ceph_tcp_sendpage(): use ITER_BVEC sendmsg

static int ceph_tcp_sendpage(struct socket *sock, struct page *page,

		     int offset, size_t size, bool more)

{

	struct msghdr msg = { .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL };

	struct bio_vec bvec;

	int ret;

	struct kvec iov;

	/* sendpage cannot properly handle pages with page_count == 0,

	 * we need to fallback to sendmsg if that's the case */

	if (page_count(page) >= 1)

		return __ceph_tcp_sendpage(sock, page, offset, size, more);

	iov.iov_base = kmap(page) + offset;

	iov.iov_len = size;

	ret = ceph_tcp_sendmsg(sock, &iov, 1, size, more);

	kunmap(page);

	bvec.bv_page = page;

	bvec.bv_offset = offset;

	bvec.bv_len = size;

	if (more)

		msg.msg_flags |= MSG_MORE;

	else

		msg.msg_flags |= MSG_EOR;  /* superfluous, but what the hell */

	iov_iter_bvec(&msg.msg_iter, WRITE | ITER_BVEC, &bvec, 1, size);

	ret = sock_sendmsg(sock, &msg);

	if (ret == -EAGAIN)

		ret = 0;

	return ret;

}