Everything is a File
File = 实现了文件操作的 “Anything”
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 (*iopoll)(struct kiocb *kiocb, struct io_comp_batch *, uint flags);
int (*iterate_shared) (struct file *, struct dir_context *);
__poll_t (*poll) (struct file *, struct poll_table_struct *);
long (*unlocked_ioctl) (struct file *, uint, ul);
long (*compat_ioctl) (struct file *, uint, ul);
int (*mmap) (struct file *, struct vm_area_struct *);
ul mmap_supported_flags;
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 (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ul (*get_unmapped_area)(struct file *, ul, ul, ul, ul);
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, uint);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, uint);
void (*splice_eof)(struct file *file);
int (*setlease)(struct file *, int, struct file_lease **, void **);
long (*fallocate)(struct file *file, int mode, loff_t offset, loff_t len);
void (*show_fdinfo)(struct seq_file *m, struct file *f);
ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, uint);
loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in, struct file *file_out,
loff_t pos_out, loff_t len, uint remap_flags);
int (*fadvise)(struct file *, loff_t, loff_t, int);
int (*uring_cmd)(struct io_uring_cmd *ioucmd, uint issue_flags);
int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *,
uint poll_flags);
} __randomize_layout;