[PATCH 2/2] tools/virtio: vringh_test: check that a split ring must be a power of two

[Stjepan Poljak <stjepan.poljak@gmail.com>]

vring_new_virtqueue() used to accept a split ring of any size, although
the ring is indexed with num - 1 as a mask. Check that it now refuses
one size short of RINGSIZE.

Without the preceding fix, vringh_test fails with:

  vringh_test: vring_new_virtqueue accepted size 255

With it, vring_new_virtqueue() prints "Bad virtqueue length 255" and the
rest of the test runs as before.

Signed-off-by: Stjepan Poljak <stjepan.poljak@gmail.com>
---
 tools/virtio/vringh_test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c
index 2a5d7f7d2d6c..75c66385502d 100644
--- a/tools/virtio/vringh_test.c
+++ b/tools/virtio/vringh_test.c
@@ -494,6 +494,17 @@ int main(int argc, char *argv[])
 	__user_addr_max = __user_addr_min + USER_MEM;
 	memset(__user_addr_min, 0, vring_size(RINGSIZE, ALIGN));
 
+	/*
+	 * The split ring indexes its rings with num - 1 as a mask, so a
+	 * size that is not a power of two must be refused.
+	 */
+	vq = vring_new_virtqueue(0, RINGSIZE - 1, ALIGN, &vdev, true, false,
+				 __user_addr_min,
+				 never_notify_host, never_callback_guest,
+				 "guest vq");
+	if (vq)
+		errx(1, "vring_new_virtqueue accepted size %u", RINGSIZE - 1);
+
 	/* Set up guest side. */
 	vq = vring_new_virtqueue(0, RINGSIZE, ALIGN, &vdev, true, false,
 				 __user_addr_min,
-- 
2.53.0