[Android Software/Hacking General [Developers Only]] dk_zero-cool:
If you like to play around with the shell on Android, it might come in handy to have some proper hooks for the wifi and dhcp. By default (in custom roms anyway), we have hooks for dhcp. However this does not invoke anything on the dhcp state "STOP". Also there are no hooks for when wifi is turned on, only when dhcp configurations are made to it. Which means that you cannot invoke hooks when turning on/off wifi tethering.

Personally I have an SSHd and SMBd running in the background. These exists as android apps, but I preferer not having android classes running in the background for a such simple task. Specially when I always have these running on wifi. And both SSHd and SMBd works locally on wifi tethering, which is why this hook is a good tool to have.

Also on regular wifi with dhcp, it would be great to have these turn off when wifi connection is off.

The below code will provide these missing features by using some small property hacks in the init.<device>.rc file.

init.<device>.rc

# This provides the missing 'STOP' state invoke in dhcpcd
on property:init.svc.dhcpcd_eth0=stopped
restart dhcpcdstate

# This provides the wifi on/off hook invoke
on property:wlan.driver.status=*
restart wifistate

service dhcpcdstate /system/etc/dhcpcd/dhcpcd-hook STOP eth0
disabled
oneshot

service wifistate /system/etc/wifi/wifi-hook eth0
disabled
oneshot

# ------------------------------------
# The below should be changed according to your device.
# The important thing here is the path to --config and --script

service dhcpcd_eth0 /system/bin/dhcpcd -ABKL --config /system/etc/dhcpcd/dhcpcd.conf --script /system/etc/dhcpcd/dhcpcd-hook
class main
disabled
oneshot

service iprenew_eth0 /system/bin/dhcpcd -n --config /system/etc/dhcpcd/dhcpcd.conf --script /system/etc/dhcpcd/dhcpcd-hook
class main
disabled
oneshot

/system/etc/dhcpcd/dhcpcd-hook

#!/system/bin/sh

if [ -z "${reason}" ] || -z "${interface}"; then
reason="$1"
interface="$2"
fi

for i in /system/etc/dhcpcd/dhcpcd.d/*; do
if [ -f $i ] || [ -L $i ]; then
. "$i"
fi
done

/system/etc/dhcpcd/dhcpcd.d/01-configure

case "${reason}" in
BOUND|INFORM|REBIND|REBOOT|RENEW|TIMEOUT)
setprop dhcp.${interface}.ipaddress "${new_ip_address}"
setprop dhcp.${interface}.gateway "${new_routers%% *}"
setprop dhcp.${interface}.mask "${new_subnet_mask}"
setprop dhcp.${interface}.leasetime "${new_dhcp_lease_time}"
setprop dhcp.${interface}.server "${new_dhcp_server_identifier}"
setprop dhcp.${interface}.ndns "${new_domain_name_servers}"
setprop dhcp.${interface}.reason "${reason}"
setprop dhcp.${interface}.result "ok"

if [ ! -z "${new_domain_name_servers}" ]; then
for i in 1 2 3 4; do
setprop dhcp.${interface}.dns$i ""
done

count=1
for dnsaddr in "${new_domain_name_servers}"; do
setprop dhcp.${interface}.dns$count $dnsaddr
count=$(($count + 1))
done
fi
;;

EXPIRE|FAIL|IPV4LL|RELEASE|STOP)
setprop dhcp.${interface}.result "failed"

for i in 1 2 3 4; do
setprop dhcp.${interface}.dns$i ""
done
;;

RELEASE)
setprop dhcp.${interface}.result "released"
;;
esac

/system/etc/wifi/wifi-hook

#!/system/bin/sh

status=`getprop wlan.driver.status`
interface="$1"

for i in /system/etc/wifi/wifi.d/*; do
if [ -f $i ] || [ -L $i ]; then
. "$i"
fi
done

Change log:

Dec 19, 2011, 21:30 UTC:

Added a altered hook and configure dhcp script

Changed the init.<device>.rc configuration

Added hook for wifi on/off