examples: add example of a DHCP server

As usual, by multiplying directories - "dhcpd_eth0", "dhcpd_wlan1"
you can run many servers on different interfaces.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

examples/var_service/dhcpd_if/README

@@ -0,0 +1,5 @@
+The real README file is one directory up.
+
+This directory's run script can have useful comments.
+If it doesn't but you feel it should, please send a patch
+to busybox's mailing list.

examples/var_service/dhcpd_if/log/run

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+user=logger
+
+logdir="/var/log/service/`(cd ..;basename $PWD)`"
+mkdir -p "$logdir" 2>/dev/null
+chown -R "$user": "$logdir"
+chmod -R go-rwxst,u+rwX "$logdir"
+rm -rf logdir
+ln -s "$logdir" logdir
+
+# make this dir accessible to logger
+chmod a+rX .
+
+exec >/dev/null
+exec 2>&1
+exec \
+env - PATH="$PATH" \
+softlimit \
+setuidgid "$user" \
+svlogd -tt "$logdir"

examples/var_service/dhcpd_if/p_log

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+cd log/logdir || exit 1
+cat @* current | $PAGER

examples/var_service/dhcpd_if/run

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+exec 2>&1
+exec </dev/null
+
+pwd="$PWD"
+
+if="${PWD##*/dhcpd_}"
+
+echo "* Upping iface $if"
+ip link set dev $if up
+
+>>udhcpd.leases
+sed 's/^interface.*$/interface '"$if/" -i udhcpc.conf
+
+echo "* Starting udhcpd"
+exec \
+env - PATH="$PATH" \
+softlimit \
+setuidgid root \
+udhcpd -f -vv udhcpc.conf
+
+exit $?

examples/var_service/dhcpd_if/udhcpc.conf

@@ -0,0 +1,28 @@
+# Directives with defaults:
+# start		192.168.0.20
+# end		192.168.0.254
+# interface	eth0
+# max_leases	235
+# auto_time	7200
+# decline_time	3600
+# conflict_time	3600
+# offer_time	60
+# min_lease	60
+# lease_file	/var/lib/misc/udhcpd.leases
+# pidfile	/var/run/udhcpd.pid
+# siaddr	0.0.0.0
+#
+# Directives with no defaults (or with empty defaults):
+# option/opt	NAME VALUE
+# notify_file	/path/to/script_to_run_after_leasefile_is_written
+#		(it is run with $1 = lease_file_name)
+# sname		dhcp_packet_sname_field_contents
+# boot_file	dhcp_packet_bootfile_field_contents
+# static_lease	XX:XX:XX:XX:XX:XX IP.ADD.RE.SS
+
+interface if
+pidfile		/dev/null
+lease_file	udhcpd.leases
+option		subnet 255.255.255.0
+option		lease  3600
+#option		router 192.168.0.1

examples/var_service/dhcpd_if/w_dumpleases

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+watch -n1 'dumpleases -af udhcpd.leases'

examples/var_service/dhcpd_if/w_dumpleases_countdown

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+watch -n1 'dumpleases -f udhcpd.leases'

examples/var_service/dhcpd_if/w_log

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+cd log/logdir
+watch -n1 'w=`ttysize w`; h=`ttysize h`; tail -$((h-3)) current 2>&1 | cut -b0-$((w-2))'