android底层驱动学习之从应用程序如何到底层driver的调用 linux驱动

1.首先来看下struct file_operations 的定义：
【android底层驱动学习之从应用程序如何到底层driver的调用】

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); };

在这里面有很多函数，比如 open 、read、write函数，他们通过以下方式初始化：

static const struct file_operations fts_proc_fops = { .owner = THIS_MODULE, .open = fts_debug_open, .write = fts_debug_write,};

那问题就来了，fts_debug_open是如何实现调用的呢？ /************************************
来看一个在应用程序中的调用实例：
fd=open("/dev/hello",O_RDWR)

以上是通过系统调用open函数打开/dev/hello这个设备文件，此设备节点对应有一个设备号
打开/dev/hello通过主次设备号找到相对应的字符设备，
struct cdev {
struct kobject kobj;
struct module *owner;
const struct file_operations *ops;
struct list_head list;
dev_t dev;
unsigned int count;
};

cdev里面又包含了file_operations结构体，含有对设备的各种操作，打开时即调用里面的.open 函数指针指向的open函数。