[PATCH] runqemu: Add error handling for unexpected tap devices

[Richard Purdie <richard.purdie@linuxfoundation.org>]

In theory the code reduces the tap device number to an integer. This
patch adds error checking to ensure that does happen and that the script
exits if something unexpected happens.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

diff --git a/scripts/runqemu-internal b/scripts/runqemu-internal
index 03b40d8..0ace485 100755
--- a/scripts/runqemu-internal
+++ b/scripts/runqemu-internal
@@ -253,6 +253,14 @@ else
 
 
         n0=$(echo $TAP | sed 's/tap//')
+
+        case $n0 in
+            ''|*[!0-9]*)
+                echo "Error Couldn't turn $TAP into an interface number?"
+                exit 1
+                ;;
+        esac
+
         n1=$(($n0 * 2 + 1))
         n2=$(($n1 + 1))