xen: don't open-code iov_iter_kvec()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/xen/pvcalls-back.c

@@ -134,20 +134,16 @@ static void pvcalls_conn_back_read(void *opaque)
 	masked_cons = pvcalls_mask(cons, array_size);
 
 	memset(&msg, 0, sizeof(msg));
-	msg.msg_iter.type = ITER_KVEC|WRITE;
-	msg.msg_iter.count = wanted;
 	if (masked_prod < masked_cons) {
 		vec[0].iov_base = data->in + masked_prod;
 		vec[0].iov_len = wanted;
-		msg.msg_iter.kvec = vec;
-		msg.msg_iter.nr_segs = 1;
+		iov_iter_kvec(&msg.msg_iter, ITER_KVEC|WRITE, vec, 1, wanted);
 	} else {
 		vec[0].iov_base = data->in + masked_prod;
 		vec[0].iov_len = array_size - masked_prod;
 		vec[1].iov_base = data->in;
 		vec[1].iov_len = wanted - vec[0].iov_len;
-		msg.msg_iter.kvec = vec;
-		msg.msg_iter.nr_segs = 2;
+		iov_iter_kvec(&msg.msg_iter, ITER_KVEC|WRITE, vec, 2, wanted);
 	}
 
 	atomic_set(&map->read, 0);
@@ -196,20 +192,16 @@ static void pvcalls_conn_back_write(struct sock_mapping *map)
 
 	memset(&msg, 0, sizeof(msg));
 	msg.msg_flags |= MSG_DONTWAIT;
-	msg.msg_iter.type = ITER_KVEC|READ;
-	msg.msg_iter.count = size;
 	if (pvcalls_mask(prod, array_size) > pvcalls_mask(cons, array_size)) {
 		vec[0].iov_base = data->out + pvcalls_mask(cons, array_size);
 		vec[0].iov_len = size;
-		msg.msg_iter.kvec = vec;
-		msg.msg_iter.nr_segs = 1;
+		iov_iter_kvec(&msg.msg_iter, ITER_KVEC|READ, vec, 1, size);
 	} else {
 		vec[0].iov_base = data->out + pvcalls_mask(cons, array_size);
 		vec[0].iov_len = array_size - pvcalls_mask(cons, array_size);
 		vec[1].iov_base = data->out;
 		vec[1].iov_len = size - vec[0].iov_len;
-		msg.msg_iter.kvec = vec;
-		msg.msg_iter.nr_segs = 2;
+		iov_iter_kvec(&msg.msg_iter, ITER_KVEC|READ, vec, 2, size);
 	}
 
 	atomic_set(&map->write, 0);