http://blog.csdn.net/eliot_shao/article/details/51861905
http://blog.csdn.net/eliot_shao/article/details/51864811
HAL层中文名称又叫硬件抽象层，可以理解我Linux驱动的应用层。本文实现了一个简单的hello HAL的代码，衔接hello驱动和hello JNI：
http://blog.csdn.net/eliot_shao/article/details/51860229
Android标准架构实例分析之编写最简单的hello驱动
HAL层的代码会使用open read write等系统调用操作驱动层的文件系统（dev、sysfs、proc），同时它也有自己的数据结构，为上层提供接口，并导出和本体模块相关ID号。上层可以使用hw_get_module获得HAL中写的方法。其实如果不是为了避开Linux的GPL开源协议，HAL层可以不用，直接使用JNI层或者在Java代码中访问操作驱动层的文件系统（dev、sysfs、proc）也是可行的。
详细原理可以参考：
http://blog.csdn.net/eliot_shao/article/details/50461738
HAL代码编写的基本步骤
1、编写HAL层头文件
2、填充相关的结构体
1、编写HAL层头文件
首先我们要知道关于HAL的三点要求：
1、 每一个hardware硬件模块都有一个ID；
2、 每一个hardware模块必须有一个继承struct hw_module_t common;的结构体；
3、 每一个hardware模块必须有一个继承struct hw_device_t common;的结构体；
struct hw_module_t的继承者担负了“联络员”的任务，在/system/lib/hw下面有若干hardware module，本地框架层通过ID找到对应的模块。
struct hw_device_t的继承者承担了对驱动操作方法的包装的任务。
struct hw_module_t和struct hw_device_t的内容定义在：
hardware\libhardware\include\hardware\hardware.h
所以我们的hello.h内容如下：
#ifndef ANDROID_HELLO_INTERFACE_H2、填充相关的结构体
我们总结一下硬件具体的调用流程，也是hardware层的工作流程：
1、 通过ID找到硬件模块，struct hw_module_t common的结构体的继承者；
2、 通过硬件模块找到hw_module_methods_t，打开操作，获得设备的hw_device_t；
3、 调用hw_device_t中的各种操作硬件的方法；
4、 调用完成，通过hw_device_t的close关闭设备。
HAL规定了需要创一个名为HAL_MODULE_INFO_SYM结构体，如下：
struct hello_module_t HAL_MODULE_INFO_SYM = {
.common = {
.tag= HARDWARE_MODULE_TAG,
//.module_api_version = FINGERPRINT_MODULE_API_VERSION_2_0,
.hal_api_version= HARDWARE_HAL_API_VERSION,
.id = HELLO_HARDWARE_MODULE_ID,
.name = "Demo shaomingliang hello HAL",
.author = "The Android Open Source Project",
.methods= &hello_module_methods,
},
};
填充struct hw_module_t common 并对其成员 methods进行赋值：
.methods= &hello_module_methods,
hello_module_methods的定义如下：
static struct hw_module_methods_t hello_module_methods = {
.open = hello_device_open,
};
在 hello_device_open 对 struct hello_device_t 进行填充。
下面是抽象层hello.c的详细代码：
#define LOG_TAG "HelloStub"
#include <hardware/hardware.h>
#include <hardware/hello.h>
#include <sys/mman.h>
#include <dlfcn.h>
#include <cutils/ashmem.h>
#include <cutils/log.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <string.h>
#include <stdlib.h>
#include <cutils/log.h>
#include <cutils/atomic.h>
#define MODULE_NAME "Hello"
char const * const device_name = "/dev/hello" ;
static int hello_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device);
static int hello_device_close(struct hw_device_t* device);
static int hello_set_val(struct hello_device_t* dev, int val);
static int hello_get_val(struct hello_device_t* dev, int* val);
static struct hw_module_methods_t hello_module_methods = {
.open = hello_device_open,
};
static int hello_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device)
{
struct hello_device_t* dev;
char name_[64];
//pthread_mutex_t lock;
dev = (struct hello_device_t*)malloc(sizeof(struct hello_device_t));
if(!dev) {
ALOGE("Hello Stub: failed to alloc space");
return -EFAULT;
}
ALOGE("Hello Stub: hello_device_open eliot_shao");
memset(dev, 0, sizeof(struct hello_device_t));
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (hw_module_t*)module;
dev->common.close = hello_device_close;
dev->set_val = hello_set_val;
dev->get_val = hello_get_val;
//pthread_mutex_lock(&lock);
dev->fd = -1 ;
snprintf(name_, 64, device_name, 0);
dev->fd = open(name_, O_RDWR);
if(dev->fd == -1) {
ALOGE("Hello Stub:eliot failed to open %s !-- %s.", name_,strerror(errno));
free(dev);
return -EFAULT;
}
//pthread_mutex_unlock(&lock);
*device = &(dev->common);
ALOGI("Hello Stub: open HAL hello successfully.");
return 0;
}
static int hello_device_close(struct hw_device_t* device) {
struct hello_device_t* hello_device = (struct hello_device_t*)device;
if(hello_device) {
close(hello_device->fd);
free(hello_device);
}
return 0;
}
static int hello_set_val(struct hello_device_t* dev, int val) {
ALOGI("Hello Stub: set value to device.");
write(dev->fd, &val, sizeof(val));
return 0;
}
static int hello_get_val(struct hello_device_t* dev, int* val) {
if(!val) {
ALOGE("Hello Stub: error val pointer");
return -EFAULT;
}
read(dev->fd, val, sizeof(*val));
ALOGI("Hello Stub: get value from device");
return 0;
}
struct hello_module_t HAL_MODULE_INFO_SYM = {
.common = {
.tag = HARDWARE_MODULE_TAG,
//.module_api_version = FINGERPRINT_MODULE_API_VERSION_2_0,
.hal_api_version = HARDWARE_HAL_API_VERSION,
.id = HELLO_HARDWARE_MODULE_ID,
.name = "Demo shaomingliang hello HAL",
.author = "The Android Open Source Project",
.methods = &hello_module_methods,
},
};
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Android.mk 的详细代码如下：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := hello.default
LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_SRC_FILES := hello.c
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_MODULE_TAGS := optional
include $(BUILD_SHARED_LIBRARY)
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hello HAL代码的编译
将hal的代码放到如下位置：
hardware\libhardware\modules\hello\hello.c
hardware\libhardware\modules\hello\Android.mk
hardware\libhardware\include\hardware\hello.h
执行：mmm hardware\libhardware\modules\hello\
将会在system/lib/hw/下生成一个hello.default.so!
摘要：
Android JNI是一种技术，提供Java调用Android native代码或者native调用Java代码的一种机制，并不提供策略。
JNI原理分析
首先上一张Android JNI技术的工作原理图：
在图中主要描述Java-jni-native的一个调用流程。下面进行按步骤讲解：
1、Java代码通过System.loadLibrary(“android_servers”); 加载JNI静态库；
2、Android runtime自动调用JNI静态库中的JNI_OnLoad函数；
3、JNI_OnLoad调用jniRegisterNativeMethods函数，注册多个或者一个JNINativeMethod到Android runtime的gMthods链表中；
4、Java代码声明并调用相关的native代码；
5、Android runtime查找gMthods链表找到前面注册的本地函数指针，然后执行。
注意：JNI和HAL的衔接是通过JNI的代码
hw_get_module(HELLO_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0)
实现的。
本文使用的hello的案例是以system_server进程上建立的，后面会创建一个hello的本地服务。下面是对system_server进程调用JNI过程进行分析。
1、frameworks\base\services\java\com\android\server\SystemServer.java
// Initialize native services.
System.loadLibrary("android_servers");
2、frameworks\base\services\core\jni\onload.cpp
jint JNI_OnLoad(JavaVM* vm, void* /* reserved */)
register_android_server_HelloService(env);//add by eliot_shao
3、frameworks\base\services\core\jni\com_android_server_HelloService.cpp
jniRegisterNativeMethods(env, "com/android/server/HelloService", method_table, NELEM(method_table));
static const JNINativeMethod method_table[] = {
{"init_native", "()Z", (void*)hello_init},
{"setVal_native", "(I)V", (void*)hello_setVal},
{"getVal_native", "()I", (void*)hello_getVal},
};
4、frameworks\base\services\Android.mk
LOCAL_MODULE:= libandroid_servers
hello JNI实例
rameworks\base\services\core\jni\com_android_server_HelloService.cpp
#define LOG_TAG "HelloService"
#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"
#include <utils/misc.h>
#include <utils/Log.h>
#include <hardware/hardware.h>
#include <hardware/hello.h>
#include <stdio.h>
namespace android
{
struct hello_device_t* hello_device = NULL;
static void hello_setVal(JNIEnv* env, jobject clazz, jint value) {
int val = value;
ALOGI("Hello JNI: set value %d to device.", val);
if(!hello_device) {
ALOGI("Hello JNI: device is not open.");
return;
}
hello_device->set_val(hello_device, val);
}
static jint hello_getVal(JNIEnv* env, jobject clazz) {
int val = 0;
if(!hello_device) {
ALOGI("Hello JNI: device is not open.");
return val;
}
hello_device->get_val(hello_device, &val);
ALOGI("Hello JNI: get value %d from device.", val);
return val;
}
static inline int hello_device_open(const hw_module_t* module, struct hello_device_t** device) {
return module->methods->open(module, HELLO_HARDWARE_MODULE_ID, (struct hw_device_t**)device);
}
static jboolean hello_init(JNIEnv* env, jclass clazz) {
hello_module_t* module;
ALOGI("Hello JNI: initializing......");
if(hw_get_module(HELLO_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0) {
ALOGI("Hello JNI: hello Stub found.");
if(hello_device_open(&(module->common), &hello_device) == 0) {
ALOGI("Hello JNI: hello device is open.");
return 0;
}
ALOGE("Hello JNI: failed to open hello device.");
return -1;
}
ALOGE("Hello JNI: failed to get hello stub module.");
return -1;
}
static const JNINativeMethod method_table[] = {
{"init_native", "()Z", (void*)hello_init},
{"setVal_native", "(I)V", (void*)hello_setVal},
{"getVal_native", "()I", (void*)hello_getVal},
};
int register_android_server_HelloService(JNIEnv *env) {
return jniRegisterNativeMethods(env, "com/android/server/HelloService", method_table, NELEM(method_table));
}
};
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frameworks\base\services\core\jni\onload.cpp
/*
* Copyright (C) 2014 MediaTek Inc.
* Modification based on code covered by the mentioned copyright
* and/or permission notice(s).
*/
/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "JNIHelp.h"
#include "jni.h"
#include "utils/Log.h"
#include "utils/misc.h"
namespace android {
int register_android_server_AlarmManagerService(JNIEnv* env);
int register_android_server_AssetAtlasService(JNIEnv* env);
int register_android_server_BatteryStatsService(JNIEnv* env);
int register_android_server_ConsumerIrService(JNIEnv *env);
int register_android_server_InputApplicationHandle(JNIEnv* env);
int register_android_server_InputWindowHandle(JNIEnv* env);
int register_android_server_InputManager(JNIEnv* env);
int register_android_server_LightsService(JNIEnv* env);
int register_android_server_PowerManagerService(JNIEnv* env);
int register_android_server_SerialService(JNIEnv* env);
int register_android_server_SystemServer(JNIEnv* env);
int register_android_server_UsbDeviceManager(JNIEnv* env);
int register_android_server_UsbMidiDevice(JNIEnv* env);
int register_android_server_UsbHostManager(JNIEnv* env);
int register_android_server_VibratorService(JNIEnv* env);
int register_android_server_location_GpsLocationProvider(JNIEnv* env);
int register_android_server_location_FlpHardwareProvider(JNIEnv* env);
int register_android_server_connectivity_Vpn(JNIEnv* env);
int register_android_server_hdmi_HdmiCecController(JNIEnv* env);
int register_android_server_tv_TvInputHal(JNIEnv* env);
int register_android_server_PersistentDataBlockService(JNIEnv* env);
int register_android_server_Watchdog(JNIEnv* env);
int register_com_mediatek_perfservice_PerfServiceManager(JNIEnv* env);
#if defined (MTK_HDMI_SUPPORT)
int register_com_mediatek_hdmi_MtkHdmiManagerService(JNIEnv* env);
#endif
// Mediatek AAL support
int register_android_server_display_DisplayPowerController(JNIEnv* env);
#ifndef MTK_BSP_PACKAGE
int register_com_android_internal_app_ShutdownManager(JNIEnv *env);
#endif
int register_android_server_HelloService(JNIEnv *env);//add by eliot_shao
};
using namespace android;
extern "C" jint JNI_OnLoad(JavaVM* vm, void* /* reserved */)
{
JNIEnv* env = NULL;
jint result = -1;
if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
ALOGE("GetEnv failed!");
return result;
}
ALOG_ASSERT(env, "Could not retrieve the env!");
register_android_server_PowerManagerService(env);
register_android_server_SerialService(env);
register_android_server_InputApplicationHandle(env);
register_android_server_InputWindowHandle(env);
register_android_server_InputManager(env);
register_android_server_LightsService(env);
register_android_server_AlarmManagerService(env);
register_android_server_UsbDeviceManager(env);
register_android_server_UsbMidiDevice(env);
register_android_server_UsbHostManager(env);
register_android_server_VibratorService(env);
register_android_server_SystemServer(env);
register_android_server_location_GpsLocationProvider(env);
register_android_server_location_FlpHardwareProvider(env);
register_android_server_connectivity_Vpn(env);
register_android_server_AssetAtlasService(env);
register_android_server_ConsumerIrService(env);
register_android_server_BatteryStatsService(env);
register_android_server_hdmi_HdmiCecController(env);
register_android_server_tv_TvInputHal(env);
register_android_server_PersistentDataBlockService(env);
register_android_server_Watchdog(env);
register_com_mediatek_perfservice_PerfServiceManager(env);
#if defined (MTK_HDMI_SUPPORT)
register_com_mediatek_hdmi_MtkHdmiManagerService(env);
#endif
// Mediatek AAL support
register_android_server_display_DisplayPowerController(env);
#ifndef MTK_BSP_PACKAGE
register_com_android_internal_app_ShutdownManager(env);
#endif
register_android_server_HelloService(env);//add by eliot_shao
return JNI_VERSION_1_4;
}编译：
android 2.3 和android 6.0版本的JNI位置发生了一点变化。
将com_android_server_HelloService.cpp放入frameworks\base\services\core\jni\
修改: LOGI–>ALOGI
LOGE–>ALOGE
修改onload.cpp 和 Android.mk
编译：mmm frameworks/base/services/
生成system/lib/libandroid_servers.so
