标准文件IO之文件描述符

标准文件IO中打死的是一个句柄；句柄从0开始前三个分别为stdin ,stdout,stderr然后还有一个文件项中，有一个inode的文件点，根据这个文件点可以找到该文件在inode在磁盘中的位置 。

struct file {
	/*
	 * fu_list becomes invalid after file_free is called and queued via
	 * fu_rcuhead for RCU freeing
	 */
	union {
		struct list_head	fu_list;
		struct rcu_head 	fu_rcuhead;
	} f_u;
	struct path		f_path;
#define f_dentry	f_path.dentry
#define f_vfsmnt	f_path.mnt
	const struct file_operations	*f_op;
	spinlock_t		f_lock;  /* f_ep_links, f_flags, no IRQ */
#ifdef CONFIG_SMP
	int			f_sb_list_cpu;
#endif
	atomic_long_t		f_count;
	unsigned int 		f_flags;
	fmode_t			f_mode;
	loff_t			f_pos;
	struct fown_struct	f_owner;
	const struct cred	*f_cred;
	struct file_ra_state	f_ra;

	u64			f_version;
#ifdef CONFIG_SECURITY
	void			*f_security;
#endif
	/* 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;
#endif /* #ifdef CONFIG_EPOLL */
	struct address_space	*f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
	unsigned long f_mnt_write_state;
#endif
};

`struct path {
	struct vfsmount *mnt;
	struct dentry *dentry;
};``
在struct file结构体中有