Native Plugin for valume up button

I search all possible threads and do not found any working/understandable information, so i create this thread.

I start with example from there http://docs.unity3d.com/Manual/PluginsForAndroid.html ("Native Plugin Sample")

I want to handle volume up / down buttons on android smartphone.

1. Can you post link to working example of native plugin that handle events?
2. I have tried to add "input.h" library to my .c file, and get next error:
"fatal error: input.h: No such file or directory"
on compilation
my Android.mk file:
include $(CLEAR_VARS)

LOCAL_ARM_MODE := arm
LOCAL_PATH := $(NDK_PROJECT_PATH)
LOCAL_MODULE := libnative
LOCAL_CFLAGS := -Werror
LOCAL_SRC_FILES := NativeCode.c
LOCAL_LDLIBS := -llog -landroid
LOCAL_MODULE := native-activity

include $(BUILD_SHARED_LIBRARY)

How to include system libs?

 

According to the Android documentation (on this page):

What exactly do you want to achieve ? what should the volume up/down buttons do in your game ?

 

It must add additional functionality for android game, as additional key.

 

Did you find a solution?