vhost-net-vdpa: add stubs for when no virtio-net device is present

net/vhost-vdpa.c will need functions that are declared in
vhost-shadow-virtqueue.c, that needs functions of virtio-net.c.

Copy the vhost-vdpa-stub.c code so
only the constructor net_init_vhost_vdpa needs to be defined.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/meson.build

@@ -41,7 +41,8 @@ endif
 softmmu_ss.add(when: 'CONFIG_POSIX', if_true: files(tap_posix))
 softmmu_ss.add(when: 'CONFIG_WIN32', if_true: files('tap-win32.c'))
 if have_vhost_net_vdpa
-  softmmu_ss.add(files('vhost-vdpa.c'))
+  softmmu_ss.add(when: 'CONFIG_VIRTIO_NET', if_true: files('vhost-vdpa.c'), if_false: files('vhost-vdpa-stub.c'))
+  softmmu_ss.add(when: 'CONFIG_ALL', if_true: files('vhost-vdpa-stub.c'))
 endif
 
 vmnet_files = files(

net/vhost-vdpa-stub.c

@@ -0,0 +1,21 @@
+/*
+ * vhost-vdpa-stub.c
+ *
+ * Copyright (c) 2022 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "clients.h"
+#include "net/vhost-vdpa.h"
+#include "qapi/error.h"
+
+int net_init_vhost_vdpa(const Netdev *netdev, const char *name,
+                        NetClientState *peer, Error **errp)
+{
+    error_setg(errp, "vhost-vdpa requires frontend driver virtio-net-*");
+    return -1;
+}