up_interruptible(&dev->outp);
return count;
}
/*個人仿照上方寫的管道寫操作代碼*/
static ssize_t scull_p_write (struct file *filp, const char __user *buffer, size_t count, loff_t *f_pos)
{
struct scull_pipe *dev = filp->private_data;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
/*判斷條件有所不同*/
while (strlen(dev->buffer) && dev->rp == dev->wp)
{
up_interruptible(&dev->sem);
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
if (wait_event_interruptible(&dev->outp))
return -ERESTARTSYS;
down_interruptible(&dev->sem);
}
if (dev->wp > dev->rp)
count = min(count, (size_t) (dev->end - dev->wp));
else
count = min(count, (size_t) (dev->rp - dev->wp - 1));
if (copy_form_user(dev->wp, buffer, count))
{
up_interruptible(&dev->sem);
return -EFAULT;
}
dev->wp += count;
if (dev->wp == dev->end)
dev->wp = dev->buffer;
up_interruptible(&dev->sem);
wake_up_interruptible(&dev->inp);
return count;
}
高級字符驅動之堵塞與非堵塞IO
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