Teach configure to check for vhost.h
and disable vhost_net if not present.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>'

---

diff --git a/Makefile.target b/Makefile.target
index 2ebd30c..38783da 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -168,7 +168,8 @@ obj-y = vl.o async.o monitor.o pci.o pci_host.o pcie_host.o machine.o gdbstub.o
 # need to fix this properly
 obj-y += virtio-blk.o virtio-balloon.o virtio-net.o virtio-pci.o virtio-serial-bus.o
 obj-y += notifier.o
-obj-y += vhost_net.o vhost.o
+obj-y += vhost_net.o
+obj-$(CONFIG_VHOST_NET) += vhost.o
 obj-$(CONFIG_KVM) += kvm.o kvm-all.o
 # MSI-X depends on kvm for interrupt injection,
 # so moved it from Makefile.hw to Makefile.target for now
diff --git a/configure b/configure
index 88ba002..4994506 100755
--- a/configure
+++ b/configure
@@ -1510,6 +1510,23 @@ EOF
 fi
 
 ##########################################
+# test for vhost net
+
+if test "$kvm" != "no"; then
+	cat > $TMPC <<EOF
+#include <linux/vhost.h>
+int main(void) { return 0; }
+EOF
+	if compile_prog "$kvm_cflags" "" ; then
+	vhost_net=yes
+	else
+	vhost_net=no
+	fi
+else
+	vhost_net=no
+fi
+
+##########################################
 # libpci probe for kvm_cap_device_assignment
 if test $kvm_cap_device_assignment = "yes" ; then
   cat > $TMPC << EOF
@@ -2058,6 +2075,7 @@ echo "fdt support       $fdt"
 echo "preadv support    $preadv"
 echo "fdatasync         $fdatasync"
 echo "uuid support      $uuid"
+echo "vhost-net support $vhost_net"
 
 if test $sdl_too_old = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -2593,6 +2611,9 @@ case "$target_arch2" in
       if test $kvm_cap_device_assignment = "yes" ; then
         echo "CONFIG_KVM_DEVICE_ASSIGNMENT=y" >> $config_target_mak
       fi
+      if test $vhost_net = "yes" ; then
+        echo "CONFIG_VHOST_NET=y" >> $config_target_mak
+      fi
     fi
 esac
 echo "TARGET_PHYS_ADDR_BITS=$target_phys_bits" >> $config_target_mak
diff --git a/hw/vhost_net.c b/hw/vhost_net.c
index c89ff40..cab9a0a 100644
--- a/hw/vhost_net.c
+++ b/hw/vhost_net.c
@@ -16,9 +16,13 @@
 #include "net/tap.h"
 
 #include "virtio-net.h"
-#include "vhost.h"
 #include "vhost_net.h"
 
+#include "config.h"
+
+#ifdef CONFIG_VHOST_NET
+#include "vhost.h"
+
 struct vhost_net {
 	struct vhost_dev dev;
 	struct vhost_virtqueue vqs[2];
@@ -145,3 +149,31 @@ void vhost_net_cleanup(struct vhost_net *net)
 	qemu_free(net);
 }
 /* TODO: log */
+#else
+struct vhost_net *vhost_net_init(VLANClientState *backend, int devfd)
+{
+	return NULL;
+}
+
+int vhost_net_start(struct vhost_net *net,
+		    VirtIODevice *dev)
+{
+	return -ENOSYS;
+}
+void vhost_net_stop(struct vhost_net *net,
+		    VirtIODevice *dev)
+{
+}
+
+void vhost_net_cleanup(struct vhost_net *net)
+{
+}
+
+unsigned vhost_net_get_features(struct vhost_net *net, unsigned features)
+{
+	return features;
+}
+void vhost_net_ack_features(struct vhost_net *net, unsigned features)
+{
+}
+#endif