xref: /netbsd-src/external/bsd/openresolv/dist/resolvconf.in (revision 59c22029c4938f7f5a598754771a670ab2ba89b8)

#!/bin/sh
# Copyright (c) 2007-2023 Roy Marples
# All rights reserved

# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
#       copyright notice, this list of conditions and the following
#       disclaimer in the documentation and/or other materials provided
#       with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

RESOLVCONF="$0"
OPENRESOLV_VERSION="3.13.2"
SYSCONFDIR=@SYSCONFDIR@
LIBEXECDIR=@LIBEXECDIR@
VARDIR=@VARDIR@
RCDIR=@RCDIR@
RESTARTCMD=@RESTARTCMD@

if [ "$1" = "--version" ]; then
	echo "openresolv $OPENRESOLV_VERSION"
	echo "Copyright (c) 2007-2020 Roy Marples"
	exit 0
fi

# Disregard dhcpcd setting
unset interface_order state_dir

# If you change this, change the test in VFLAG and libc.in as well
local_nameservers="127.* 0.0.0.0 255.255.255.255 ::1"

dynamic_order="tap[0-9]* tun[0-9]* vpn vpn[0-9]* wg[0-9]* ppp[0-9]* ippp[0-9]*"
interface_order="lo lo[0-9]*"
name_server_blacklist="0.0.0.0"

# Support original resolvconf configuration layout
# as well as the openresolv config file
if [ -f "$SYSCONFDIR"/resolvconf.conf ]; then
	. "$SYSCONFDIR"/resolvconf.conf
	[ -n "$state_dir" ] && VARDIR="$state_dir"
elif [ -d "$SYSCONFDIR/resolvconf" ]; then
	SYSCONFDIR="$SYSCONFDIR/resolvconf"
	if [ -f "$SYSCONFDIR"/interface-order ]; then
		interface_order="$(cat "$SYSCONFDIR"/interface-order)"
	fi
fi

IFACEDIR="$VARDIR/interfaces"
METRICDIR="$VARDIR/metrics"
PRIVATEDIR="$VARDIR/private"
EXCLUSIVEDIR="$VARDIR/exclusive"
DEPRECATEDDIR="$VARDIR/deprecated"
LOCKDIR="$VARDIR/lock"
_PWD="$PWD"

warn()
{
	echo "$*" >&2
}

error_exit()
{
	echo "$*" >&2
	exit 1
}

usage()
{
	cat <<-EOF
	Usage: ${RESOLVCONF##*/} [options] command [argument]

	Inform the system about any DNS updates.

	Commands:
	  -a \$INTERFACE    Add DNS information to the specified interface
	                   (DNS supplied via stdin in resolv.conf format)
	  -C \$PATTERN      Deprecate DNS information for matched interfaces
	  -c \$PATTERN      Configure DNS information for matched interfaces
	  -d \$INTERFACE    Delete DNS information from the specified interface
	  -h               Show this help cruft
	  -i [\$PATTERN]    Show interfaces that have supplied DNS information
                   optionally from interfaces that match the specified
                   pattern
	  -l [\$PATTERN]    Show DNS information, optionally from interfaces
	                   that match the specified pattern

	  -u               Run updates from our current DNS information
	  --version        Echo the ${RESOLVCONF##*/} version

	Options:
	  -f               Ignore non existent interfaces
	  -m metric        Give the added DNS information a metric
	  -p               Mark the interface as private
	  -x               Mark the interface as exclusive

	Subscriber and System Init Commands:
	  -I               Init the state dir
	  -r \$SERVICE      Restart the system service
	                   (restarting a non-existent or non-running service
	                    should have no output and return 0)
	  -R               Show the system service restart command
	  -v [\$PATTERN]    echo NEWDOMAIN, NEWSEARCH and NEWNS variables to
	  		   the console
	  -V [\$PATTERN]    Same as -v, but only uses configuration in
	                   $SYSCONFDIR/resolvconf.conf
	EOF
	[ -z "$1" ] && exit 0
	echo
	error_exit "$*"
}

# Strip any trailing dot from each name as a FQDN does not belong
# in resolv.conf(5)
# If you think otherwise, capture a DNS trace and you'll see libc
# will strip it regardless.
# This also solves setting up duplicate zones in our subscribers.
# Also strip any comments denoted by #.
resolv_strip()
{
	space=
	for word; do
		case "$word" in
		\#*) break;;
		esac
		printf "%s%s" "$space${word%.}"
		space=" "
	done
	printf "\n"
}

private_iface()
{
	# Allow expansion
	cd "$IFACEDIR"

	# Public interfaces override private ones.
	for p in $public_interfaces; do
		case "$iface" in
		"$p"|"$p":*) return 1;;
		esac
	done

	if [ -e "$PRIVATEDIR/$iface" ]; then
		return 0
	fi

	for p in $private_interfaces; do
		case "$iface" in
		"$p"|"$p":*) return 0;;
		esac
	done

	# Not a private interface
	return 1
}

# Parse resolv.conf's and make variables
# for domain name servers, search name servers and global nameservers
parse_resolv()
{
	domain=
	new=true
	newns=
	ns=
	private=false
	search=

	while read -r line; do
		stripped_line="$(resolv_strip ${line#* })"
		case "$line" in
		"# resolv.conf from "*)
			if ${new}; then
				iface="${line#\# resolv.conf from *}"
				new=false
				if private_iface "$iface"; then
					private=true
				else
					private=false
				fi
			fi
			;;
		"nameserver "*)
			islocal=false
			for l in $local_nameservers; do
				case "$stripped_line" in
				$l)
					islocal=true
					break
					;;
				esac
			done
			if $islocal; then
				echo "LOCALNAMESERVERS=\"\$LOCALNAMESERVERS $stripped_line\""
			else
				ns="$ns$stripped_line "
			fi
			;;
		"domain "*)
			search="$stripped_line"
			if [ -z "$domain" ]; then
				domain="$search"
				echo "DOMAIN=\"$domain\""
			fi
			;;
		"search "*)
			search="$stripped_line"
			;;
		*)
			[ -n "$line" ] && continue
			if [ -n "$ns" ] && [ -n "$search" ]; then
				newns=
				for n in $ns; do
					newns="$newns${newns:+,}$n"
				done
				ds=
				for d in $search; do
					ds="$ds${ds:+ }$d:$newns"
				done
				echo "DOMAINS=\"\$DOMAINS $ds\""
			fi
			echo "SEARCH=\"\$SEARCH $search\""
			if ! $private; then
				echo "NAMESERVERS=\"\$NAMESERVERS $ns\""
			fi
			ns=
			search=
			new=true
			;;
		esac
	done
}

uniqify()
{
	result=
	while [ -n "$1" ]; do
		case " $result " in
		*" $1 "*);;
		*) result="$result $1";;
		esac
		shift
	done
	echo "${result# *}"
}

dirname()
{
	OIFS="$IFS"
	IFS=/
	set -- $@
	IFS="$OIFS"
	if [ -n "$1" ]; then
		printf %s .
	else
		shift
	fi
	while [ -n "$2" ]; do
		printf "/%s" "$1"
		shift
	done
	printf "\n"
}

config_mkdirs()
{
	for f; do
		[ -n "$f" ] || continue
		d="$(dirname "$f")"
		if [ ! -d "$d" ]; then
			mkdir -p "$d" || return $?
		fi
	done
	return 0
}

# With the advent of alternative init systems, it's possible to have
# more than one installed. So we need to try and guess what one we're
# using unless overridden by configure.
# Note that restarting a service is a last resort - the subscribers
# should make a reasonable attempt to reconfigure the service via some
# method, normally SIGHUP.
detect_init()
{
	[ -n "$RESTARTCMD" ] && return 0

	# Detect the running init system.
	# As systemd and OpenRC can be installed on top of legacy init
	# systems we try to detect them first.
	status="@STATUSARG@"
	: ${status:=status}
	if [ -x /bin/systemctl ] && [ -S /run/systemd/private ]; then
		RESTARTCMD='
			if /bin/systemctl --quiet is-active $1.service
			then
				/bin/systemctl restart $1.service
			fi'
	elif [ -x /usr/bin/systemctl ] && [ -S /run/systemd/private ]; then
		RESTARTCMD='
			if /usr/bin/systemctl --quiet is-active $1.service
			then
				/usr/bin/systemctl restart $1.service
			fi'
	elif [ -x /sbin/rc-service ] &&
	     { [ -s /libexec/rc/init.d/softlevel ] ||
	     [ -s /run/openrc/softlevel ]; }
	then
		RESTARTCMD='/sbin/rc-service -i $1 -- -Ds restart'
	elif [ -x /usr/sbin/invoke-rc.d ]; then
		RCDIR=/etc/init.d
		RESTARTCMD='
		   if /usr/sbin/invoke-rc.d --quiet $1 status >/dev/null 2>&1
		   then
			/usr/sbin/invoke-rc.d $1 restart
		   fi'
	elif [ -x /usr/bin/s6-rc ] && [ -x /usr/bin/s6-svc ]; then
		RESTARTCMD='
		   if s6-rc -a list | grep -qFx $1-srv
		   then
			s6-svc -r /run/service/$1-srv
		   fi'
	elif [ -x /sbin/service ]; then
		# Old RedHat
		RCDIR=/etc/init.d
		RESTARTCMD='
			if /sbin/service $1; then
				/sbin/service $1 restart
			fi'
	elif [ -x /usr/sbin/service ]; then
		# Could be FreeBSD
		RESTARTCMD="
			if /usr/sbin/service \$1 $status >/dev/null 2>&1
			then
				/usr/sbin/service \$1 restart
			fi"
	elif [ -x /bin/sv ]; then
		RESTARTCMD='/bin/sv status $1 >/dev/null 2>&1 &&
			    /bin/sv try-restart $1'
	elif [ -x /usr/bin/sv ]; then
		RESTARTCMD='/usr/bin/sv status $1 >/dev/null 2>&1 &&
			    /usr/bin/sv try-restart $1'
	elif [ -e /etc/arch-release ] && [ -d /etc/rc.d ]; then
		RCDIR=/etc/rc.d
		RESTARTCMD='
			if [ -e /var/run/daemons/$1 ]
			then
				/etc/rc.d/$1 restart
			fi'
	elif [ -e /etc/slackware-version ] && [ -d /etc/rc.d ]; then
		RESTARTCMD='
			if /etc/rc.d/rc.$1 status >/dev/null 2>&1
			then
				/etc/rc.d/rc.$1 restart
			fi'
	elif [ -e /etc/rc.d/rc.subr ] && [ -d /etc/rc.d ]; then
		# OpenBSD
		RESTARTCMD='
			if /etc/rc.d/$1 check >/dev/null 2>&1
			then
				/etc/rc.d/$1 restart
			fi'
	elif [ -d /etc/dinit.d ] && command -v dinitctl >/dev/null 2>&1; then
		RESTARTCMD='dinitctl --quiet restart --ignore-unstarted $1'
	else
		for x in /etc/init.d/rc.d /etc/rc.d /etc/init.d; do
			[ -d $x ] || continue
			RESTARTCMD="
				if $x/\$1 $status >/dev/null 2>&1
				then
					$x/\$1 restart
				fi"
			break
		done
	fi

	if [ -z "$RESTARTCMD" ]; then
		if [ "$_NOINIT_WARNED" != true ]; then
			warn "could not detect a useable init system"
			_NOINIT_WARNED=true
		fi
		return 1
	fi
	_NOINIT_WARNED=
	return 0
}

echo_resolv()
{
	OIFS="$IFS"

	[ -n "$1" ] && [ -f "$IFACEDIR/$1" ] || return 1
	echo "# resolv.conf from $1"
	# Our variable maker works of the fact each resolv.conf per interface
	# is separated by blank lines.
	# So we remove them when echoing them.
	while read -r line; do
		IFS="$OIFS"
		if [ -n "$line" ]; then
			# We need to set IFS here to preserve any whitespace
			IFS=''
			printf "%s\n" "$line"
		fi
	done < "$IFACEDIR/$1"
	IFS="$OIFS"
}

deprecated_interface()
{
	[ -d "$DEPRECATEDDIR" ] || return 1

	cd "$DEPRECATEDDIR"
	for da; do
		for daf in *; do
			[ -f "$daf" ] || continue
			case "$da" in
			$daf) return 0;;
			esac
		done
	done
	return 1
}

list_resolv()
{
	[ -d "$IFACEDIR" ] || return 0

	cmd="$1"
	shift
	pattern_specified="$1"

	excl=false
	list=
	report=false
	retval=0

	case "$IF_EXCLUSIVE" in
	[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
		excl=true
		if [ -d "$EXCLUSIVEDIR" ]; then
			cd "$EXCLUSIVEDIR"
			for i in *; do
				if [ -f "$i" ]; then
					list="${i#* }"
					break
				fi
			done
		fi
		cd "$IFACEDIR"
		for i in $inclusive_interfaces; do
			if [ -f "$i" ] && [ "$list" = "$i" ]; then
				list=
				excl=false
				break
			fi
		done
		;;
	esac

	# If we have an interface ordering list, then use that.
	# It works by just using pathname expansion in the interface directory.
	if [ -n "$pattern_specified" ]; then
		list="$*"
		$force || report=true
	elif ! $excl; then
		cd "$IFACEDIR"

		for i in $interface_order; do
			[ -f "$i" ] && list="$list $i"
			for ii in "$i":* "$i".*; do
				[ -f "$ii" ] && list="$list $ii"
			done
		done

		for i in $dynamic_order; do
			if [ -e "$i" ] && ! [ -e "$METRICDIR/"*" $i" ]; then
				list="$list $i"
			fi
			for ii in "$i":* "$i".*; do
				if [ -f "$ii" ] && ! [ -e "$METRICDIR/"*" $ii" ]
				then
					list="$list $ii"
				fi
			done
		done

		# Interfaces have an implicit metric of 0 if not specified.
		for i in *; do
			if [ -f "$i" ] && ! [ -e "$METRICDIR/"*" $i" ]; then
				list="$list $i"
			fi
		done

		if [ -d "$METRICDIR" ]; then
			cd "$METRICDIR"
			for i in *; do
				[ -f "$i" ] && list="$list ${i#* }"
			done
		fi

		# Move deprecated interfaces to the back
		active=
		deprecated=
		for i in $list; do
			if deprecated_interface "$i"; then
				deprecated="$deprecated $i"
			else
				active="$active $i"
			fi
		done
		list="$active $deprecated"
	fi

	cd "$IFACEDIR"
	if $excl || [ -n "$pattern_specified" ]; then
		retval=1
	else
		retval=0
	fi
	for i in $(uniqify $list); do
		# Only list interfaces which we really have
		if ! [ -f "$i" ]; then
			if $report; then
				echo "No resolv.conf for interface $i" >&2
				retval=2
			fi
			continue
		fi

		if ! $ALLIFACES; then
			if [ -n "$allow_interfaces" ]; then
				x=false
				for j in $allow_interfaces; do
					if [ "$i" = "$j" ]; then
						x=true
					fi
				done
				$x || continue
			fi
			for j in $deny_interfaces; do
				if [ "$i" = "$j" ]; then
					continue 2
				fi
			done
		fi

		if [ "$cmd" = i ] || [ "$cmd" = "-i" ]; then
			printf %s "$i "
		else
			echo_resolv "$i" && echo
		fi
		[ $? = 0 ] && [ "$retval" = 1 ] && retval=0
	done
	[ "$cmd" = i ] || [ "$cmd" = "-i" ] && echo
	return $retval
}

list_remove()
{
	[ -z "$2" ] && return 0
	eval list=\"\$$1\"
	shift
	result=
	retval=0

	set -f
	for e; do
		found=false
		for l in $list; do
			case "$e" in
			$l) found=true;;
			esac
			$found && break
		done
		if $found; then
			retval=$(($retval + 1))
		else
			result="$result $e"
		fi
	done
	set +f
	echo "${result# *}"
	return $retval
}

echo_prepend()
{
	echo "# Generated by resolvconf"
	if [ -n "$search_domains" ]; then
		echo "search $search_domains"
	fi
	for n in $name_servers; do
		echo "nameserver $n"
	done
	echo
}

echo_append()
{
	echo "# Generated by resolvconf"
	if [ -n "$search_domains_append" ]; then
		echo "search $search_domains_append"
	fi
	for n in $name_servers_append; do
		echo "nameserver $n"
	done
	echo
}

replace()
{
	while read -r keyword value; do
		for r in $replace; do
			k="${r%%/*}"
			r="${r#*/}"
			f="${r%%/*}"
			r="${r#*/}"
			v="${r%%/*}"
			case "$keyword" in
			$k)
				case "$value" in
				$f) value="$v";;
				esac
				;;
			esac
		done
		val=
		for sub in $value; do
			for r in $replace_sub; do
				k="${r%%/*}"
				r="${r#*/}"
				f="${r%%/*}"
				r="${r#*/}"
				v="${r%%/*}"
				case "$keyword" in
				$k)
					case "$sub" in
					$f) sub="$v";;
					esac
					;;
				esac
			done
			val="$val${val:+ }$sub"
		done
		printf "%s %s\n" "$keyword" "$val"
	done
}

make_vars()
{
	# Clear variables
	DOMAIN=
	DOMAINS=
	SEARCH=
	NAMESERVERS=
	LOCALNAMESERVERS=

	if [ -n "${name_servers}${search_domains}" ]; then
		eval "$(echo_prepend | parse_resolv)"
	fi
	if [ -z "$VFLAG" ]; then
		IF_EXCLUSIVE=1
		list_resolv -i "$@" >/dev/null || IF_EXCLUSIVE=0
		eval "$(list_resolv -l "$@" | replace | parse_resolv)"
	fi
	if [ -n "${name_servers_append}${search_domains_append}" ]; then
		eval "$(echo_append | parse_resolv)"
	fi

	# Ensure that we only list each domain once
	newdomains=
	for d in $DOMAINS; do
		dn="${d%%:*}"
		list_remove domain_blacklist "$dn" >/dev/null || continue
		case " $newdomains" in
		*" ${dn}:"*) continue;;
		esac
		newns=
		for nd in $DOMAINS; do
			if [ "$dn" = "${nd%%:*}" ]; then
				ns="${nd#*:}"
				while [ -n "$ns" ]; do
					case ",$newns," in
					*,${ns%%,*},*) ;;
					*) list_remove name_server_blacklist \
						"${ns%%,*}" >/dev/null \
					&& newns="$newns${newns:+,}${ns%%,*}";;
					esac
					[ "$ns" = "${ns#*,}" ] && break
					ns="${ns#*,}"
				done
			fi
		done
		if [ -n "$newns" ]; then
			newdomains="$newdomains${newdomains:+ }$dn:$newns"
		fi
	done
	DOMAIN="$(list_remove domain_blacklist $DOMAIN)"
	SEARCH="$(uniqify $SEARCH)"
	SEARCH="$(list_remove domain_blacklist $SEARCH)"
	NAMESERVERS="$(uniqify $NAMESERVERS)"
	NAMESERVERS="$(list_remove name_server_blacklist $NAMESERVERS)"
	LOCALNAMESERVERS="$(uniqify $LOCALNAMESERVERS)"
	LOCALNAMESERVERS="$(list_remove name_server_blacklist $LOCALNAMESERVERS)"
	echo "DOMAIN='$DOMAIN'"
	echo "SEARCH='$SEARCH'"
	echo "NAMESERVERS='$NAMESERVERS'"
	echo "LOCALNAMESERVERS='$LOCALNAMESERVERS'"
	echo "DOMAINS='$newdomains'"
}

force=false
VFLAG=
while getopts a:C:c:Dd:fhIilm:pRruvVx OPT; do
	case "$OPT" in
	f) force=true;;
	h) usage;;
	m) IF_METRIC="$OPTARG";;
	p) IF_PRIVATE=1;;
	V)
		VFLAG=1
		if [ "$local_nameservers" = \
		    "127.* 0.0.0.0 255.255.255.255 ::1" ]
		then
			local_nameservers=
		fi
		;;
	x) IF_EXCLUSIVE=1;;
	'?') exit 1;;
	*) cmd="$OPT"; iface="$OPTARG";;
	esac
done
shift $(($OPTIND - 1))
args="$iface${iface:+ }$*"

# -I inits the state dir
if [ "$cmd" = I ]; then
	if [ -d "$VARDIR" ]; then
		rm -rf "$VARDIR"/*
	fi
	exit $?
fi

# -D ensures that the listed config file base dirs exist
if [ "$cmd" = D ]; then
	config_mkdirs "$@"
	exit $?
fi

# -l lists our resolv files, optionally for a specific interface
if [ "$cmd" = l ] || [ "$cmd" = i ]; then
	ALLIFACES=true
	list_resolv "$cmd" "$args"
	exit $?
fi
ALLIFACES=false

# Restart a service or echo the command to restart a service
if [ "$cmd" = r ] || [ "$cmd" = R ]; then
	detect_init || exit 1
	if [ "$cmd" = r ]; then
		set -- $args
		eval "$RESTARTCMD"
	else
		echo "$RESTARTCMD" |
			sed -e '/^$/d' -e 's/^			//g'
	fi
	exit $?
fi

# Not normally needed, but subscribers should be able to run independently
if [ "$cmd" = v ] || [ -n "$VFLAG" ]; then
	make_vars "$iface"
	exit $?
fi

# Test that we have valid options
case "$cmd" in
a|d|C|c)
	if [ -z "$iface" ]; then
		error_exit "Interface not specified"
	fi
	;;
u)	;;
*)
	if [ -n "$cmd" ] && [ "$cmd" != h ]; then
		error_exit "Unknown option $cmd"
	fi
	usage
	;;
esac

if [ "$cmd" = a ]; then
	for x in '/' \\ ' ' '*'; do
		case "$iface" in
		*[$x]*) error_exit "$x not allowed in interface name";;
		esac
	done
	for x in '.' '-' '~'; do
		case "$iface" in
		[$x]*) error_exit \
			"$x not allowed at start of interface name";;
		esac
	done
	[ "$cmd" = a ] && [ -t 0 ] && error_exit "No file given via stdin"
fi

if [ ! -d "$VARDIR" ]; then
	if [ -L "$VARDIR" ]; then
		dir="$(readlink "$VARDIR")"
		# link maybe relative
		cd "${VARDIR%/*}"
		if ! mkdir -m 0755 -p "$dir"; then
			error_exit "Failed to create needed" \
				"directory $dir"
		fi
	else
		if ! mkdir -m 0755 -p "$VARDIR"; then
			error_exit "Failed to create needed" \
				"directory $VARDIR"
		fi
	fi
fi

if [ ! -d "$IFACEDIR" ]; then
	mkdir -m 0755 -p "$IFACEDIR" || \
		error_exit "Failed to create needed directory $IFACEDIR"
	if [ "$cmd" = d ]; then
		# Provide the same error messages as below
		if ! ${force}; then
			cd "$IFACEDIR"
			for i in $args; do
				warn "No resolv.conf for interface $i"
			done
		fi
		${force}
		exit $?
	fi
fi

# An interface was added, changed, deleted or a general update was called.
# Due to exclusivity we need to ensure that this is an atomic operation.
# Our subscribers *may* need this as well if the init system is sub par.
# As such we spinlock at this point as best we can.
# We don't use flock(1) because it's not widely available and normally resides
# in /usr which we do our very best to operate without.
[ -w "$VARDIR" ] || error_exit "Cannot write to $LOCKDIR"
: ${lock_timeout:=10}
: ${clear_nopids:=5}
have_pid=false
had_pid=false
while true; do
	if mkdir "$LOCKDIR" 2>/dev/null; then
		trap 'rm -rf "$LOCKDIR";' EXIT
		trap 'rm -rf "$LOCKDIR"; exit 1' INT QUIT ABRT SEGV ALRM TERM
		echo $$ >"$LOCKDIR/pid"
		break
	fi
	pid=$(cat "$LOCKDIR/pid" 2>/dev/null)
	if [ "$pid" -gt 0 ] 2>/dev/null; then
		have_pid=true
		had_pid=true
	else
		have_pid=false
		clear_nopids=$(($clear_nopids - 1))
		if [ "$clear_nopids" -le 0 ]; then
			warn "not seen a pid, clearing lock directory"
			rm -rf "$LOCKDIR"
		else
			lock_timeout=$(($lock_timeout - 1))
			sleep 1
		fi
		continue
	fi
	if $have_pid && ! kill -0 "$pid"; then
		warn "clearing stale lock pid $pid"
		rm -rf "$LOCKDIR"
		continue
	fi
	lock_timeout=$(($lock_timeout - 1))
	if [ "$lock_timeout" -le 0 ]; then
		if $have_pid; then
			error_exit "timed out waiting for lock from pid $pid"
		else
			if $had_pid; then
				error_exit "timed out waiting for lock" \
					"from some pids"
			else
				error_exit "timed out waiting for lock"
			fi
		fi
	fi
	sleep 1
done
unset have_pid had_pid clear_nopids

case "$cmd" in
a)
	# Read resolv.conf from stdin
	resolv="$(cat)"
	changed=false
	changedfile=false
	# If what we are given matches what we have, then do nothing
	if [ -e "$IFACEDIR/$iface" ]; then
		if [ "$(echo "$resolv")" != \
			"$(cat "$IFACEDIR/$iface")" ]
		then
			changed=true
			changedfile=true
		fi
	else
		changed=true
		changedfile=true
	fi

	# Set metric and private before creating the interface resolv.conf file
	# to ensure that it will have the correct flags
	[ ! -d "$METRICDIR" ] && mkdir "$METRICDIR"
	oldmetric="$METRICDIR/"*" $iface"
	newmetric=
	if [ -n "$IF_METRIC" ]; then
		# Pad metric to 6 characters, so 5 is less than 10
		while [ ${#IF_METRIC} -le 6 ]; do
			IF_METRIC="0$IF_METRIC"
		done
		newmetric="$METRICDIR/$IF_METRIC $iface"
	fi
	rm -f "$METRICDIR/"*" $iface"
	[ "$oldmetric" != "$newmetric" ] &&
	    [ "$oldmetric" != "$METRICDIR/* $iface" ] &&
		changed=true
	[ -n "$newmetric" ] && echo " " >"$newmetric"

	case "$IF_PRIVATE" in
	[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
		if [ ! -d "$PRIVATEDIR" ]; then
			[ -e "$PRIVATEDIR" ] && rm "$PRIVATEDIR"
			mkdir "$PRIVATEDIR"
		fi
		[ -e "$PRIVATEDIR/$iface" ] || changed=true
		[ -d "$PRIVATEDIR" ] && echo " " >"$PRIVATEDIR/$iface"
		;;
	*)
		if [ -e "$PRIVATEDIR/$iface" ]; then
			rm -f "$PRIVATEDIR/$iface"
			changed=true
		fi
		;;
	esac

	oldexcl=
	for x in "$EXCLUSIVEDIR/"*" $iface"; do
		if [ -f "$x" ]; then
			oldexcl="$x"
			break
		fi
	done
	case "$IF_EXCLUSIVE" in
	[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
		if [ ! -d "$EXCLUSIVEDIR" ]; then
			[ -e "$EXCLUSIVEDIR" ] && rm "$EXCLUSIVEDIR"
			mkdir "$EXCLUSIVEDIR"
		fi
		cd "$EXCLUSIVEDIR"
		for x in *; do
			[ -f "$x" ] && break
		done
		if [ "${x#* }" != "$iface" ]; then
			if [ "$x" = "${x% *}" ]; then
				x=10000000
			else
				x="${x% *}"
			fi
			if [ "$x" = "0000000" ]; then
				warn "exclusive underflow"
			else
				x=$(($x - 1))
			fi
			if [ -d "$EXCLUSIVEDIR" ]; then
				echo " " >"$EXCLUSIVEDIR/$x $iface"
			fi
			changed=true
		fi
		;;
	*)
		if [ -f "$oldexcl" ]; then
			rm -f "$oldexcl"
			changed=true
		fi
		;;
	esac

	if $changedfile; then
		printf "%s\n" "$resolv" >"$IFACEDIR/$iface" || exit $?
	elif ! $changed; then
		exit 0
	fi
	unset changed changedfile oldmetric newmetric x oldexcl
	;;

d)
	# Delete any existing information about the interface
	cd "$IFACEDIR"
	changed=false
	for i in $args; do
		if [ -e "$i" ]; then
			changed=true
		elif ! ${force}; then
			warn "No resolv.conf for interface $i"
		fi
		rm -f "$i" "$METRICDIR/"*" $i" \
			"$PRIVATEDIR/$i" \
			"$EXCLUSIVEDIR/"*" $i" || exit $?
	done

	if ! $changed; then
		# Set the return code based on the forced flag
		$force
		exit $?
	fi
	unset changed i
	;;

C)
	# Mark interface as deprecated
	[ ! -d "$DEPRECATEDDIR" ] && mkdir "$DEPRECATEDDIR"
	cd "$DEPRECATEDDIR"
	changed=false
	for i in $args; do
		if [ ! -e "$i" ]; then
			changed=true
			echo " " >"$i" || exit $?
		fi
	done
	$changed || exit 0
	unset changed i
	;;

c)
	# Mark interface as active
	if [ -d "$DEPRECATEDDIR" ]; then
		cd "$DEPRECATEDDIR"
		changed=false
		for i in $args; do
			if [ -e "$i" ]; then
				changed=true
				rm "$i" || exit $?
			fi
		done
		$changed || exit 0
		unset changed i
	fi
	;;
esac

case "${resolvconf:-YES}" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1) ;;
*) exit 0;;
esac

# Try and detect a suitable init system for our scripts
detect_init
export RESTARTCMD RCDIR _NOINIT_WARNED

eval "$(make_vars)"
export RESOLVCONF DOMAINS SEARCH NAMESERVERS LOCALNAMESERVERS
: ${list_resolv:=list_resolv -l}
retval=0

# Run scripts in the same directory resolvconf is run from
# in case any scripts accidentally dump files in the wrong place.
cd "$_PWD"
for script in "$LIBEXECDIR"/*; do
	if [ -f "$script" ]; then
		eval script_enabled="\$${script##*/}"
		case "${script_enabled:-YES}" in
		[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1) ;;
		*) continue;;
		esac
		if [ -x "$script" ]; then
			"$script" "$cmd" "$iface"
		else
			(set -- "$cmd" "$iface"; . "$script")
		fi
		retval=$(($retval + $?))
	fi
done
exit $retval