file_operations -- file -- inode

http://blog.chinaunix.net/space.php?uid=11412571&do=blog&cuid=343846

驱动中有几个重要的数据结构:
        file_operations,file,inode
中定义了这三个结构.
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 *);
        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 (*dir_notify)(struct file *filp, unsigned long arg);
}
   file_operations结构定义了一组函数指针,每一个打开的文件(用struct file表示)和他自己的一组函数(包含在一个叫f_op的域中,它指向一个struct file_operations结构)相联系.这些操作都是来实现系统调用的,所以才被命名为open,read,等等.对于那些不需要的功能(比如你的设备不需要write功能,即不需要向设备写数据),可以给write指针付NULL.

struct file {
        struct list_head        f_list;
        struct dentry           *f_dentry;
        struct vfsmount         *f_vfsmnt;
        struct file_operations *f_op;
        atomic_t                f_count;
        unsigned int            f_flags;
        mode_t                  f_mode;
        int                     f_error;
        loff_t                  f_pos;
        struct fown_struct      f_owner;
        unsigned int            f_uid, f_gid;
        struct file_ra_state    f_ra;

unsigned long f_version;
void *f_security;

/* needed for tty driver, and maybe others */
void *private_data;

#ifdef CONFIG_EPOLL
        /* Used by fs/eventpoll.c to link all the hooks to this file */
        struct list_head        f_ep_links;
        spinlock_t              f_ep_lock;
#endif /* #ifdef CONFIG_EPOLL */
        struct address_space    *f_mapping;
};
   每个打开的文件对应一个struct file.它在被打开时由内核创建,并传给它所有可以操作该文件的函数,到文件被关闭时才被删除.

The inode Structure.
   Inode结构是用来在内核内部表示文件的.同一个文件可以被打开好多次,所以可以对应很多struct file,但是只对应一个struct inode.该结构里面包含了很多信息,但是,驱动开发者只关心里面两个重要的域:
        dev_t i_rdev;//含有真正的设备号
        struct cdev *i_cdev;//struct cdev是内核内部表示字符设备的结构.
   struct file_operations是struct file的一个域，我们在使用系统调用open()打开一个设备节点struct inode时，我们会得到一个文件struct file,同时返回一个文件描述符，该文件描述符是一个整数，我们称之为句柄，通过访问句柄我们能够访问设备文件struct file,描述符是一个有着特殊含义的整数，特定位都有一定的意义或属性。

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