globalmem虚拟字符设备驱动--字符驱动讲解（2）

1、什么是globalmem虚拟设备？？

（1）、globalmem字符设备驱动中，分配一片内存大小为GLOBALMEM_SIZE(4K)的空间

（2）、提供对该片内存的读写、控制和定位函数

（3）、用户进程能够通过linux系统调用访问这篇内存

#include <linux/module.h>#include <linux/init.h>#include <linux/types.h>#include <linux/fs.h>#include <linux/errno.h>#include <linux/mm.h>#include <linux/sched.h>#include <linux/cdev.h>#include <asm/io.h>#include <asm/system.h>#include <asm/uaccess.h>#define GLOBALMEM_SIZE 0X1000 /*全局内存最大4KB*/#define MEM_CLEAR 0x1 /*清零全局内存*/#define GLOBALMEM_MAJOR 254static globalmem_major = GLOBALMEM_MAJOR;/*预设的globalmem的主设备号*//*globalmem的设备结构体：包含了对应于globalmem字符设备的cdev 和 使用内存mem[GLOBALMEM_SIZE]*/struct globalmem_dev{ struct cdev cdev;  //cdev结构体 unsigned char mem[GLOBALMEM_SIZE);  //全局内存};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){ filp->private_data = globalmem_devp; //将设备结构体指针赋值给文件私有数据指针 return 0}/*文件释放函数*/int globalmem_release(struct inode *inode,struct file *filp){ return 0;}/*设备控制函数：ioctl()函数接受的MEM_CLEAR命令，这个命令将全局内存的有效数据长度清零，对于设备不支持的命令，ioctl()函数应该返回-EINVAL*/static int globalmen_ioctl(struct inode *inodep,struct file *filp,unsigned int cmd,unsigned long arg){ struct globalmen_dev *dev = filp->private_data; //获得设备结构体指针 switch(cmd) {  case  MEE_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：读写函数主要是让设备结构体的mem[]数组与用户空间交互数据，并随着访问字节数变更返回用户的文件读写偏移位置*/static ssizez_t globalmem_read(struct file *filp,char __user *buf,size_t size,loff_t *opps){ 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  if(p >= GLOBALMEM_SIZE)  //分析和获取有效的写长度 {  return count ? -ENXIO:0; } if(count > GLOBAL_SIZE - P) {  count = GLOBALMEN_SIZE - P; }  if(copy_to_user(buf,(void *)(dev->mem+p),count))  //内核空间->用户空间 {  ret = -ENAU;T; } else {  *oppos += count;  ret = count;  printk(KERN_INFO"read %d bytes(s) from %d\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;  struct globalmem_dev *dev = filp->private_data;  if(p >= CLOBALMEM_SIZE)  //分析和获取有效的写长度 {  return count? -ENXIO:0; }  if(count > GLOBALMEN_SIZE - P) {  count = CLOBALMEN_SIZE - P; }  if(copy_from_user(dev->mem + p,buf,count)) // 用户空间->内核空间 {  ret = -ENAULT; } 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：seek()函数对文件定位的起始地址可以是文件开头(SEEK_SET,0)、当前位置(SEEK_CUR,1)、文件尾(SEEK_END,2)*/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_ops = (unsigned int)offset;   ret = filp->f_pos;   break;     case 1:   //相对文件当前位置偏移   if((filp->f_ops + offset) > GLOBALMEMSIZE)   {    ret = -EINVAL;    break;   }   if((filp->f_ops + offset)<0)   {    ret = -ENVAL;    break;   }   filp->f_ops +=offset;   ret = filp->f_ops;   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(globalmen_major,index); cdev_init(&dev->cdev,&globalmem_fops); dev->cdev.owner = THIS_MOUDEL; dev->cdev.ops = &golbalmem_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*/static int __init globalmem_init(void){ int result; dev_t devno = MKDEV(globalmem_major,0);  if(globalmem_major) //申请设备号 {  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 < 0) {  return result; }  globalmem_devp = kmalloc(sizeof(struct globalmem_dev),GFP_KERNEL); //申请设备结构体的内存 if(!globalmem_devp) {  result = -ENOMEM;  goto fail_malloc; }  memset(globalmem_devp,0,sizeof(struct globalmem_dev)); globalmem_setup_cdev(globalmem_devp,0); return 0;  fail_malloc:unregister_chrdev_region(devno,1); return result;}/*模块卸载函数*/void __eixt 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("NOODLE");MODULE_LICENSE("GPL");mdule_param(globalmem_major,int,S_IRUGO);module_init(globalmem_init);module_exit(globalmem_exit);