Linux字符设备驱动

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Linux字符设备驱动

1. 字符设备驱动的组成

在Linux系统中，字符设备驱动由如下几部分组成：设备相关结构体、字符设备驱动模块的加载与卸载函数、字符设备驱动中file_operations的成员函数。

1）设备相关结构体

在Linux驱动程序中，工程师一般习惯为相关设备建立一个结构体，其中包含cdev、私有数据、信号量等信息，如下：

<pre name="code" class="cpp">/*驱动结构体*/struct xxx_dev_t{       struct cdev cdev;       ......}xxx_dev;

2) 字符设备驱动模块的加载与卸载函数

加载函数的功能为：实现cdev结构体的注册和设备号的申请、设备的初始化等；卸载函数功能：相应结构体的注销和设备号的注销、资源的释放等；

加载

/************************************************************************   Function Name:  globalmem_init*   Paramter:       type name [IN]: void*   Function Descrition:*                   Module init*   Return: 0*   Error:*   Author: Vinvian 2014/11/11***********************************************************************/static int globalmem_init(void){    printk(KERN_INFO " Globlamem Driver for init!\n");    /*init cdev*/    ...    /*register dev no*/    ...    return 0;}

卸载

/************************************************************************   Function Name:  globalmem_exit*   Paramter:       type name [IN]: void*   Function Descrition:*                   Module exit*   Return: void*   Error:*   Author: Vinvian 2014/11/11***********************************************************************/static void globalmem_exit(void){    printk(KERN_INFO " Globlamem Driver for exit!\n");        /*release dev no*/    ...    /*del cdev*/    ...   }

3）file_operations结构体

该结构体是字符设备驱动的主体内容，是Linux驱动与应用程序及与底层处理的桥梁。

4）字符设备驱动程序的结构

字符设备驱动程序的结构，如下图所示。

2. globalmem虚拟设备驱动实例

1) 头文件及宏定义

#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>/*struct mem*/#define GLOBALMEM_SIZE0x1000/*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*/

2）结构体定义

static globalmem_major = GLOBALMEM_MAJOR;/*globalmem struct*/struct globalmem_dev{    struct cdev cdev;   /*cdev struct*/    unsigned char mem[GLOBALMEM_SIZE];  /*全局内存，私有数据*/};/*dev struct piont*/struct globalmem_dev *globalmem_devp = NULL;

3）函数主体

/*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:      memset(dev->mem, 0, GLOBALMEM_SIZE);      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;  /*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 %ld\n", count, p);  }  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;  /*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);  }  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,};/************************************************************************   Function Name:  globalmem_setup_cdev*   Paramter:*           struct globalmem_dev *dev [INOUT];*           int index   [IN];*   Function Descrition:*                   cdev init and register.*   Return: void*   Author: Vinvian 2014/11/11***********************************************************************/static void globalmem_setup_cdev(struct globalmem_dev *dev, int index){  int err = 0;  int devno = MKDEV(globalmem_major, index);  cdev_init(&dev->cdev, &globalmem_fops);       //dev init  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);}/************************************************************************   Function Name:  globalmem_init*   Paramter:       type name [IN]: void*   Function Descrition:*                   Module init*   Return: 0*   Error:*   Author: Vinvian 2014/11/11***********************************************************************/static int globalmem_init(void){   printk(KERN_INFO " Globlamem Driver for init!\n");    int result;    dev_t devno = MKDEV(globalmem_major, 0); //Create det_t with major and minor devNo    /*Regsiter devNo*/    if (globalmem_major)    //has major no        result = register_chrdev_region(devno, 1, "globalmem");    else                    //no major no    {        result = alloc_chrdev_region(&devno, 0, 1, "globalmem");        globalmem_major = MAJOR(devno);    }    if (result < 0)        return result;    /*malloc dev struct mem*/    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));    /*init cdev*/    globalmem_setup_cdev(globalmem_devp, 0);    return 0;    fail_malloc: unregister_chrdev_region(devno, 1);    return result;}/************************************************************************   Function Name:  globalmem_exit*   Paramter:       type name [IN]: void*   Function Descrition:*                   Module exit*   Return: void*   Error:*   Author: Vinvian 2014/11/11***********************************************************************/void globalmem_exit(void){    /*release cdev*/    cdev_del(&globalmem_devp->cdev);    /*release struct dev mem*/    kfree(globalmem_devp);    /*release devNo*/    unregister_chrdev_region(MKDEV(globalmem_major, 0), 1);}

4）

module_init(globalmem_init);module_exit(globalmem_exit);module_param(globalmem_major, int, S_IRUGO);MODULE_LICENSE("Dual BSD/GPL");MODULE_AUTHOR("Vinvian");MODULE_DESCRIPTION("A globalmem driver Module");MODULE_ALIAS("A globalmem driver");

3. 扩展学习

1）cdev_init();

2) cdev_add();

3) 宏MKDEV();

4. 参考文献

1）Linux设备驱动开发详解宋宝华著

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