From c21cab05f8c188b52aa2b9832420d726e60aef87 Mon Sep 17 00:00:00 2001
From: SDD <sdd@local>
Date: Sat, 17 Oct 2026 14:15:17 +0300
Subject: [PATCH] harness: net-setup.sh -- recreate the tap+bridge the harness
 needs (they do not survive a reboot)

---
 harness/net-setup.sh | 60 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100755 harness/net-setup.sh

diff --git a/harness/net-setup.sh b/harness/net-setup.sh
new file mode 100755
index 0000000..1e85876
--- /dev/null
+++ b/harness/net-setup.sh
@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+# net-setup.sh -- create the tap + bridge the VT1200 harness needs on the host.
+#
+# Idempotent: safe to re-run, and NEEDS re-running after a reboot, because both
+# the tap and the bridge are runtime kernel state and do not survive one.
+#
+#   ./harness/net-setup.sh
+#
+# The tap is owned by your user, which is what lets MAME attach to it with no
+# sudo and no capabilities of its own.  The bridge gets an address so the host
+# can serve BOOTP and TFTP to the terminal.
+#
+# IMPORTANT: both interfaces will still show DOWN until MAME opens the tap.  A
+# tap has carrier only while a process holds it open, and a bridge whose only
+# port has no carrier reports down.  That is correct, not a failure.
+
+set -euo pipefail
+
+UID_="$(id -u)"
+USER_="$(id -un)"
+TAP="tap-mess-${UID_}-0"          # MAME's own naming: taptun.cpp, "tap-mess-%d-0"
+BRIDGE="vt1200"
+ADDR="192.168.99.1/24"
+
+if ! sudo -n true 2>/dev/null; then
+    echo "net-setup: needs passwordless sudo (or run these by hand):" >&2
+    echo "  ip tuntap add dev $TAP mode tap user $USER_" >&2
+    echo "  ip link add dev $BRIDGE type bridge" >&2
+    exit 1
+fi
+
+if ip link show "$TAP" >/dev/null 2>&1; then
+    echo "net-setup: $TAP exists, leaving it"
+else
+    sudo -n ip tuntap add dev "$TAP" mode tap user "$USER_"
+    echo "net-setup: created $TAP (owned by $USER_)"
+fi
+
+if ip link show "$BRIDGE" >/dev/null 2>&1; then
+    echo "net-setup: $BRIDGE exists, leaving it"
+else
+    sudo -n ip link add dev "$BRIDGE" type bridge
+    echo "net-setup: created $BRIDGE"
+fi
+
+sudo -n ip link set "$TAP" master "$BRIDGE"
+sudo -n ip link set "$TAP" up
+sudo -n ip link set "$BRIDGE" up
+# single-member bridge: no STP, so it forwards immediately instead of after ~30s
+sudo -n ip link set "$BRIDGE" type bridge stp_state 0
+sudo -n ip addr replace "$ADDR" dev "$BRIDGE"
+
+echo
+echo "host side now:"
+ip -brief addr show "$BRIDGE" | sed 's/^/  /'
+ip -brief link show "$TAP" | sed 's/^/  /'
+echo
+echo "reminder: both read DOWN until MAME holds the tap. Then run, in another shell:"
+echo "  sudo python3 -u harness/serve.py 192.168.99.1 --bootp"
+echo "  ./run.sh net"