file_operations
结构体file_operations在头文件 linux/fs.h中定义,用来存储驱动内核模块提供的对设备进行各种操作的函数的指针。该结构体的每个域都对应着驱动内核模块用来处理某个被请求的 事务的函数的地址。
举个例子,每个字符设备需要定义一个用来读取设备数据的函数。结构体 file_operations中存储着内核模块中执行这项操作的函数的地址。一下是该结构体 在内核2.6.5中看起来的样子:
struct file_operations {
struct module *owner;
loff_t(*llseek) (struct file *, loff_t, int);
ssize_t(*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t(*aio_read) (struct kiocb *, char __user *, size_t, loff_t);
ssize_t(*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t(*aio_write) (struct kiocb *, const char __user *, size_t, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, struct dentry *, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t(*readv) (struct file *, const struct iovec *, unsigned long, loff_t *);
ssize_t(*writev) (struct file *, const struct iovec *, unsigned long, loff_t *);
ssize_t(*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void __user *);
ssize_t(*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area) (struct file *, unsigned long,
unsigned long, unsigned long,
unsigned long);
};
register_chrdev
首先我们在注册函数里面调用了register_chrdev(MEM_MAJOR,"mem",&memory_fops),向内核注册了一个字符设备。第一个参数是主设备号,0代表动态分配,这里的MEM_MAJOR是1。第二个参数是设备的名字,第三个参数是文件操作指针。每个设备文件对应有两个设备号:一个是主设备号,标识该设备的种类,也标识了该设备所使用的驱动程序;另一个是次设备号,标识使用同一设备驱动程序的不同硬件设备。设备文件的主设备号必须与设备驱动程序在登录该设备时申请的主设备号一致,否则用户进程将无法访问到设备驱动程序。
c表示字符设备
d表示目录
-表示常规设备
加载卸载
module_init(函数名);
module_exit(函数名);
class_device
class_device_create
class
class_create
module_license