Linux高级字符设备之Poll操作

在用户程序中，select()和poll()也是与设备阻塞与非阻塞访问息息相关的，使用非阻塞I/O的应用程序通常会使用select和poll系统调用查询是否可对设备进行无阻塞的访问。select系统调用最终会引发设备驱动中的poll函数被执行。

一、select()系统调用：

用于多路监控，当没有一个文件满足要求时，select将阻塞调用进程。

1.select()原型：
int select(int maxfdp,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,const struct timeval *timeout);

/*

*@maxfd : 需要检查的文件描述符个数，数值应该比是三组fd_set中最大数更大(即一般取所有文件描述符的最大值加1)，而不是实际文件描述符的总数。

*@readfds: 用来检查可读性的一组文件描述符。

*@writesfds: 用来检查可写性的一组文件描述符。

*@exceptsfds:用来检查意外状态的文件描述符。(注：错误并不是意外状态)
*@timeout:NULL指针代表无限等待，否则是指向timeval结构的指针，代表最长等待时间。(如果其中tv_sec和tv_usec都等于0, 则文件描述符的状态不被影响，但函数并不挂起)

返回值：

（1）正常情况下返回满足要求的文件描述符个数；

（2）经过了timeout等待后仍无文件满足要求，返回0；

（3）如果select被某个信号中断，将返回-1并设置errno为EINTR；

（4）若出错，返回-1并设置相应的errno；

2.select的使用方法：

（1）将要监控的文件添加到文件描述符集；

（2）调用select开始监控；

（3）判断文件是否发生变化；

 

3.系统提供四个宏对描述符集进行操作：

void FD_SET(int fd, fd_set *fdset); //将文件描述符fd添加到文件描述符集fdset中；
void FD_CLR(int fd, fd_set *fdset); //从文件描述符集fdset中清除文件描述符fd；
void FD_ISSET(int fd, fd_set *fdset); //在调用select后使用FD_ISSET来检测文件描述符集中的文件fd发生了变化
void FD_ZERO(fd_set *fdset);//清空文件描述符集

二、Poll方法：

1.poll函数原型：

unsigned int(*poll)(struct file *filp, struct poll_table *wait);
//第一个参数为file结构体指针，第二个参数为轮询表指针。

这个函数应该进行以下两项工作:

（1）对可能引起设备文件状态变化的等待队列调用poll_wait()函数，将对应等待队列添加到poll_table中； 

（2）返回表示是否能对设备进行无阻塞可读或可写访问的掩码；

　　位掩码：POLLRDNORM， POLLIN，POLLOUT，POLLWRNORM

　　设备可读，通常返回：(POLLIN | POLLRDNORM)

　　设备可写，通常返回：(POLLOUT | POLLWRNORM)

三、调用过程：

Linux下select调用的过程:

1、用户层应用程序调用select(),底层调用poll())

2、核心层调用sys_select() ------> do_select()

　　最终调用文件描述符fd对应的struct file类型变量的struct file_operations *f_op的p
4000
oll函数。

　　poll指向的函数返回当前可否读写的信息。

　　1)如果当前可读写，返回读写信息。

　　2)如果当前不可读写，则阻塞进程，并等待驱动程序唤醒，重新调用poll函数，或超时返回。

3、驱动需要实现poll函数。

当驱动发现有数据可以读写时，通知核心层，核心层重新调用poll指向的函数查询信息。

poll_wait(filp,&wait_q,wait) // 此处将当前进程加入到等待队列中，但并不阻塞

　　在中断中使用wake_up_interruptible(&wait_q)唤醒等待队列。

 

四、实例分析：

1.memdev.h<div class="cnblogs_code" style="border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; font-family: 'Courier New' !important; background-color: rgb(245, 245, 245);"><img id="code_img_opened_38253450-1c6c-400f-a62a-602c08555f78" class="code_img_opened" src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif" alt="" style="border: 0px; vertical-align: middle; padding-right: 5px;" /><div id="cnblogs_code_open_38253450-1c6c-400f-a62a-602c08555f78" class="cnblogs_code_hide"><div class="cnblogs_code_toolbar" style="margin-top: 5px;"><span class="cnblogs_code_copy" style="padding-right: 5px; line-height: 1.5 !important;"><a target=_blank title="复制代码" style="color: rgb(119, 0, 0); font-size: 13px; border: none !important;"><img src="http://common.cnblogs.com/images/copycode.gif" alt="复制代码" style="border: none !important;" /></a></span></div><pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: 'Courier New' !important;">#ifndef _MEMDEV_H_
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#define</span> _MEMDEV_H_

#ifndef MEMDEV_MAJOR
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#define</span> MEMDEV_MAJOR 0 /*预设的mem的主设备号*/
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#endif</span>

#ifndef MEMDEV_NR_DEVS
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#define</span> MEMDEV_NR_DEVS 2 /*设备数*/
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#endif</span>

#ifndef MEMDEV_SIZE
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#define</span> MEMDEV_SIZE 4096
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">#endif</span>

/*mem设备描述结构体*/
struct mem_dev
{
char *data;
unsigned long size;
wait_queue_head_t inq;
};

#endif /* _MEMDEV_H_ */

<span style="line-height: 23.3999996185303px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; background-color: rgb(238, 238, 221);">2.</span><span style="line-height: 23.3999996185303px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; background-color: rgb(238, 238, 221);">memdev.c</span>

<span style="line-height: 23.3999996185303px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; background-color: rgb(238, 238, 221);">
</span><div class="cnblogs_code_toolbar" style="margin-top: 5px; font-family: 'Courier New'; line-height: 21.6000003814697px; background-color: rgb(245, 245, 245);"><span class="cnblogs_code_copy" style="padding-right: 5px; line-height: 1.5 !important;"><a target=_blank title="复制代码" style="color: rgb(119, 0, 0); font-size: 13px; border: none !important;"><img src="http://common.cnblogs.com/images/copycode.gif" alt="复制代码" style="border: none !important;" /></a></span></div><pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; line-height: 21.6000003814697px; font-family: 'Courier New' !important;">#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 <asm/system.h>
#include <asm/uaccess.h>

#include <linux/poll.h>
#include <span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">memdev.h</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> mem_major = MEMDEV_MAJOR;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">bool</span> have_data = <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">false</span>; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">表明设备有足够数据可供读</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

module_param(mem_major, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span>, S_IRUGO);

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev *mem_devp; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">设备结构体指针</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> cdev cdev;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">文件打开函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> mem_open(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> inode *inode, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp)
{
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev *dev;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">获取次设备号</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> num = MINOR(inode->i_rdev);

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (num >= MEMDEV_NR_DEVS)
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> -ENODEV;
dev = &mem_devp[num];

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">将设备描述结构指针赋值给文件私有数据指针</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
filp->private_data = dev;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">文件释放函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> mem_release(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> inode *inode, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp)
{
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">读函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> ssize_t mem_read(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">char</span> __user *buf, size_t size, loff_t *ppos)
{
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">long</span> p =  *ppos;
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> count = size;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> ret = <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev *dev = filp->private_data; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">获得设备结构体指针</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">判断读位置是否有效</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (p >= MEMDEV_SIZE)
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">while</span> (!have_data) <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 没有数据可读，考虑为什么不用if，而用while </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
{
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (filp->f_flags & O_NONBLOCK)
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> -EAGAIN;

wait_event_interruptible(dev->inq,have_data);
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">读数据到用户空间</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (copy_to_user(buf, (<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">void</span>*)(dev->data + p), count))
{
ret =  - EFAULT;
}
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">else</span>
{
*ppos += count;
ret = count;

printk(KERN_INFO <span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">read %d bytes(s) from %d\n</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>, count, p);
}

have_data = <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">false</span>; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 表明不再有数据可读 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0,
102be
128, 0); line-height: 1.5 !important;"> 唤醒写进程 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> ret;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">写函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> ssize_t mem_write(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">const</span> <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">char</span> __user *buf, size_t size, loff_t *ppos)
{
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">long</span> p =  *ppos;
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> count = size;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> ret = <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev *dev = filp->private_data; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">获得设备结构体指针</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">分析和获取有效的写长度</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (p >= MEMDEV_SIZE)
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (count > MEMDEV_SIZE - p)
count = MEMDEV_SIZE - p;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">从用户空间写入数据</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (copy_from_user(dev->data + p, buf, count))
ret =  - EFAULT;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">else</span>
{
*ppos += count;
ret = count;

printk(KERN_INFO <span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">written %d bytes(s) from %d\n</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>, count, p);
}

have_data = <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">true</span>; <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 有新的数据可读 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 唤醒读进程 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
wake_up(&(dev->inq));

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> ret;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> seek文件定位函数 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> loff_t mem_llseek(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp, loff_t offset, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> whence)
{
loff_t newpos;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">switch</span>(whence) {
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">case</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>: <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> SEEK_SET </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
newpos = offset;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">break</span>;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">case</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">1</span>: <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> SEEK_CUR </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
newpos = filp->f_pos + offset;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">break</span>;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">case</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">2</span>: <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> SEEK_END </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
newpos = MEMDEV_SIZE -<span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">1</span> + offset;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">break</span>;

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">default</span>: <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> can't happen </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> -EINVAL;
}
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> ((newpos<<span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>) || (newpos>MEMDEV_SIZE))
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> -EINVAL;

filp->f_pos = newpos;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> newpos;

}
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> mem_poll(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> file *filp, poll_table *wait)
{
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev  *dev = filp->private_data;
unsigned <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> mask = <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">将等待队列添加到poll_table </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
poll_wait(filp, &dev->inq,  wait);

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (have_data)         mask |= POLLIN | POLLRDNORM;  <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> readable </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> mask;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">文件操作结构体</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">const</span> <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> 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,
};

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">设备驱动模块加载函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> memdev_init(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">void</span>)
{
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> result;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">int</span> i;

dev_t devno = MKDEV(mem_major, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>);

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 静态申请设备号</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (mem_major)
result = register_chrdev_region(devno, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">2</span>, <span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">memdev</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>);
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">else</span>  <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 动态分配设备号 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
{
result = alloc_chrdev_region(&devno, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">2</span>, <span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">memdev</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>);
mem_major = MAJOR(devno);
}

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (result < <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>)
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> result;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">初始化cdev结构</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
cdev_init(&cdev, &mem_fops);
cdev.owner = THIS_MODULE;
cdev.ops = &mem_fops;

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 注册字符设备 </span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
cdev_add(&cdev, MKDEV(mem_major, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>), MEMDEV_NR_DEVS);

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;"> 为设备描述结构分配内存</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
mem_devp = kmalloc(MEMDEV_NR_DEVS * <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">sizeof</span>(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev), GFP_KERNEL);
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">if</span> (!mem_devp)    <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">申请失败</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
{
result =  - ENOMEM;
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">goto</span> fail_malloc;
}
memset(mem_devp, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>, <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">sizeof</span>(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">struct</span> mem_dev));

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">为设备分配内存</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">for</span> (i=<span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>; 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, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>, MEMDEV_SIZE);

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">初始化等待队列</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
init_waitqueue_head(&(mem_devp[i].inq));
<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">//</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">init_waitqueue_head(&(mem_devp[i].outq));</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">
</span>  }

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>;

fail_malloc:
unregister_chrdev_region(devno, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">1</span>);

<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">return</span> result;
}

<span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">模块卸载函数</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">static</span> <span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">void</span> memdev_exit(<span style="color: rgb(0, 0, 255); line-height: 1.5 !important;">void</span>)
{
cdev_del(&cdev);   <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">注销设备</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
kfree(mem_devp);     <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">释放设备结构体内存</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
unregister_chrdev_region(MKDEV(mem_major, <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">0</span>), <span style="color: rgb(128, 0, 128); line-height: 1.5 !important;">2</span>); <span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">/*</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">释放设备号</span><span style="color: rgb(0, 128, 0); line-height: 1.5 !important;">*/</span>
}

MODULE_AUTHOR(<span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">David Xie</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>);
MODULE_LICENSE(<span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">GPL</span><span style="color: rgb(128, 0, 0); line-height: 1.5 !important;">"</span>);

module_init(memdev_init);
module_exit(memdev_exit);

3.app-write.c

#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 memdev 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;

}

4.app-read.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>

int main()
{
int fd;
fd_set rds;
int ret;
char Buf[128];

/*初始化Buf*/
strcpy(Buf,"memdev is char dev!");
printf("BUF: %s\n",Buf);

/*打开设备文件*/
fd = open("/dev/memdev0",O_RDWR);

FD_ZERO(&rds);
FD_SET(fd, &rds);

/*清除Buf*/
strcpy(Buf,"Buf is NULL!");
printf("Read BUF1: %s\n",Buf);

ret = select(fd + 1, &rds, NULL, NULL, NULL);
if (ret < 0)
{
printf("select error!\n");
exit(1);
}
if (FD_ISSET(fd, &rds))
read(fd, Buf, sizeof(Buf));

/*检测结果*/
printf("Read BUF2: %s\n",Buf);

close(fd);

return 0;
}

void FD_SET(int fd, fd_set *fdset); //将文件描述符fd添加到文件描述符集fdset中；
void FD_CLR(int fd, fd_set *fdset); //从文件描述符集fdset中清除文件描述符fd；
void FD_ISSET(int fd, fd_set *fdset); //在调用select后使用FD_ISSET来检测文件描述符集中的文件fd发生了变化
void FD_ZERO(fd_set *fdset);//清空文件描述符集