espintcp: 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>
cc: Steffen Klassert <steffen.klassert@secunet.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: David Ahern <dsahern@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/xfrm/espintcp.c

@@ -205,14 +205,16 @@ static int espintcp_sendskb_locked(struct sock *sk, struct espintcp_msg *emsg,
 static int espintcp_sendskmsg_locked(struct sock *sk,
 				     struct espintcp_msg *emsg, int flags)
 {
+	struct msghdr msghdr = { .msg_flags = flags | MSG_SPLICE_PAGES, };
 	struct sk_msg *skmsg = &emsg->skmsg;
 	struct scatterlist *sg;
 	int done = 0;
 	int ret;
 
-	flags |= MSG_SENDPAGE_NOTLAST;
+	msghdr.msg_flags |= MSG_SENDPAGE_NOTLAST;
 	sg = &skmsg->sg.data[skmsg->sg.start];
 	do {
+		struct bio_vec bvec;
 		size_t size = sg->length - emsg->offset;
 		int offset = sg->offset + emsg->offset;
 		struct page *p;
@@ -220,11 +222,13 @@ static int espintcp_sendskmsg_locked(struct sock *sk,
 		emsg->offset = 0;
 
 		if (sg_is_last(sg))
-			flags &= ~MSG_SENDPAGE_NOTLAST;
+			msghdr.msg_flags &= ~MSG_SENDPAGE_NOTLAST;
 
 		p = sg_page(sg);
 retry:
-		ret = do_tcp_sendpages(sk, p, offset, size, flags);
+		bvec_set_page(&bvec, p, size, offset);
+		iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
+		ret = tcp_sendmsg_locked(sk, &msghdr, size);
 		if (ret < 0) {
 			emsg->offset = offset - sg->offset;
 			skmsg->sg.start += done;