AOSP dhcpcd-6.8.2 how to run hooks

Since Android 7, AOSP dhcpcd (standard dhcp client) was replaced by dhcpcd-6.8.2 that is, reading in Android.mk, a “D-Bus enabled and compatible with Brillo daemons” dhcp client based on dhcpcd: let’s see how it should be customized for running hooks after completing some actions.

For my tests I’m using the Hikey960, even though there should not be almost anything board related in the next steps besides package availability: in fact dhcpcd does not belong to the default packages of the Hikey build, so it should be added.

Open the device makefile (device/linaro/hikey/hikey960/device-hikey960.mk) and add the following line:

PRODUCT_PACKAGES += dhcpcd-6.8.2

After a successful build the package is ready to be used (generally through the definition of a service), but, by default, it won’t run any hook.

Taking a look at the Android makefile (external/dhcpcd-6.8.2/Android.mk) we can see the interesting symbol DHCPCD_USE_SCRIPT: this should be set to ‘yes’ to enable hook execution, so add the line

DHCPCD_USE_SCRIPT := yes

after the first instance of LOCAL_PATH

Now you need two other elements:

The bash script used for running the hooks
The hooks to be run

The first one could be easily generated using the standard makefile: open a shell in the dhcpcd directory and type

$ make dhcpcd-run-hooks

to create a script called dhcpcd-run-hooks used for running the hooks.

However, with my setup it was not properly working as it was generated, so I had to customize the path of sh: instead of

#!/bin/sh

for the Hikey960 it was

#!/system/bin/sh

I had also to modify the hooks directory in the following block

for hook in \
    /dhcpcd.enter-hook \
    /dhcpcd-hooks/* \
    /dhcpcd.exit-hook

e.g. in my system I placed the hooks in /system/etc/dhcpcd/dhcpcd-hooks, so the block becomes

for hook in \
    /system/etc/dhcpcd/dhcpcd.enter-hook \
    /system/etc/dhcpcd/dhcpcd-hooks/* \
    /system/etc/dhcpcd/dhcpcd.exit-hook

Some hooks can be found in

external/dhcpcd-6.8.2/dhcpcd-hooks

Choose the needed ones (or create a new one): I find especially useful 50-dhcpcd-compat.

Once identified the hooks you need, the Android makefile should be changed for copying the right files in the filesystem. Android.mk has the following commented part:

# Each build target using dhcpcd-6.8.2 should define its own source
# and destination for its dhcpcd.conf file.
# include $(CLEAR_VARS)
# LOCAL_MODULE := dhcpcd-6.8.2.conf
# LOCAL_MODULE_CLASS := ETC
# LOCAL_MODULE_PATH := $(TARGET_OUT)/etc/dhcpcd-6.8.2
# LOCAL_SRC_FILES := android.conf
# include $(BUILD_PREBUILT)

We can use similar lines for copying the hooks running script and the needed hooks, like the following

include $(CLEAR_VARS)
 LOCAL_MODULE := dhcpcd-run-hooks
 LOCAL_MODULE_CLASS := EXECUTABLES
 LOCAL_MODULE_PATH := $(TARGET_OUT_ETC)/dhcpcd
 LOCAL_SRC_FILES := $(LOCAL_MODULE)
 include $(BUILD_PREBUILT)

include $(CLEAR_VARS)
 LOCAL_MODULE := 50-dhcpcd-compat
 LOCAL_MODULE_CLASS := ETC
 LOCAL_MODULE_PATH := $(TARGET_OUT_ETC)/dhcpcd/dhcpcd-hooks
 LOCAL_SRC_FILES := dhcpcd/$(LOCAL_MODULE)
 include $(BUILD_PREBUILT)

Do not forget to set the executability bit to the various scripts, add the new created packages, rebuild and you should have your hooks properly working.