utils: helper script for briding a Qemu instance with the real world

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

utils/bridge-qtap.sh

@@ -0,0 +1,37 @@
+#!/bin/sh
+# Bridge qtap0 and eth2 in qbr0, enabling forwarding of LLDP frames in
+# the group forward mask
+
+TAP=qtap0
+ETH=eth2
+BR=qbr0
+ADDR=192.168.2.1/24
+
+if [ -n "$1" ]; then
+    ETH=$1
+fi
+
+if [ -n "$2" ]; then
+    ADDR=$2
+fi
+
+# https://interestingtraffic.nl/2017/11/21/an-oddly-specific-post-about-group_fwd_mask/
+ip link add qbr0 type bridge group_fwd_mask 0x4000 2>/dev/null
+ip link set "$TAP" master "$BR"
+ip link set "$ETH" master "$BR"
+
+for iface in $ETH $TAP $BR; do
+    ip link set "$iface" up
+done
+
+ip addr flush "$TAP"
+ip addr flush "$ETH"
+ip addr add "$ADDR" dev "$BR" 2>/dev/null
+
+echo "=================="
+ip -br link
+echo "=================="
+ip -br addr
+echo "=================="
+bridge link
+echo "=================="