vring: Better error handling if num is too large

To be more consistent inside this function.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1410329871-28885-3-git-send-email-famz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/virtio/dataplane/vring.c

@@ -181,7 +181,8 @@ static int get_desc(Vring *vring, VirtQueueElement *elem,
 
     /* Stop for now if there are not enough iovecs available. */
     if (*num >= VIRTQUEUE_MAX_SIZE) {
-        return -ENOBUFS;
+        error_report("Invalid SG num: %u", *num);
+        return -EFAULT;
     }
 
     /* TODO handle non-contiguous memory across region boundaries */