前面，带着大家一起写了一个temperature sensor的驱动，已经一个测试tool来测试这个驱动，基本功能已经ok，若还有问题的可以参考前面2篇文章，在这里我们要在HAL层中添加我们的设备，来跟framework中的代码连接起来。
在开始摆代码之前我觉得有必要啰嗦几句，HAL层我个人觉得是个比较重要的东西，虽然这边现在还不是很成熟，还不是很规范，但是google还是做了很大力气针对HAL的。
首先来介绍一下android HAL 层，
Android的硬件抽象层，简单来说，就是对Linux内核驱动程序的封装，向上提供接口，屏蔽低层的实现细节。也就是说，把对硬件的支持分成了两层，一层放在用户空间（User Space），一层放在内核空间（Kernel Space），其中，硬件抽象层运行在用户空间，而Linux内核驱动程序运行在内核空间。
下图为整个android 架构：
这个是google定义的android整个系统的架构，大家可以看到HAL层起了一个承上启下的作用，HAL层主要是针对一些传感器和一些个硬件而存在的，其实也可以绕过HAL层直接使用JNI来实现从驱动到framework这个过程，但是我们这里主要是讲android中的sensor，针对标准的android而言，sensor都是在HAL中添加的，个人理解还是呼应硬件厂商的建议吧，毕竟这部分代码还可以不开源的。
好了，开源不开源什么的，我是不去关心，对我影响不大，我们还是接着看HAL。
Android硬件抽象层，从下到上涉及到了Android系统的硬件驱动层、硬件抽象层、运行时库和应用程序框架层等等，下图描述了硬件抽象层在Android系统中的位置，以及它和其它层的关系：
现在的libhardware 作法，使用了stub的概念。stub 虽然仍是以*.so 檔的形式存在，但HAL 已经将*.so 档隐藏起来了。Stub 向HAL提供操作函数（operations），而runtime 则是向HAL 取得特定模块（stub）的operations，再callback 这些操作函数。
HAL的实现主要在hardware.c和hardware.h文件中。实质也是通过加载*.so 库。从而呼叫*.so 里的符号（symbol）实现。
--------------------------------------------------------------------------------------------------------------------------------------------------------------
到此，都是些理论的东西，实在是不想讲这些条条杠杠的，从小语文就不好的我，最讨厌的就是这些理论的东西了，实践才是真理呢。。。
好了接下来轮到我们的sensor的HAL层了，这里先列出来主要用到的代码：
。。。。。。
讲漏了，这边sensor的HAL层代码我参考的是freescale的BSP，因为个人感觉比较容易懂，哈哈。
先给
下载链接，不然大家看不到完整的代码。
http://download.csdn.net/detail/zhangjie201412/4039312
代码目录如下：
sensor/
├──AccelSensor.cpp
├──AccelSensor.h
├──Android.mk
├──InputEventReader.cpp
├──InputEventReader.h
├──LightSensor.cpp
├──LightSensor.h
├──SensorBase.cpp
├──SensorBase.h
├──sensors.cpp
├──sensors.h
├──TemperatureSensor.cpp
└──TemperatureSensor.h
这里我们要修改以及添加的是三个文件：
sensor.cpp TemperatureSensor.cpp TemperatureSensor.h
好了，接下来就带大家分析下android sensor的HAL层！！！
先看一下/hardware/libhareware/hardware.c和/hardware/libhardware/include/hardware/hardware.h
这2个文件是android hal层最重要的两个文件，其中定义了hal层主要要实现的3个结构体，
struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;
/**
* Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
* and the fields of this data structure must begin with hw_module_t
* followed by module specific information.
*/
typedef struct hw_module_t {
/** tag must be initialized to HARDWARE_MODULE_TAG */
uint32_t tag;
/** major version number for the module */
uint16_t version_major;
/** minor version number of the module */
uint16_t version_minor;
/** Identifier of module */
const char *id;
/** Name of this module */
const char *name;
/** Author/owner/implementor of the module */
const char *author;
/** Modules methods */
struct hw_module_methods_t* methods;
/** module's dso */
void* dso;
/** padding to 128 bytes, reserved for future use */
uint32_t reserved[32-7];
} hw_module_t;
typedef struct hw_module_methods_t {
/** Open a specific device */
int (*open)(const struct hw_module_t* module, const char* id,
struct hw_device_t** device);
} hw_module_methods_t;
/**
* Every device data structure must begin with hw_device_t
* followed by module specific public methods and attributes.
*/
typedef struct hw_device_t {
/** tag must be initialized to HARDWARE_DEVICE_TAG */
uint32_t tag;
/** version number for hw_device_t */
uint32_t version;
/** reference to the module this device belongs to */
struct hw_module_t* module;
/** padding reserved for future use */
uint32_t reserved[12];
/** Close this device */
int (*close)(struct hw_device_t* device);
} hw_device_t;
struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;
/**
* Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
* and the fields of this data structure must begin with hw_module_t
* followed by module specific information.
*/
typedef struct hw_module_t {
/** tag must be initialized to HARDWARE_MODULE_TAG */
uint32_t tag;
/** major version number for the module */
uint16_t version_major;
/** minor version number of the module */
uint16_t version_minor;
/** Identifier of module */
const char *id;
/** Name of this module */
const char *name;
/** Author/owner/implementor of the module */
const char *author;
/** Modules methods */
struct hw_module_methods_t* methods;
/** module's dso */
void* dso;
/** padding to 128 bytes, reserved for future use */
uint32_t reserved[32-7];
} hw_module_t;
typedef struct hw_module_methods_t {
/** Open a specific device */
int (*open)(const struct hw_module_t* module, const char* id,
struct hw_device_t** device);
} hw_module_methods_t;
/**
* Every device data structure must begin with hw_device_t
* followed by module specific public methods and attributes.
*/
typedef struct hw_device_t {
/** tag must be initialized to HARDWARE_DEVICE_TAG */
uint32_t tag;
/** version number for hw_device_t */
uint32_t version;
/** reference to the module this device belongs to */
struct hw_module_t* module;
/** padding reserved for future use */
uint32_t reserved[12];
/** Close this device */
int (*close)(struct hw_device_t* device);
} hw_device_t;
其实标准的android hal就是实现这3个结构体，然后设置一些回调函数，最后把数据poll到framework中。
好，接下来看下sensor中是怎么封装的：
在/hardware/libhardware/include/hardware/sensors.h 中定义了几个结构体，其中都包含了上面的3个结构体，所以我们sensor module只需要去实现sensor.h中的这几个就OK了。
下面提一下如何添加我们的temperature sensor，首先是hardware/libhardware/modules/sensor/sensors.cpp 中sensor list中添加我们的sensor的信息，
/* The SENSORS Module */
static const struct sensor_t sSensorList[] = {
{ "Analog Devices ADXL345/6 3-axis Accelerometer",
"ADI",
1, SENSORS_ACCELERATION_HANDLE,
SENSOR_TYPE_ACCELEROMETER, RANGE_A, CONVERT_A, 0.145f, 200, { } }, //20000
{ "Android Light sensor",
"Android",
1, SENSORS_LIGHT_HANDLE,
SENSOR_TYPE_LIGHT, 16000.0f, 1.0f, 0.35f, 0, { } },
//++++++add by Jay for temperature sensor
{ "Android Temperature Sensor",
"Android",
1, SENSORS_TEMPERATURE_HANDLE,
SENSOR_TYPE_TEMPERATURE, 100.0f, 1.0f, 1.0f,0, { }},
//-----------
};
/* The SENSORS Module */
static const struct sensor_t sSensorList[] = {
{ "Analog Devices ADXL345/6 3-axis Accelerometer",
"ADI",
1, SENSORS_ACCELERATION_HANDLE,
SENSOR_TYPE_ACCELEROMETER, RANGE_A, CONVERT_A, 0.145f, 200, { } }, //20000
{ "Android Light sensor",
"Android",
1, SENSORS_LIGHT_HANDLE,
SENSOR_TYPE_LIGHT, 16000.0f, 1.0f, 0.35f, 0, { } },
//++++++add by Jay for temperature sensor
{ "Android Temperature Sensor",
"Android",
1, SENSORS_TEMPERATURE_HANDLE,
SENSOR_TYPE_TEMPERATURE, 100.0f, 1.0f, 1.0f,0, { }},
//-----------
};这里面的Android Temperature Sensor就是我们自己添加的sensor，然后我们去实现我们的temperature sensor的功能，也就是填充一些结构体和实现一些回调函数，这里我挑重要的讲。
int TemperatureSensor::readEvents(sensors_event_t* data, int count)
{
if(count<1)
return -EINVAL;
if(mHasPendingEvent){
mHasPendingEvent = false;
mPendingEvent.timestamp = getTimestamp();
*data = mPendingEvent;
return mEnabled ? 1:0;
}
ssize_t n = mInputReader.fill(data_fd);
if(n<0)
return n;
int numEventReceived = 0;
input_event const* event;
DEBUG("count: %d\n",count);
while(count && mInputReader.readEvent(&event)){
int fd=open("/dev/input/event1", O_RDONLY);
if(fd<0){
DEBUG("readEvents: open event2 failed...\n");
return fd;
}
int ret=read(fd,&event,sizeof(event));
if(ret<sizeof(event)){
DEBUG("readEvent read failed....\n");
return ret;
}
close(fd);
int type=event->type;
if(type == EV_ABS){
DEBUG("Current Temp: %d\n",event->value);
mPendingEvent.temperature = (float)(event->value);
}else if(type==EV_SYN){
mPendingEvent.timestamp = timevalToNano(event->time);
if(/*mEnabled &&*/ (mPendingEvent.temperature != mPreviousTemperature)){
*data++ = mPendingEvent;
count--;
numEventReceived++;
mPreviousTemperature = mPendingEvent.temperature;
DEBUG("Current Temp: %d\n",(int)mPendingEvent.temperature);
}
}else
DEBUG("temperature : unknow event...\n");
mInputReader.next();
}
return numEventReceived;
}
int TemperatureSensor::readEvents(sensors_event_t* data, int count)
{
if(count<1)
return -EINVAL;
if(mHasPendingEvent){
mHasPendingEvent = false;
mPendingEvent.timestamp = getTimestamp();
*data = mPendingEvent;
return mEnabled ? 1:0;
}
ssize_t n = mInputReader.fill(data_fd);
if(n<0)
return n;
int numEventReceived = 0;
input_event const* event;
DEBUG("count: %d\n",count);
while(count && mInputReader.readEvent(&event)){
int fd=open("/dev/input/event1", O_RDONLY);
if(fd<0){
DEBUG("readEvents: open event2 failed...\n");
return fd;
}
int ret=read(fd,&event,sizeof(event));
if(ret<sizeof(event)){
DEBUG("readEvent read failed....\n");
return ret;
}
close(fd);
int type=event->type;
if(type == EV_ABS){
DEBUG("Current Temp: %d\n",event->value);
mPendingEvent.temperature = (float)(event->value);
}else if(type==EV_SYN){
mPendingEvent.timestamp = timevalToNano(event->time);
if(/*mEnabled &&*/ (mPendingEvent.temperature != mPreviousTemperature)){
*data++ = mPendingEvent;
count--;
numEventReceived++;
mPreviousTemperature = mPendingEvent.temperature;
DEBUG("Current Temp: %d\n",(int)mPendingEvent.temperature);
}
}else
DEBUG("temperature : unknow event...\n");
mInputReader.next();
}
return numEventReceived;
}大家看了Temperature.cpp就应该知道我这里实现HAL层poll数据最主要的就是上面这个函数，这边其实就是linux的应用层的写法，open input 节点，然后read data，在poll给framework层。
这里我要提醒大家，如果对自己不够有信心的话第一次写hal层代码的时候最好多加点debug message，因为在hal层的调试比较麻烦，出现的错误会直接导致系统不断重启，不会告诉你错哪，所以，最好自己加debug message来调试。
代码方面大家可以看下Temperature.h和sensor.cpp这两个文件里面要实现的一些类和结构体，按照规范写好回调函数就ok了，大家自行分析绰绰有余。
还有就是这里的makefile，会把module编译成sensor.goldfish.so，给framework调用，ok来讲一下framework是如何调用HAL层里面的API的，
大家可以看下android
源码下面的frameworks/base/services/sensorservice/SensorDevice.cpp
SensorDevice::SensorDevice()
: mSensorDevice(0),
mSensorModule(0)
{
status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
(hw_module_t const**)&mSensorModule);
LOGE_IF(err, "couldn't load %s module (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorModule) {
err = sensors_open(&mSensorModule->common, &mSensorDevice);
LOGE_IF(err, "couldn't open device for module %s (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorDevice) {
sensor_t const* list;
ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);
mActivationCount.setCapacity(count);
Info model;
for (size_t i=0 ; i<size_t(count) ; i++) {
mActivationCount.add(list[i].handle, model);
mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
}
}
}
}
SensorDevice::SensorDevice()
: mSensorDevice(0),
mSensorModule(0)
{
status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
(hw_module_t const**)&mSensorModule);
LOGE_IF(err, "couldn't load %s module (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorModule) {
err = sensors_open(&mSensorModule->common, &mSensorDevice);
LOGE_IF(err, "couldn't open device for module %s (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorDevice) {
sensor_t const* list;
ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);
mActivationCount.setCapacity(count);
Info model;
for (size_t i=0 ; i<size_t(count) ; i++) {
mActivationCount.add(list[i].handle, model);
mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
}
}
}
}
这里调用了status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
(hw_module_t const**)&mSensorModule);
status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
(hw_module_t const**)&mSensorModule);
这个函数在哪呢？在这：
hardware/libhardware/hardware.c里的
int hw_get_module(const char *id, const struct hw_module_t **module)
{
int status;
int i;
const struct hw_module_t *hmi = NULL;
char prop[PATH_MAX];
char path[PATH_MAX];
/*
* Here we rely on the fact that calling dlopen multiple times on
* the same .so will simply increment a refcount (and not load
* a new copy of the library).
* We also assume that dlopen() is thread-safe.
*/
/* Loop through the configuration variants looking for a module */
for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
if (i < HAL_VARIANT_KEYS_COUNT) {
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH1, id, prop);
if (access(path, R_OK) == 0) break;
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH2, id, prop);
if (access(path, R_OK) == 0) break;
} else {
snprintf(path, sizeof(path), "%s/%s.default.so",
HAL_LIBRARY_PATH1, id);
if (access(path, R_OK) == 0) break;
}
}
status = -ENOENT;
if (i < HAL_VARIANT_KEYS_COUNT+1) {
/* load the module, if this fails, we're doomed, and we should not try
* to load a different variant. */
status = load(id, path, module);
}
return status;
}
int hw_get_module(const char *id, const struct hw_module_t **module)
{
int status;
int i;
const struct hw_module_t *hmi = NULL;
char prop[PATH_MAX];
char path[PATH_MAX];
/*
* Here we rely on the fact that calling dlopen multiple times on
* the same .so will simply increment a refcount (and not load
* a new copy of the library).
* We also assume that dlopen() is thread-safe.
*/
/* Loop through the configuration variants looking for a module */
for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
if (i < HAL_VARIANT_KEYS_COUNT) {
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH1, id, prop);
if (access(path, R_OK) == 0) break;
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH2, id, prop);
if (access(path, R_OK) == 0) break;
} else {
snprintf(path, sizeof(path), "%s/%s.default.so",
HAL_LIBRARY_PATH1, id);
if (access(path, R_OK) == 0) break;
}
}
status = -ENOENT;
if (i < HAL_VARIANT_KEYS_COUNT+1) {
/* load the module, if this fails, we're doomed, and we should not try
* to load a different variant. */
status = load(id, path, module);
}
return status;
}
这里首先把要get的module的名字传进去，然后找到sensor.goldfish.so，但是怎么去加载这个binary呢？
看下这里的load函数：
/**
* Load the file defined by the variant and if successful
* return the dlopen handle and the hmi.
* @return 0 = success, !0 = failure.
*/
static int load(const char *id,
const char *path,
const struct hw_module_t **pHmi)
{
int status;
void *handle;
struct hw_module_t *hmi;
/*
* load the symbols resolving undefined symbols before
* dlopen returns. Since RTLD_GLOBAL is not or'd in with
* RTLD_NOW the external symbols will not be global
*/
handle = dlopen(path, RTLD_NOW);
if (handle == NULL) {
char const *err_str = dlerror();
LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
status = -EINVAL;
goto done;
}
/* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym);
if (hmi == NULL) {
LOGE("load: couldn't find symbol %s", sym);
status = -EINVAL;
goto done;
}
/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
status = -EINVAL;
goto done;
}
hmi->dso = handle;
/* success */
status = 0;
done:
if (status != 0) {
hmi = NULL;
if (handle != NULL) {
dlclose(handle);
handle = NULL;
}
} else {
LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
id, path, *pHmi, handle);
}
*pHmi = hmi;
return status;
}
/**
* Load the file defined by the variant and if successful
* return the dlopen handle and the hmi.
* @return 0 = success, !0 = failure.
*/
static int load(const char *id,
const char *path,
const struct hw_module_t **pHmi)
{
int status;
void *handle;
struct hw_module_t *hmi;
/*
* load the symbols resolving undefined symbols before
* dlopen returns. Since RTLD_GLOBAL is not or'd in with
* RTLD_NOW the external symbols will not be global
*/
handle = dlopen(path, RTLD_NOW);
if (handle == NULL) {
char const *err_str = dlerror();
LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
status = -EINVAL;
goto done;
}
/* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym);
if (hmi == NULL) {
LOGE("load: couldn't find symbol %s", sym);
status = -EINVAL;
goto done;
}
/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
status = -EINVAL;
goto done;
}
hmi->dso = handle;
/* success */
status = 0;
done:
if (status != 0) {
hmi = NULL;
if (handle != NULL) {
dlclose(handle);
handle = NULL;
}
} else {
LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
id, path, *pHmi, handle);
}
*pHmi = hmi;
return status;
}
handle = dlopen(path, RTLD_NOW)；这个函数是用来打开找到的sensor.goldfish.so这个动态库的，然后找到这个库里的一些回调函数，怎么找呢？
handle = dlopen(path, RTLD_NOW)；这个函数是用来打开找到的sensor.goldfish.so这个动态库的，然后找到这个库里的一些回调函数，怎么找呢？看下这句话：
看下这句话：<pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); "><pre name="code" class="cpp"> /* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
<pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); "><pre name="code" class="cpp"> /* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
HAL_MODULE_INFO_SYM_AS_STR;是一个宏，被定义在hardware.h中：
HAL_MODULE_INFO_SYM_AS_STR;是一个宏，被定义在hardware.h中：<pre name="code" class="cpp">#define HAL_MODULE_INFO_SYM_AS_STR "HMI"
<pre name="code" class="cpp">#define HAL_MODULE_INFO_SYM_AS_STR "HMI"好了，就是找HMI这个字串，我们可以用readelf命令查看下sensor.glodfish.so里面的symbol：
<pre name="code" class="cpp">root@jay:/home/jay/android/android2.3.3# readelf -s out/target/product/generic/system/lib/hw/sensors.goldfish.so
Symbol table '.dynsym' contains 118 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr0
2: 00001a29 44 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
3: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_f2iz
4: 00001a5d 364 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
5: 00000000 0 FUNC GLOBAL DEFAULT UND poll
6: 00000000 0 FUNC GLOBAL DEFAULT UND __errno
7: 00000000 0 FUNC GLOBAL DEFAULT UND strerror
8: 00000000 0 FUNC GLOBAL DEFAULT UND __android_log_print
9: 00000000 0 FUNC GLOBAL DEFAULT UND read
10: 00001bd1 120 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
11: 00000000 0 FUNC GLOBAL DEFAULT UND write
12: 00001c51 42 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
13: 00000000 0 FUNC GLOBAL DEFAULT UND close
14: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv
15: 00001c95 42 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
16: 00001cc1 216 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
17: 00000000 0 FUNC GLOBAL DEFAULT UND _Znwj
18: 00002455 124 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorC1Ev
19: 00002af1 288 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorC1Ev
20: 00002fd5 108 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorC1E
21: 00000000 0 FUNC GLOBAL DEFAULT UND pipe
22: 00000000 0 FUNC GLOBAL DEFAULT UND fcntl
23: 00000000 0 FUNC GLOBAL DEFAULT UND memset
24: 00001ded 216 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
25: 0000432c 132 OBJECT GLOBAL DEFAULT 16 HMI
26: 00001ec5 24 FUNC GLOBAL DEFAULT 7 _ZNK10SensorBase5getFdEv
27: 00001edd 4 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase8setDelayE
28: 00001ee1 4 FUNC GLOBAL DEFAULT 7 _ZNK10SensorBase16hasPend
29: 00001ee5 32 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase12close_de
30: 00001f05 60 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD1Ev
31: 000040e8 36 OBJECT GLOBAL DEFAULT 13 _ZTV10SensorBase
32: 00001f41 60 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD2Ev
33: 00001f7d 312 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase9openInput
34: 00000000 0 FUNC GLOBAL DEFAULT UND opendir
35: 00000000 0 FUNC GLOBAL DEFAULT UND strcpy
36: 00000000 0 FUNC GLOBAL DEFAULT UND strlen
37: 00000000 0 FUNC GLOBAL DEFAULT UND open
38: 00000000 0 FUNC GLOBAL DEFAULT UND ioctl
39: 00000000 0 FUNC GLOBAL DEFAULT UND strcmp
40: 00000000 0 FUNC GLOBAL DEFAULT UND readdir
41: 00000000 0 FUNC GLOBAL DEFAULT UND closedir
42: 00000000 0 FUNC GLOBAL DEFAULT UND __stack_chk_fail
43: 00000000 0 OBJECT GLOBAL DEFAULT UND __stack_chk_guard
44: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr1
45: 000020b5 68 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseC1EPKcS1_
46: 000020f9 68 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseC2EPKcS1_
47: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_lmul
48: 00002141 56 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase12getTimes
49: 00000000 0 FUNC GLOBAL DEFAULT UND clock_gettime
50: 00002179 80 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase11open_dev
51: 000021c9 18 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD0Ev
52: 00000000 0 FUNC GLOBAL DEFAULT UND __cxa_pure_virtual
53: 000021dd 4 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor8setDelay
54: 000021e1 24 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor6enableEi
55: 000021f9 12 FUNC GLOBAL DEFAULT 7 _ZNK11LightSensor16hasPen
56: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_i2f
57: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_fcmpeq
58: 00002209 432 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor10readEve
59: 00000000 0 FUNC GLOBAL DEFAULT UND memcpy
60: 000030dd 96 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
61: 000030c5 24 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
62: 000030ad 22 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
63: 000023b9 68 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD1Ev
64: 0000313d 18 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
65: 00004110 36 OBJECT GLOBAL DEFAULT 13 _ZTV11LightSensor
66: 000023fd 18 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD0Ev
67: 00002411 68 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD2Ev
68: 00003165 30 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
69: 000024d1 124 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorC2Ev
70: 0000254d 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor6enableEi
71: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_fmul
72: 0000257d 120 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor12process
73: 000025f9 308 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor10readEve
74: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_ldivmod
75: 00002731 216 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor8setDelay
76: 00000000 0 FUNC GLOBAL DEFAULT UND fopen
77: 00000000 0 FUNC GLOBAL DEFAULT UND snprintf
78: 00000000 0 FUNC GLOBAL DEFAULT UND fwrite
79: 00000000 0 FUNC GLOBAL DEFAULT UND fclose
80: 00002809 628 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor11getPoll
81: 00000000 0 FUNC GLOBAL DEFAULT UND strncmp
82: 00000000 0 FUNC GLOBAL DEFAULT UND strcat
83: 00000000 0 FUNC GLOBAL DEFAULT UND fread
84: 00000000 0 FUNC GLOBAL DEFAULT UND strtol
85: 00002a7d 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD1Ev
86: 00004138 36 OBJECT GLOBAL DEFAULT 13 _ZTV11AccelSensor
87: 00002aad 18 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD0Ev
88: 00002ac1 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD2Ev
89: 00002c11 288 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorC2Ev
90: 00002d31 4 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor8se
91: 00002d35 24 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor6en
92: 00002d4d 12 FUNC GLOBAL DEFAULT 7 _ZNK17TemperatureSensor16
93: 00002d59 488 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor10r
94: 00002f41 64 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD1E
95: 00004160 36 OBJECT GLOBAL DEFAULT 13 _ZTV17TemperatureSensor
96: 00002f81 18 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD0E
97: 00002f95 64 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD2E
98: 00003041 108 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorC2E
99: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdaPv
100: 00003151 18 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
101: 00000000 0 FUNC GLOBAL DEFAULT UND _Znaj
102: 00003185 30 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
103: 00000000 0 FUNC GLOBAL DEFAULT UND __cxa_finalize
104: 000043c0 0 NOTYPE GLOBAL DEFAULT 17 __dso_handle
105: 00004000 0 NOTYPE GLOBAL DEFAULT 11 __INIT_ARRAY__
106: 00004008 0 NOTYPE GLOBAL DEFAULT 12 __FINI_ARRAY__
107: 000035dc 0 NOTYPE GLOBAL DEFAULT ABS __exidx_start
108: 0000371c 0 NOTYPE GLOBAL DEFAULT ABS __exidx_end
109: 0000432c 0 NOTYPE GLOBAL DEFAULT 16 __data_start
110: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS _edata
111: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
112: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start__
113: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS _bss_end__
114: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS __bss_end__
115: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS __end__
116: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS _end
117: 00080000 0 NOTYPE GLOBAL DEFAULT ABS _stack
<pre name="code" class="cpp">root@jay:/home/jay/android/android2.3.3# readelf -s out/target/product/generic/system/lib/hw/sensors.goldfish.so
Symbol table '.dynsym' contains 118 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr0
2: 00001a29 44 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
3: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_f2iz
4: 00001a5d 364 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
5: 00000000 0 FUNC GLOBAL DEFAULT UND poll
6: 00000000 0 FUNC GLOBAL DEFAULT UND __errno
7: 00000000 0 FUNC GLOBAL DEFAULT UND strerror
8: 00000000 0 FUNC GLOBAL DEFAULT UND __android_log_print
9: 00000000 0 FUNC GLOBAL DEFAULT UND read
10: 00001bd1 120 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
11: 00000000 0 FUNC GLOBAL DEFAULT UND write
12: 00001c51 42 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
13: 00000000 0 FUNC GLOBAL DEFAULT UND close
14: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv
15: 00001c95 42 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
16: 00001cc1 216 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
17: 00000000 0 FUNC GLOBAL DEFAULT UND _Znwj
18: 00002455 124 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorC1Ev
19: 00002af1 288 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorC1Ev
20: 00002fd5 108 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorC1E
21: 00000000 0 FUNC GLOBAL DEFAULT UND pipe
22: 00000000 0 FUNC GLOBAL DEFAULT UND fcntl
23: 00000000 0 FUNC GLOBAL DEFAULT UND memset
24: 00001ded 216 FUNC GLOBAL DEFAULT 7 _ZN22sensors_poll_context
25: 0000432c 132 OBJECT GLOBAL DEFAULT 16 HMI
26: 00001ec5 24 FUNC GLOBAL DEFAULT 7 _ZNK10SensorBase5getFdEv
27: 00001edd 4 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase8setDelayE
28: 00001ee1 4 FUNC GLOBAL DEFAULT 7 _ZNK10SensorBase16hasPend
29: 00001ee5 32 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase12close_de
30: 00001f05 60 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD1Ev
31: 000040e8 36 OBJECT GLOBAL DEFAULT 13 _ZTV10SensorBase
32: 00001f41 60 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD2Ev
33: 00001f7d 312 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase9openInput
34: 00000000 0 FUNC GLOBAL DEFAULT UND opendir
35: 00000000 0 FUNC GLOBAL DEFAULT UND strcpy
36: 00000000 0 FUNC GLOBAL DEFAULT UND strlen
37: 00000000 0 FUNC GLOBAL DEFAULT UND open
38: 00000000 0 FUNC GLOBAL DEFAULT UND ioctl
39: 00000000 0 FUNC GLOBAL DEFAULT UND strcmp
40: 00000000 0 FUNC GLOBAL DEFAULT UND readdir
41: 00000000 0 FUNC GLOBAL DEFAULT UND closedir
42: 00000000 0 FUNC GLOBAL DEFAULT UND __stack_chk_fail
43: 00000000 0 OBJECT GLOBAL DEFAULT UND __stack_chk_guard
44: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_unwind_cpp_pr1
45: 000020b5 68 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseC1EPKcS1_
46: 000020f9 68 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseC2EPKcS1_
47: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_lmul
48: 00002141 56 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase12getTimes
49: 00000000 0 FUNC GLOBAL DEFAULT UND clock_gettime
50: 00002179 80 FUNC GLOBAL DEFAULT 7 _ZN10SensorBase11open_dev
51: 000021c9 18 FUNC GLOBAL DEFAULT 7 _ZN10SensorBaseD0Ev
52: 00000000 0 FUNC GLOBAL DEFAULT UND __cxa_pure_virtual
53: 000021dd 4 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor8setDelay
54: 000021e1 24 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor6enableEi
55: 000021f9 12 FUNC GLOBAL DEFAULT 7 _ZNK11LightSensor16hasPen
56: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_i2f
57: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_fcmpeq
58: 00002209 432 FUNC GLOBAL DEFAULT 7 _ZN11LightSensor10readEve
59: 00000000 0 FUNC GLOBAL DEFAULT UND memcpy
60: 000030dd 96 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
61: 000030c5 24 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
62: 000030ad 22 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
63: 000023b9 68 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD1Ev
64: 0000313d 18 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
65: 00004110 36 OBJECT GLOBAL DEFAULT 13 _ZTV11LightSensor
66: 000023fd 18 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD0Ev
67: 00002411 68 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorD2Ev
68: 00003165 30 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
69: 000024d1 124 FUNC GLOBAL DEFAULT 7 _ZN11LightSensorC2Ev
70: 0000254d 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor6enableEi
71: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_fmul
72: 0000257d 120 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor12process
73: 000025f9 308 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor10readEve
74: 00000000 0 FUNC GLOBAL DEFAULT UND __aeabi_ldivmod
75: 00002731 216 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor8setDelay
76: 00000000 0 FUNC GLOBAL DEFAULT UND fopen
77: 00000000 0 FUNC GLOBAL DEFAULT UND snprintf
78: 00000000 0 FUNC GLOBAL DEFAULT UND fwrite
79: 00000000 0 FUNC GLOBAL DEFAULT UND fclose
80: 00002809 628 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensor11getPoll
81: 00000000 0 FUNC GLOBAL DEFAULT UND strncmp
82: 00000000 0 FUNC GLOBAL DEFAULT UND strcat
83: 00000000 0 FUNC GLOBAL DEFAULT UND fread
84: 00000000 0 FUNC GLOBAL DEFAULT UND strtol
85: 00002a7d 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD1Ev
86: 00004138 36 OBJECT GLOBAL DEFAULT 13 _ZTV11AccelSensor
87: 00002aad 18 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD0Ev
88: 00002ac1 48 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorD2Ev
89: 00002c11 288 FUNC GLOBAL DEFAULT 7 _ZN11AccelSensorC2Ev
90: 00002d31 4 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor8se
91: 00002d35 24 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor6en
92: 00002d4d 12 FUNC GLOBAL DEFAULT 7 _ZNK17TemperatureSensor16
93: 00002d59 488 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensor10r
94: 00002f41 64 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD1E
95: 00004160 36 OBJECT GLOBAL DEFAULT 13 _ZTV17TemperatureSensor
96: 00002f81 18 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD0E
97: 00002f95 64 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorD2E
98: 00003041 108 FUNC GLOBAL DEFAULT 7 _ZN17TemperatureSensorC2E
99: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdaPv
100: 00003151 18 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
101: 00000000 0 FUNC GLOBAL DEFAULT UND _Znaj
102: 00003185 30 FUNC GLOBAL DEFAULT 7 _ZN24InputEventCircularRe
103: 00000000 0 FUNC GLOBAL DEFAULT UND __cxa_finalize
104: 000043c0 0 NOTYPE GLOBAL DEFAULT 17 __dso_handle
105: 00004000 0 NOTYPE GLOBAL DEFAULT 11 __INIT_ARRAY__
106: 00004008 0 NOTYPE GLOBAL DEFAULT 12 __FINI_ARRAY__
107: 000035dc 0 NOTYPE GLOBAL DEFAULT ABS __exidx_start
108: 0000371c 0 NOTYPE GLOBAL DEFAULT ABS __exidx_end
109: 0000432c 0 NOTYPE GLOBAL DEFAULT 16 __data_start
110: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS _edata
111: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
112: 000043b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start__
113: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS _bss_end__
114: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS __bss_end__
115: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS __end__
116: 000043d0 0 NOTYPE GLOBAL DEFAULT ABS _end
117: 00080000 0 NOTYPE GLOBAL DEFAULT ABS _stack
大家可以看到这里的第25行，OK 找到了，这里找到了这个动态库的地址，然后就可以一次找到这个动态库中的函数，最终可以被调用。
结束语：
这里我只是大致分析了一下这个流程，对于代码是如何编写的，大家可以参考我提供的下载，其实android hal层就是填充一些“规则”。
这里我只是大致分析了一下这个流程，对于代码是如何编写的，大家可以参考我提供的下载，其实android hal层就是填充一些“规则”。下面一节我们来编写一个测试apk来抓我们的温度，之后再来分析framework层，因为到这里我们sensor的移植就结束了，framework层中android已经帮我们把api都写好了，也就是说sensor是android的标准api，我们不需要自己去搭建。
摘自 zhangjie201412的专栏
