rem: user_write(int fd, const void *buffer, off_t pos, size_t length)
add: user_write(int fd, off_t pos, const void *buffer, size_t length)
context: user_write(int fd, const void *buffer, off_t pos, size_t length){	struct file_descriptor *descriptor;	ssize_t retval = 0;	CHECK_USER_ADDR(buffer)	descriptor = get_fd(get_current_io_context(false), fd);	if (!descriptor)		return EBADF;	if (descriptor->ops->fd_write) {		retval = descriptor->ops->fd_write(descriptor, buffer, pos, &length);		if (retval >= 0)			retval = (ssize_t)length;	} else		retval = EINVAL;	put_fd(descriptor);	return retval;}