Linux高级字符设备驱动

#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 <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 "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 ;
} /*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{
return ;
} /*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 = ;
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 ;
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 */
{
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 */
/* 唤醒写进程 */
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 = ;
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 ;
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 : /* SEEK_SET */
newpos = offset;
break; case : /* SEEK_CUR */
newpos = filp->f_pos + offset;
break; case : /* SEEK_END */
newpos = MEMDEV_SIZE - + offset;
break; default: /* can't happen */
return -EINVAL;
}
if ((newpos<) || (newpos>MEMDEV_SIZE))
return -EINVAL; filp->f_pos = newpos;
return newpos; }
unsigned int mem_poll(struct file *filp, poll_table *wait)
{
struct mem_dev *dev = filp->private_data;
unsigned int mask = ; /*将等待队列添加到poll_table表中 */
poll_wait(filp, &dev->inq, wait); if (have_data) mask |= POLLIN | POLLRDNORM; /* readable */ return mask;
} /*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,
.poll = mem_poll,
}; /*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, ); /* 静态申请设备号*/
if (mem_major)
result = register_chrdev_region(devno, , "memdev");
else /* 动态分配设备号 */
{
result = alloc_chrdev_region(&devno, , , "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, ), 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, , sizeof(struct mem_dev)); /*为设备分配内存*/
for (i=; 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, , MEMDEV_SIZE); /*初始化等待队列*/
init_waitqueue_head(&(mem_devp[i].inq));
//init_waitqueue_head(&(mem_devp[i].outq));
} return ; fail_malloc:
unregister_chrdev_region(devno, ); 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, ), ); /*释放设备号*/
} MODULE_AUTHOR("David Xie");
MODULE_LICENSE("GPL"); module_init(memdev_init); module_exit(memdev_exit); ）测试程序app-read.c源码 #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; //声明描述符集合
int ret;
char Buf[]; /*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); //清空描述符集合
FD_SET(fd, &rds); //设置描述符集合 /*清除Buf*/
strcpy(Buf,"Buf is NULL!");
printf("Read BUF1: %s\n",Buf); ret = select(fd + , &rds, NULL, NULL, NULL);//调用select（）监控函数
if (ret < )
{
printf("select error!\n");
exit();
}
if (FD_ISSET(fd, &rds)) //测试fd1是否可读
read(fd, Buf, sizeof(Buf)); /*检测结果*/
printf("Read BUF2: %s\n",Buf); close(fd); return ;
}