Linux简单的字符文件驱动.doc

Linux 简单的字符文件驱动字符设备是Linux 设备驱动中最简单的。struct cdev struct kobject *kobj; struct module *owner; /所属模块 struct file_operations *ops; struct list_head_list; dev_t dev; unsigned int count;1 设备编号：dev_t类型，高12位表示主设备号，低20位表示次设备号。一般同一类设备拥有同样的主设备，表示使用相同的驱动程序。次设备号用以区分不同的具体的设备，一般从0开始编号。系统中注册的设备在/pro/devices,内核文档中的devices.txt描述了Linux设备号的分配情况，由LANANA组织维护。下面的宏可以用主设备号和次设备号来生成设备号：MKDEV(int major,int minor)可以通过这两个宏来获取主设备号和从设备号：MAJOR(dev_t dev)MINOR(dev_t dev)通过下面的函数可以申请主设备号：int register_chrdev_region(dev_t from,unsigned count,const char *name);/from指定了已知起始设备int alloc_chrdev_region(dev_t *dev,unsigned baseminor,unsigned count,char *name);/向系统动态申请未被占用的设备号。void unregister_chrdev_region(dev_t form,unsigned count); /回收之前申请的设备号2 与字符设备cdev主要的函数：void cdev_init(struct cdev *,struct file_operations *); /建立cdev和file_operations之间的联系struct cdev *cdev_alloc();/分配新的cdevvoid cdev_put(struct cdev *);/回收cdev的空间void cdev_del(struct cdev *);/向系统注销设备int cdev_add(struct cdev *,dev_t ,unsigned int count); /向系统注册设备3 file_operations当VFS接收到对设备的读取等请求时，会调用到file_operations中对应的函数。在实现read和write时可能会需要使用下面的函数,进行用户空间和内核空间的数据交换。unsigned long copy_from_user(void *to,const void _user *from,unsigned long count);unsigned long copy_to_user(void _user *to,const void *from,unsigned long count);这两个函数返回未能拷贝的字节，如果成功，返回为0.如果数据类型是简单的数据，int long char等，可以使用更为简单的函数：比如要传递一个int，int val;get_user(val,(int *)arg);/用户空间到内核空间，arg为用户空间地址put_user(val,(int *)arg);/内核空间到用户空间_user宏表明后面指向的地址为用户空间。宏container_of(ptr,type,member)可以通过结构体的子项来定位整个结构体的指针。例如：struct Tint a;int b;struct T t =0;container_of(&t.a,int,a)就会返回指向T的指针来自于linux设备驱动开发详解的一个例子如下：#include #include #include #include #include #include #include #include #include #include #include #define MAX_SIZE (4096*2)#define MAX_DEV (2)/支持的子设备数struct mem_dev struct cdev dev; char memMAX_SIZE;struct mem_dev *g_mem_devp = NULL; static int mem_open(struct inode *inode,struct file *filp) /通过结构体成员找到结构体指针 struct mem_dev *devp = NULL; devp = container_of(inode-i_cdev,struct mem_dev,dev); filp-private_data = devp; printk(KERN_INFO sucess to openn); return 0;static ssize_t mem_read(struct file *filp,char _user *buf,size_t size,loff_t *ppos) int ret = 0; unsigned long pos = *ppos; struct mem_dev *dev = filp-private_data; if(pos MAX_SIZE) return size 0 ? -ENXIO : 0; if(size MAX_SIZE - pos) size = MAX_SIZE - pos; if(copy_to_user(buf,(void *)(dev-mem + pos),size) /if(copy_to_user(buf,(void *)(hello),6) ret = -EFAULT; else *ppos += size; /需要修改pos ret = size; printk(KERN_INFO read %d bytes at %dn,size,pos); if(ret 0) printk(KERN_INFO sucess to readn); return ret;static ssize_t mem_write(struct file *filp,char _user *buf,size_t size,loff_t *ppos) int ret = 0; unsigned long pos = *ppos; struct mem_dev *dev = filp-private_data; if(pos MAX_SIZE) return size 0 ? -ENXIO : 0; if(size MAX_SIZE - pos) size = MAX_SIZE - pos; if(copy_from_user(void *)(dev-mem + pos),buf,size) ret = -EFAULT; else *ppos += size; ret = size; printk(KERN_INFO write %d bytes at %dn,size,pos); if(ret 0) printk(KERN_INFO sucess to writen); return ret;static loff_t mem_llseek(struct file *filp, loff_t offset, int orig) loff_t ret = 0; switch(orig) case SEEK_SET: if(offset MAX_SIZE) ret = -EINVAL; break; filp-f_pos = offset; ret = filp-f_pos; break; case SEEK_CUR: if(offset + filp-f_pos f_pos MAX_SIZE) ret = -EINVAL; break; filp-f_pos += offset; ret = filp-f_pos; break; default: /inlucde SEEK_END ret = -EINVAL; break; return ret;static struct file_operations g_mem_fops = .owner = THIS_MODULE, .llseek = mem_llseek, .read = mem_read, .open = mem_open, .write = mem_write,;static int mem_init_cdev(struct mem_dev *devp,dev_t devno) cdev_init(&devp-dev,&g_mem_fops); devp-dev.ops = &g_mem_fops; devp-dev.owner = THIS_MODULE; devp-dev.dev = devno; return cdev_add(&devp-dev,devno,1);static int globalmem_init() int ret = 0; int i = 0; dev_t devno = 0; int major = 0; if(alloc_chrdev_region(&devno,0,MAX_DEV,global_mem) 0) printk(failed in alloc_chrdev_region); return -1; major = MAJOR(devno); if(g_mem_devp = kmalloc(MAX_DEV*sizeof(struct mem_dev),GFP_KERNEL) = NULL) ret = -ENOMEM; goto ERR; memset(g_mem_devp,0,MAX_DEV*sizeof(struct mem_dev); for(i = 0; i MAX_DEV; +i) ret = mem_init_cdev(&g_mem_devpi,MKDEV(major,i); prin