systemd/extras/rule_generator/write_net_rules

#!/bin/sh -e
#
# Copyright (C) 2006 Marco d'Itri <md@Linux.IT>
# Copyright (C) 2007 Kay Sievers <kay.sievers@vrfy.org>
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation version 2 of the License.
#
# This script is run to create persistent network device naming rules
# based on properties of the device.
# If the interface needs to be renamed, INTERFACE_NEW=<name> will be printed
# on stdout to allow udev to IMPORT it.

# variables used to communicate:
#   MATCHADDR             MAC address used for the match
#   MATCHID               bus_id used for the match
#   MATCHDRV              driver name used for the match
#   MATCHIFTYPE           interface type match
#   COMMENT               comment to add to the generated rule
#   INTERFACE_NAME        requested name supplied by external tool
#   INTERFACE_NEW         new interface name returned by rule writer

RULES_FILE='/etc/udev/rules.d/70-persistent-net.rules'

. /lib/udev/rule_generator.functions

interface_name_taken() {
	local value="$(find_all_rules 'NAME=' $INTERFACE)"
	if [ "$value" ]; then
		return 0
	else
		return 1
	fi
}

find_next_available() {
	raw_find_next_available "$(find_all_rules 'NAME=' "$1")"
}

write_rule() {
	local match="$1"
	local name="$2"
	local comment="$3"

	{
	if [ "$PRINT_HEADER" ]; then
		PRINT_HEADER=
		echo "# This file was automatically generated by the $0"
		echo "# program run by the persistent-net-generator.rules rules file."
		echo "#"
		echo "# You can modify it, as long as you keep each rule on a single line."
	fi

	echo ""
	[ "$comment" ] && echo "# $comment"
	echo "SUBSYSTEM==\"net\", ACTION==\"add\"$match, NAME=\"$name\""
	} >> $RULES_FILE
}

if [ -z "$INTERFACE" ]; then
	echo "missing \$INTERFACE" >&2
	exit 1
fi

# Prevent concurrent processes from modifying the file at the same time.
lock_rules_file

# Check if the rules file is writeable.
choose_rules_file

# the DRIVERS key is needed to not match bridges and VLAN sub-interfaces
if [ "$MATCHADDR" ]; then
	match="$match, DRIVERS==\"?*\", ATTR{address}==\"$MATCHADDR\""
fi

if [ "$MATCHDRV" ]; then
	match="$match, DRIVERS==\"$MATCHDRV\""
fi

if [ "$MATCHID" ]; then
	match="$match, KERNELS==\"$MATCHID\""
fi

if [ "$MATCHIFTYPE" ]; then
	match="$match, ATTR{type}==\"$MATCHIFTYPE\""
fi

if [ -z "$match" ]; then
	echo "missing valid match" >&2
	unlock_rules_file
	exit 1
fi

if [ "$INTERFACE_NAME" ]; then
	# external tools may request a custom name
	COMMENT="$COMMENT (custom name provided by external tool)"
	if [ "$INTERFACE_NAME" != "$INTERFACE" ]; then
		INTERFACE=$INTERFACE_NAME;
		echo "INTERFACE_NEW=$INTERFACE"
	fi
else
	# if a rule using the current name already exists, find a new name
	basename=${INTERFACE%%[0-9]*}
	match="$match, KERNEL==\"$basename*\""
	if interface_name_taken; then
		INTERFACE="$basename$(find_next_available "$basename[0-9]*")"
		echo "INTERFACE_NEW=$INTERFACE"
	fi
fi

write_rule "$match" "$INTERFACE" "$COMMENT"

unlock_rules_file

exit 0