off_t file_read (struct file *, void *, off_t);
off_t file_read_at (struct file *, void *, off_t size, off_t start);
off_t file_write (struct file *, const void *, off_t);
off_t file_write_at (struct file *, const void *, off_t size, off_t start);
off_t file_read (struct file *, void *, off_t);
off_t file_read_at (struct file *, void *, off_t size, off_t start);
off_t file_write (struct file *, const void *, off_t);
off_t file_write_at (struct file *, const void *, off_t size, off_t start);