tools/virtio: add noring tool

Useful to measure testing framework overhead.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/ringtest/Makefile

 all:
 
-all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder
+all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder noring
 
 CFLAGS += -Wall
 CFLAGS += -pthread -O2 -ggdb
@@ -15,11 +15,13 @@ ring: ring.o main.o
 virtio_ring_0_9: virtio_ring_0_9.o main.o
 virtio_ring_poll: virtio_ring_poll.o main.o
 virtio_ring_inorder: virtio_ring_inorder.o main.o
+noring: noring.o main.o
 clean:
 	-rm main.o
 	-rm ring.o ring
 	-rm virtio_ring_0_9.o virtio_ring_0_9
 	-rm virtio_ring_poll.o virtio_ring_poll
 	-rm virtio_ring_inorder.o virtio_ring_inorder
+	-rm noring.o noring
 
 .PHONY: all clean

tools/virtio/ringtest/noring.c

+#define _GNU_SOURCE
+#include "main.h"
+#include <assert.h>
+
+/* stub implementation: useful for measuring overhead */
+void alloc_ring(void)
+{
+}
+
+/* guest side */
+int add_inbuf(unsigned len, void *buf, void *datap)
+{
+	return 0;
+}
+
+/*
+ * skb_array API provides no way for producer to find out whether a given
+ * buffer was consumed.  Our tests merely require that a successful get_buf
+ * implies that add_inbuf succeed in the past, and that add_inbuf will succeed,
+ * fake it accordingly.
+ */
+void *get_buf(unsigned *lenp, void **bufp)
+{
+	return "Buffer";
+}
+
+void poll_used(void)
+{
+}
+
+void disable_call()
+{
+	assert(0);
+}
+
+bool enable_call()
+{
+	assert(0);
+}
+
+void kick_available(void)
+{
+	assert(0);
+}
+
+/* host side */
+void disable_kick()
+{
+	assert(0);
+}
+
+bool enable_kick()
+{
+	assert(0);
+}
+
+void poll_avail(void)
+{
+}
+
+bool use_buf(unsigned *lenp, void **bufp)
+{
+	return true;
+}
+
+void call_used(void)
+{
+	assert(0);
+}