libceph: use sock_no_sendpage() as a fallback in ceph_tcp_sendpage()

sock_no_sendpage() makes the code cleaner.

Also, don't set MSG_EOR.  sendpage doesn't act on MSG_EOR on its own,
it just honors the setting from the preceding sendmsg call by looking
at ->eor in tcp_skb_can_collapse_to().
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/messenger.c

@@ -560,24 +560,12 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
 	return r;
 }
 
-static int __ceph_tcp_sendpage(struct socket *sock, struct page *page,
-		     int offset, size_t size, bool more)
-{
-	int flags = MSG_DONTWAIT | MSG_NOSIGNAL | (more ? MSG_MORE : MSG_EOR);
-	int ret;
-
-	ret = kernel_sendpage(sock, page, offset, size, flags);
-	if (ret == -EAGAIN)
-		ret = 0;
-
-	return ret;
-}
-
 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;
+	ssize_t (*sendpage)(struct socket *sock, struct page *page,
+			    int offset, size_t size, int flags);
+	int flags = MSG_DONTWAIT | MSG_NOSIGNAL | (more ? MSG_MORE : 0);
 	int ret;
 
 	/*
@@ -589,19 +577,11 @@ static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
 	 * triggers one of hardened usercopy checks.
 	 */
 	if (page_count(page) >= 1 && !PageSlab(page))
-		return __ceph_tcp_sendpage(sock, page, offset, size, more);
-
-	bvec.bv_page = page;
-	bvec.bv_offset = offset;
-	bvec.bv_len = size;
-
-	if (more)
-		msg.msg_flags |= MSG_MORE;
+		sendpage = sock->ops->sendpage;
 	else
-		msg.msg_flags |= MSG_EOR;  /* superfluous, but what the hell */
+		sendpage = sock_no_sendpage;
 
-	iov_iter_bvec(&msg.msg_iter, WRITE, &bvec, 1, size);
-	ret = sock_sendmsg(sock, &msg);
+	ret = sendpage(sock, page, offset, size, flags);
 	if (ret == -EAGAIN)
 		ret = 0;