snagrecover: am335x_usb_setup.sh: Improve POSIX-compliance

This is part of an effort to make this script work better with different
user shells, such as fish shell which previously couldn't run this script.

Remove bashisms and change method for creating recovery shell. Use sh
instead of bash for the recovery shell.

Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>

src/snagrecover/am335x_usb_setup.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 # This file is part of Snagboot
 # Copyright (C) 2023 Bootlin
 #
@@ -17,24 +17,23 @@
 # You should have received a copy of the GNU General Public License
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
-: '
-This script will do the following things to setup
-an environment for recovering an AM335x soc via USB:
-1. Create a new network namespace called $NETNS_NAME
-2. Run a subprocess that will trigger every time
-   a new ROM code or SPL USB ethernet gadget with a
-   certain PID:VID pair is registered.
-   It will:
-   2.1. Move the network interface to $NETNS_NAME
-   2.2. Add a static IP address to the interface,
-       so that the board can reach the recovery tool
-   2.3. Route an arbitrary client ip to the interface,
-       so that the recovery tool can reach the board
-   3.4. Route 255.255.255.255 to the interface, so
-   	that the recovery tool can reach the board
-	using a broadcast, when the board does not
-	know its own IP yet
-'
+
+# This script will do the following things to setup
+# an environment for recovering an AM335x soc via USB:
+# 1. Create a new network namespace called $NETNS_NAME
+# 2. Run a subprocess that will trigger every time
+#    a new ROM code or SPL USB ethernet gadget with a
+#    certain PID:VID pair is registered.
+#    It will:
+#    2.1. Move the network interface to $NETNS_NAME
+#    2.2. Add a static IP address to the interface,
+#        so that the board can reach the recovery tool
+#    2.3. Route an arbitrary client ip to the interface,
+#        so that the recovery tool can reach the board
+#    3.4. Route 255.255.255.255 to the interface, so
+#         that the recovery tool can reach the board
+#         using a broadcast, when the board does not
+#         know its own IP yet
 
 print_usage () {
 	echo "am335x_usb_setup.sh: Create network namespace and udev rules necessary for AM335x USB recovery"
@@ -54,25 +53,23 @@ print_usage () {
 fail_on_error () {
 	echo "ERROR: $1" >> /dev/stderr
 	echo "Operation failed" >> /dev/stderr
-	exit -1
+	exit 1
 }
 
 DEFAULT_ROMUSB="0451:6141"
 DEFAULT_SPLUSB="0451:d022"
-SCRIPTPATH="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
 NETNS_NAME="snagbootnet"
 SUDOER="$SUDO_USER"
 SUDOER_BASHRC=$(eval echo "~$SUDOER")"/.bashrc"
-CUSTOM_RCFILE=". $SUDOER_BASHRC; export PS1='(am335_recovery) \u@\h:\w \$ '"
 poller_id=""
 
 #delete the new network namespace and udev rules
 cleanup () {
-	if [ ! "$poller_id" == "" ]; then
+	if [ ! "$poller_id" = "" ]; then
 		kill -KILL $poller_id
 	fi
 	echo "Deleting namespace $NETNS_NAME..."
-	ip netns delete $NETNS_NAME
+	ip netns delete "$NETNS_NAME"
 }
 
 config_interface () {
@@ -84,14 +81,14 @@ config_interface () {
 	IF_NAME=$1
 
 	#move interface to recovery network namespace
-	ip link set $IF_NAME down
-	ip link set $IF_NAME netns $NETNS_NAME
-	ip netns exec $NETNS_NAME ip link set $IF_NAME up
+	ip link set "$IF_NAME" down
+	ip link set "$IF_NAME" netns "$NETNS_NAME"
+	ip netns exec "$NETNS_NAME" ip link set "$IF_NAME" up
 
 	#assign static ip to interface, setup ip route
-	ip netns exec $NETNS_NAME ip addr add dev $IF_NAME $SERVER_IP
-	ip netns exec $NETNS_NAME ip route add "255.255.255.255" dev $IF_NAME
-	ip netns exec $NETNS_NAME ip route add $CLIENT_IP dev $IF_NAME
+	ip netns exec "$NETNS_NAME" ip addr add dev "$IF_NAME" "$SERVER_IP"
+	ip netns exec "$NETNS_NAME" ip route add "255.255.255.255" dev "$IF_NAME"
+	ip netns exec "$NETNS_NAME" ip route add "$CLIENT_IP" dev "$IF_NAME"
 }
 
 
@@ -106,19 +103,19 @@ while getopts "r:s:n:ch:" opt; do
     h) print_usage
       exit 0
       ;;
-    *) echo "Invalid option: -$OPTARG" >&2
+    :) echo "Option -$OPTARG requires an argument." >&2
       print_usage
-      exit -1
+      exit 1
       ;;
-    :) echo "Option -$OPTARG requires an argument." >&2
+    *) echo "Invalid option: -$OPTARG" >&2
       print_usage
-      exit -1
+      exit 1
       ;;
   esac
 done
 
 #check user
-if [ ! "$(whoami)" == "root" ]; then
+if [ ! "$(whoami)" = "root" ]; then
 	fail_on_error "This script should be run as root!"
 fi
 
@@ -128,9 +125,11 @@ if [ -z "${SUDOER}" ]; then
 fi
 
 id "$SUDOER" >/dev/null 2>&1; code=$?
-if [ $code -eq 1 ] || [ "$SUDOER" == "root" ]; then
+if [ $code -eq 1 ] || [ "$SUDOER" = "root" ]; then
 	# SUDO_USER may not work on all systems ...
-	SUDOER="$(ps -o user= -p $(ps -o ppid= -p $(ps -o ppid= -p $$)))"
+	PARENT_ID=$(ps -o ppid= -p $$)
+	GRANDPARENT_ID=$(ps -o ppid= -p $PARENT_ID)
+	SUDOER=$(ps -o user= -p $GRANDPARENT_ID)
 	id "$SUDOER" >/dev/null 2>&1; code=$?
 	if [ $code -eq 1 ] || [ "$SUDOER" = "root" ]; then
 		fail_on_error "Failed to find the username of sudo caller: found $SUDOER"
@@ -142,28 +141,30 @@ if [ ! -f "$SUDOER_BASHRC" ]; then
 fi
 
 #check usb args
-usb_regex="^[[:xdigit:]]{4}:[[:xdigit:]]{4}$"
-if [[ ! "$ROMUSB" =~ $usb_regex ]]; then
+USB_REGEX="^[[:xdigit:]]{4}:[[:xdigit:]]{4}$"
+if ! echo "$ROMUSB" | grep -qE "$USB_REGEX"; then
 	echo "Missing -r flag or invalid format for ROM USB gadget address vid:pid, using default value"
 	ROMUSB=$DEFAULT_ROMUSB
 fi
-if [[ ! "$SPLUSB" =~ $usb_regex ]]; then
+if ! echo "$SPLUSB" | grep -qE "$USB_REGEX"; then
 	echo "Missing -s flag or invalid format for SPL USB gadget address vid:pid, using default value"
 	SPLUSB=$DEFAULT_SPLUSB
 fi
+
 #strip leading zeroes and replace colons with slashes
-ROMUSB=$(echo -n "$ROMUSB/" | sed -e 's/^0*//' -e 's/:0*/:/' -e 's/:/\//')
-SPLUSB=$(echo -n "$SPLUSB/" | sed -e 's/^0*//' -e 's/:0*/:/' -e 's/:/\//')
+ROMUSB=$(printf "%s/" "$ROMUSB" | sed -e 's/^0*//' -e 's/:0*/:/' -e 's/:/\//')
+SPLUSB=$(printf "%s/" "$SPLUSB" | sed -e 's/^0*//' -e 's/:0*/:/' -e 's/:/\//')
 
 echo "Starting polling subprocess..."
+
 poll_interface () {
-	ROMNETFILE=$(grep -s -l "PRODUCT=$ROMUSB" $(grep -s -l "DEVTYPE=usb_interface" /sys/class/net/*/device/uevent))
-	SPLNETFILE=$(grep -s -l "PRODUCT=$SPLUSB" $(grep -s -l "DEVTYPE=usb_interface" /sys/class/net/*/device/uevent))
-	if [ -e "$ROMNETFILE" ]; then
-		config_interface  "$(echo $ROMNETFILE | cut -d '/' -f 5)" >/dev/null 2>&1
-	fi
-	if [ -e "$SPLNETFILE" ]; then
-		config_interface  "$(echo $SPLNETFILE | cut -d '/' -f 5)" >/dev/null 2>&1
+	UEVENTS=$(grep -s -l "DEVTYPE=usb_interface" /sys/class/net/*/device/uevent)
+	ROMNETDEV=$(grep -s -l "PRODUCT=$ROMUSB" $UEVENTS | cut -d '/' -f 5)
+	SPLNETDEV=$(grep -s -l "PRODUCT=$SPLUSB" $UEVENTS | cut -d '/' -f 5)
+	if [ -n "$ROMNETDEV" ]; then
+		config_interface  "$ROMNETDEV" >/dev/null 2>&1
+	elif [ -n "$SPLNETDEV" ]; then
+		config_interface  "$SPLNETDEV" >/dev/null 2>&1
 	fi
 }
 
@@ -179,20 +180,20 @@ if test -f "/run/netns/$NETNS_NAME"; then
 	fail_on_error "The network namespace $NETNS_NAME already exists! Cancelling operation..."
 fi
 echo "Creating network namespace $NETNS_NAME..."
-ip netns add $NETNS_NAME || fail_on_error "Could not create namespace $NETNS_NAME"
+ip netns add "$NETNS_NAME" || fail_on_error "Could not create namespace $NETNS_NAME"
 
 #iptables rules
-ip netns exec $NETNS_NAME iptables -t nat -A PREROUTING -p udp --dport 67 -j DNAT --to-destination :9067
-ip netns exec $NETNS_NAME iptables -t nat -A PREROUTING -p udp --dport 69 -j DNAT --to-destination :9069
-ip netns exec $NETNS_NAME iptables -t nat -A POSTROUTING -p udp --sport 9067 -j MASQUERADE --to-ports 67
-ip netns exec $NETNS_NAME iptables -t nat -A POSTROUTING -p udp --sport 9069 -j MASQUERADE --to-ports 69
+ip netns exec "$NETNS_NAME" iptables -t nat -A PREROUTING -p udp --dport 67 -j DNAT --to-destination :9067
+ip netns exec "$NETNS_NAME" iptables -t nat -A PREROUTING -p udp --dport 69 -j DNAT --to-destination :9069
+ip netns exec "$NETNS_NAME" iptables -t nat -A POSTROUTING -p udp --sport 9067 -j MASQUERADE --to-ports 67
+ip netns exec "$NETNS_NAME" iptables -t nat -A POSTROUTING -p udp --sport 9069 -j MASQUERADE --to-ports 69
 
 #start new shell
-echo -e "Logging user $SUDOER into new shell\n"
+printf "Logging user %s into new shell\n" "$SUDOER"
 echo "===== $NETNS_NAME ====="
 echo "You can now setup the board and run the recovery tool."
 echo "Please type 'exit' to delete the namespace, stop the polling process and leave the shell when you are done."
-ip netns exec $NETNS_NAME su $SUDOER --session-command "bash --rcfile <(echo \"$CUSTOM_RCFILE\")"
+SUDO_PS1='(am335_recovery) \u@\h:\w \$' ip netns exec "$NETNS_NAME" sudo -i -u "$SUDOER" sh
 
 #leave shell and cleanup
 cleanup