vfs_iter_read
ret = vfs_iter_read(fd, &iter, &pos, 0);
return vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
ret = vfs_iter_read(cfi->cfi_container, to, &iocb->ki_pos, 0);
EXPORT_SYMBOL(vfs_iter_read);
ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,