文件（file）定义于include/linux/fs.h。

文件对象代表已经被进程打开的文件，主要是建立进程和文件之间的对应关系。它由open系统调用创建，由close系统调用销毁，且仅当进程访问文 件期间存在于内存中。同一个物理文件可能存在多个对应的文件对象，但对应的索引节点对象确是唯一的。当多个进程同时打开和操作同一个文件，同一个文件可能 存在多个对应的文件对象，但是它对应的索引节点和目录项却是唯一的。

struct file {
    union {
        struct llist_node       fu_llist;
        struct rcu_head         fu_rcuhead;
    } f_u;
    struct path             f_path;
    struct inode            *f_inode;       /* cached value */
    const struct file_operations    *f_op;
    /*
     * Protects f_ep_links, f_flags.
     * Must not be taken from IRQ context.
     */
    spinlock_t              f_lock;
    atomic_long_t           f_count;
    unsigned int            f_flags;
    fmode_t                 f_mode;
    struct mutex            f_pos_lock;
    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;
    struct list_head        f_tfile_llink;
#endif /* #ifdef CONFIG_EPOLL */
    struct address_space    *f_mapping;
};

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 (*read_iter) (struct kiocb *, struct iov_iter *);
    ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
    int (*iterate) (struct file *, struct dir_context *);
    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 (*mremap)(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 **, void **);
    long (*fallocate)(struct file *file, int mode, loff_t offset,
                      loff_t len);
    void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMU
    unsigned (*mmap_capabilities)(struct file *);
#endif
};