siw: Inline do_tcp_sendpages()

do_tcp_sendpages() is now just a small wrapper around tcp_sendmsg_locked(),
so inline it, allowing do_tcp_sendpages() to be removed.  This is part of
replacing ->sendpage() with a call to sendmsg() with MSG_SPLICE_PAGES set.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Reviewed-by: Tom Talpey <tom@talpey.com>
cc: Jason Gunthorpe <jgg@ziepe.ca>
cc: Leon Romanovsky <leon@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/infiniband/sw/siw/siw_qp_tx.c

@@ -312,7 +312,7 @@ static int siw_tx_ctrl(struct siw_iwarp_tx *c_tx, struct socket *s,
 }
 
 /*
- * 0copy TCP transmit interface: Use do_tcp_sendpages.
+ * 0copy TCP transmit interface: Use MSG_SPLICE_PAGES.
  *
  * Using sendpage to push page by page appears to be less efficient
  * than using sendmsg, even if data are copied.
@@ -323,20 +323,27 @@ static int siw_tx_ctrl(struct siw_iwarp_tx *c_tx, struct socket *s,
 static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset,
 			     size_t size)
 {
+	struct bio_vec bvec;
+	struct msghdr msg = {
+		.msg_flags = (MSG_MORE | MSG_DONTWAIT | MSG_SENDPAGE_NOTLAST |
+			      MSG_SPLICE_PAGES),
+	};
 	struct sock *sk = s->sk;
-	int i = 0, rv = 0, sent = 0,
-	    flags = MSG_MORE | MSG_DONTWAIT | MSG_SENDPAGE_NOTLAST;
+	int i = 0, rv = 0, sent = 0;
 
 	while (size) {
 		size_t bytes = min_t(size_t, PAGE_SIZE - offset, size);
 
 		if (size + offset <= PAGE_SIZE)
-			flags = MSG_MORE | MSG_DONTWAIT;
+			msg.msg_flags &= ~MSG_SENDPAGE_NOTLAST;
 
 		tcp_rate_check_app_limited(sk);
+		bvec_set_page(&bvec, page[i], bytes, offset);
+		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
+
 try_page_again:
 		lock_sock(sk);
-		rv = do_tcp_sendpages(sk, page[i], offset, bytes, flags);
+		rv = tcp_sendmsg_locked(sk, &msg, size);
 		release_sock(sk);
 
 		if (rv > 0) {