我们在学习 C 语言的时候,知道每个应用程序的入口函数,即第一个被执行的函数是 main函数,那么,我们自己的驱动程序,哪个函数是入口函数呢?
在写驱动程序的时候,如果函数的名字可以任意取,常常为 xxxx_init(),当实现好这个 xxxx_init()函数以后,内核其实并不知道这个就是我们驱动的入口函数,因此我们要想办法告诉内核,我们的入口函数是哪个?我们通过 module_init()函数来告诉内核,具体如下。
module_init(RT5350_drv_init);
通过上面的修饰以后, RT5350_drv_init()这个函数就变成了我们的驱动程序的入口函数了。当然,有入口函数,自然还需要一个出口函数,我们通过 module_exit()函数来告诉内核,具体如下。
module_exit(RT5350_drv_exit);
从上一章中,我们知道,应用程序是通过 open、read、write ...函数来和我们的驱动程序进行交互的,那么我们的驱动程序是怎么给应用程序提供这些接口的呢?我们在写驱动程序的时候,我们首先需要定义出一个 file_operations 结构体,该结构体便是驱动和应用程序交互的接口。具体定义如下。
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 (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long,loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long,loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, loff_t, loff_t, 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 (*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);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t,
unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};