From c7e4237da098389ad6273242371d1b5af546f4d4 Mon Sep 17 00:00:00 2001
From: "B. Watson" <yalhcru@gmail.com>
Date: Sun, 24 Mar 2019 19:50:23 -0400
Subject: simplify start_slip script

---
 src/start_slip.sh | 62 ++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 12 deletions(-)

diff --git a/src/start_slip.sh b/src/start_slip.sh
index 8a9320a..5126756 100755
--- a/src/start_slip.sh
+++ b/src/start_slip.sh
@@ -1,18 +1,32 @@
 #!/bin/sh
 
-# Configurable stuff:
+# Configurable stuff. You only ever need to change the IP addresses
+# if your LAN already uses 192.168.0.0/24.
 
 TTY=/dev/ttyUSB0       # serial port to use
-BAUD=9600              # must match compiled-in value in rs232dev.c
-SLATTACH=a8_slattach   # slattach binary (possibly patched)
-SLIP_IFACE=sl0         # probably no need to change this
-LOCAL_IP=192.168.0.1   # SLIP IP address for Linux host
+BAUD=9600              # must match baud rate in fujichat.cfg on the Atari
+LOCAL_IP=192.168.0.1   # SLIP IP address for Linux ("peer") host
 REMOTE_IP=192.168.0.2  # SLIP IP address for Atari host
-IP_FORWARD=yes         # Route packets for the Atari?
+
+# You want these two enabled, unless you're running an IRC server locally,
+# and don't want to connect FujiChat to the real Internet:
+IP_FORWARD=yes         # Route packets for the Atari? (you want this, unless
+                       # you're running an IRC server locally)
 IP_MASQUERADE=yes      # NAT for the Atari?
-MASQ_IFACE=eth1        # if NATing, our main (LAM or internet) interface
 DUMP_PACKETS=yes       # Run tcpdump on sl0 interface?
 
+# Optional. Autodetected, if you leave these commented out (recommended).
+
+#SLATTACH=a8_slattach  # slattach binary (possibly patched). if not set,
+                       # search $PATH for a8_slattach, then fall back to
+                       # regular slattach.
+
+#MASQ_IFACE=eth1       # if NATing, our main (LAM or internet) interface
+                       # (if not set, detect automagically)
+
+#SLIP_IFACE=sl0        # don't change this unless you know exactly why
+                       # you need to!
+
 # DELAY may not be needed on all systems...
 
 # No delay:
@@ -26,11 +40,25 @@ DELAY="usleep 250000"
 
 # End of config section, start of code:
 
-ifconfig $SLIP_IFACE down 2&>/dev/null
-killall $SLATTACH 2&>/dev/null
-fuser -k $TTY 2&>/dev/null # make sure nobody's using the port...
+# Just in case:
+/sbin/modprobe slip 2>/dev/null
+
+if [ "$SLATTACH" = "" ]; then
+	SLATTACH="$( which a8_slattach 2>/dev/null )"
+	if [ "$SLATTACH" = "" ]; then
+		SLATTACH="$( which slattach 2>/dev/null )"
+	fi
+fi
+echo "Using SLATTACH=$SLATTACH"
+
+# Warning: this assumes nothing else is using SLIP. Probably a safe
+# assumption in the 21st century.
+SLIP_IFACE="${SLIP_IFACE:-sl0}"
+ifconfig $SLIP_IFACE down 2>/dev/null
+killall $SLATTACH 2>/dev/null
+fuser -k $TTY 2>/dev/null # make sure nobody's using the port...
 $DELAY
-fuser -k -9 $TTY 2&>/dev/null # Just in case...
+fuser -k -9 $TTY 2>/dev/null # Just in case...
 $DELAY
 
 echo "Starting SLIP on $SLIP_IFACE, local $LOCAL_IP, remote $REMOTE_IP"
@@ -40,7 +68,17 @@ ifconfig $SLIP_IFACE $LOCAL_IP mtu 576
 ifconfig $SLIP_IFACE $LOCAL_IP pointopoint $REMOTE_IP
 
 if [ "$IP_MASQUERADE" = "yes" ]; then
-	echo "IP Masquerading enabled"
+	if [ "$MASQ_IFACE" = "" ]; then
+		/sbin/ip route show 2>/dev/null | sed -n 's,^default.*dev *\([^ ]*\).*$,\1,p'
+		if [ "$MASQ_IFACE" = "" ]; then
+			/sbin/route -n | grep '^0.0.0.0' | rev | cut -d' ' -f1 |rev
+			if [ "$MASQ_IFACE" = "" ]; then
+				echo "Can't autodetect default interface, guessing eth0"
+				MASQ_IFACE="eth0"
+			fi
+		fi
+	fi
+	echo "IP Masquerading enabled on device $MASQ_IFACE"
 	iptables -F
 	iptables -t nat -F
 	iptables -t nat -A POSTROUTING -o $MASQ_IFACE -j MASQUERADE
-- 
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