[nbd] pass iov_iter to nbd_xmit()

... and don't mess with kmap() - just use BVEC_ITER for those parts.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/block/nbd.c

@@ -209,13 +209,12 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 /*
  *  Send or receive packet.
  */
-static int sock_xmit(struct nbd_device *nbd, int index, int send, void *buf,
-		     int size, int msg_flags)
+static int sock_xmit(struct nbd_device *nbd, int index, int send,
+		     struct iov_iter *iter, int msg_flags)
 {
 	struct socket *sock = nbd->socks[index]->sock;
 	int result;
 	struct msghdr msg;
-	struct kvec iov = {.iov_base = buf, .iov_len = size};
 	unsigned long pflags = current->flags;
 
 	if (unlikely(!sock)) {
@@ -225,8 +224,7 @@ static int sock_xmit(struct nbd_device *nbd, int index, int send, void *buf,
 		return -EINVAL;
 	}
 
-	iov_iter_kvec(&msg.msg_iter, (send ? WRITE : READ) | ITER_KVEC,
-		      &iov, 1, size);
+	msg.msg_iter = *iter;
 
 	current->flags |= PF_MEMALLOC;
 	do {
@@ -254,28 +252,21 @@ static int sock_xmit(struct nbd_device *nbd, int index, int send, void *buf,
 	return result;
 }
 
-static inline int sock_send_bvec(struct nbd_device *nbd, int index,
-				 struct bio_vec *bvec, int flags)
-{
-	int result;
-	void *kaddr = kmap(bvec->bv_page);
-	result = sock_xmit(nbd, index, 1, kaddr + bvec->bv_offset,
-			   bvec->bv_len, flags);
-	kunmap(bvec->bv_page);
-	return result;
-}
-
 /* always call with the tx_lock held */
 static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 {
 	struct request *req = blk_mq_rq_from_pdu(cmd);
 	int result, flags;
-	struct nbd_request request;
+	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
+	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
+	struct iov_iter from;
 	unsigned long size = blk_rq_bytes(req);
 	struct bio *bio;
 	u32 type;
 	u32 tag = blk_mq_unique_tag(req);
 
+	iov_iter_kvec(&from, WRITE | ITER_KVEC, &iov, 1, sizeof(request));
+
 	if (req_op(req) == REQ_OP_DISCARD)
 		type = NBD_CMD_TRIM;
 	else if (req_op(req) == REQ_OP_FLUSH)
@@ -285,8 +276,6 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 	else
 		type = NBD_CMD_READ;
 
-	memset(&request, 0, sizeof(request));
-	request.magic = htonl(NBD_REQUEST_MAGIC);
 	request.type = htonl(type);
 	if (type != NBD_CMD_FLUSH) {
 		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
@@ -297,7 +286,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
 		cmd, nbdcmd_to_ascii(type),
 		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
-	result = sock_xmit(nbd, index, 1, &request, sizeof(request),
+	result = sock_xmit(nbd, index, 1, &from,
 			(type == NBD_CMD_WRITE) ? MSG_MORE : 0);
 	if (result <= 0) {
 		dev_err_ratelimited(disk_to_dev(nbd->disk),
@@ -322,7 +311,9 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 				flags = MSG_MORE;
 			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
 				cmd, bvec.bv_len);
-			result = sock_send_bvec(nbd, index, &bvec, flags);
+			iov_iter_bvec(&from, ITER_BVEC | WRITE,
+				      &bvec, 1, bvec.bv_len);
+			result = sock_xmit(nbd, index, 1, &from, flags);
 			if (result <= 0) {
 				dev_err(disk_to_dev(nbd->disk),
 					"Send data failed (result %d)\n",
@@ -343,17 +334,6 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 	return 0;
 }
 
-static inline int sock_recv_bvec(struct nbd_device *nbd, int index,
-				 struct bio_vec *bvec)
-{
-	int result;
-	void *kaddr = kmap(bvec->bv_page);
-	result = sock_xmit(nbd, index, 0, kaddr + bvec->bv_offset,
-			   bvec->bv_len, MSG_WAITALL);
-	kunmap(bvec->bv_page);
-	return result;
-}
-
 /* NULL returned = something went wrong, inform userspace */
 static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 {
@@ -363,9 +343,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 	struct request *req = NULL;
 	u16 hwq;
 	u32 tag;
+	struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
+	struct iov_iter to;
 
 	reply.magic = 0;
-	result = sock_xmit(nbd, index, 0, &reply, sizeof(reply), MSG_WAITALL);
+	iov_iter_kvec(&to, READ | ITER_KVEC, &iov, 1, sizeof(reply));
+	result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL);
 	if (result <= 0) {
 		if (!test_bit(NBD_DISCONNECTED, &nbd->runtime_flags) &&
 		    !test_bit(NBD_DISCONNECT_REQUESTED, &nbd->runtime_flags))
@@ -405,7 +388,9 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 		struct bio_vec bvec;
 
 		rq_for_each_segment(bvec, req, iter) {
-			result = sock_recv_bvec(nbd, index, &bvec);
+			iov_iter_bvec(&to, ITER_BVEC | READ,
+				      &bvec, 1, bvec.bv_len);
+			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL);
 			if (result <= 0) {
 				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
 					result);
@@ -645,14 +630,17 @@ static void nbd_parse_flags(struct nbd_device *nbd, struct block_device *bdev)
 
 static void send_disconnects(struct nbd_device *nbd)
 {
-	struct nbd_request request = {};
+	struct nbd_request request = {
+		.magic = htonl(NBD_REQUEST_MAGIC),
+		.type = htonl(NBD_CMD_DISC),
+	};
+	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
+	struct iov_iter from;
 	int i, ret;
 
-	request.magic = htonl(NBD_REQUEST_MAGIC);
-	request.type = htonl(NBD_CMD_DISC);
-
 	for (i = 0; i < nbd->num_connections; i++) {
-		ret = sock_xmit(nbd, i, 1, &request, sizeof(request), 0);
+		iov_iter_kvec(&from, WRITE | ITER_KVEC, &iov, 1, sizeof(request));
+		ret = sock_xmit(nbd, i, 1, &from, 0);
 		if (ret <= 0)
 			dev_err(disk_to_dev(nbd->disk),
 				"Send disconnect failed %d\n", ret);