高通 sensor 从native到HAL

app注册传感器监听

Android Sensor Framework 的整体架构如下图所示:

前几篇sensor相关的文章介绍了sensor的hal的知识，以press_sensor实时显示气压坐标来分析，app层数据获取的过程，其实实现数据监控非常简单，主要分为下面三个步骤：

• 获取Sensor服务：getSystemService；
• 获取具体Sensor对象：getDefaultSensor；
• 注册数据监听器：registerListener；

SensorService启动

开机后，system server启动时，就会初始化sensor service，也就是说，开机后她一直都在后台运行着，客户端部分，直接connect就行了。至于怎么connect，这一切都被封装到SensorManager里了。

SensorService服务启动后，在随后的第一次被强引用时，其onFirstRef会被调用，紧接着，它会获取我们的SensorDevice实例:

void SensorService::onFirstRef() {
    ALOGD("nuSensorService starting...");
    SensorDevice& dev(SensorDevice::getInstance());

    sHmacGlobalKeyIsValid = initializeHmacKey();

    if (dev.initCheck() == NO_ERROR) {
        sensor_t const* list;
        ssize_t count = dev.getSensorList(&list);
        if (count > 0) {

附上这部分的流程

SensorDevice作为Sensor架构中native的最后一个文件，与Hal层进行通信，故而在SensorDevice的构造方法中，我们就可以看到著名的hw_get_module和sensors_open_1方法了：

SensorDevice::SensorDevice()
    :  mSensorDevice(0),
       mSensorModule(0) {
    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);

    ALOGE_IF(err, "couldn't load %s module (%s)",
            SENSORS_HARDWARE_MODULE_ID, strerror(-err));

    if (mSensorModule) {
        err = sensors_open_1(&mSensorModule->common, &mSensorDevice);

        ALOGE_IF(err, "couldn't open device for module %s (%s)",
                SENSORS_HARDWARE_MODULE_ID, strerror(-err));

        if (mSensorDevice) {
            if (mSensorDevice->common.version == SENSORS_DEVICE_API_VERSION_1_1 ||
                mSensorDevice->common.version == SENSORS_DEVICE_API_VERSION_1_2) {
                ALOGE(">>>> WARNING <<< Upgrade sensor HAL to version 1_3");
            }

            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(
                        reinterpret_cast<struct sensors_poll_device_t *>(mSensorDevice),
                        list[i].handle, 0);
            }
        }
    }
}

其中SENSORS_HARDWARE_MODULE_ID是在hardware/sensors.h中定义的module名字：

/**
 * The id of this module
 */
#define SENSORS_HARDWARE_MODULE_ID "sensors"

而mSensorModule就是我们的sensors_module_t结构体，这些都是在hal层sensors.h中定义的：

/**
 * 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.
 */
struct sensors_module_t {
    struct hw_module_t common;

    /**
     * Enumerate all available sensors. The list is returned in "list".
     * @return number of sensors in the list
     */
    int (*get_sensors_list)(struct sensors_module_t* module,
            struct sensor_t const** list);

    /**
     *  Place the module in a specific mode. The following modes are defined
     *
     *  0 - Normal operation. Default state of the module.
     *  1 - Loopback mode. Data is injected for the supported
     *      sensors by the sensor service in this mode.
     * @return 0 on success
     *         -EINVAL if requested mode is not supported
     *         -EPERM if operation is not allowed
     */
    int (*set_operation_mode)(unsigned int mode);
};

可以看到sensors_module_t结构体扩展了hw_module_t，它里面额外提供了get_sensor_list方法来获取系统支持的sensor列表以及一个模式设置方法。

接下来，我们跟进hw_get_module方法，看看它到底做了什么？

hw_get_module

该函数具体实现在hardware/libhardware/hardware.c中

int hw_get_module(const char *id, const struct hw_module_t **module)
{
    return hw_get_module_by_class(id, NULL, module);
}

int hw_get_module_by_class(const char *class_id, const char *inst,
                           const struct hw_module_t **module)
{
    int i = 0;
    char prop[PATH_MAX] = {0};
    char path[PATH_MAX] = {0};
    char name[PATH_MAX] = {0};
    char prop_name[PATH_MAX] = {0};
 
 
    if (inst)
        snprintf(name, PATH_MAX, "%s.%s", class_id, inst);
    else
        strlcpy(name, class_id, 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.
     */
 
    /* First try a property specific to the class and possibly instance */
    snprintf(prop_name, sizeof(prop_name), "ro.hardware.%s", name);
    if (property_get(prop_name, prop, NULL) > 0) {
        if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
            goto found;
        }
    }
 
    /* Loop through the configuration variants looking for a module */
    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT; i++) {
        if (property_get(variant_keys[i], prop, NULL) == 0) {
            continue;
        }
        if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
            goto found;
        }
    }
 
    /* Nothing found, try the default */
    if (hw_module_exists(path, sizeof(path), name, "default") == 0) {
        goto found;
    }
 
    return -ENOENT;
 
found:
    /* load the module, if this fails, we're doomed, and we should not try
     * to load a different variant. */
    return load(class_id, path, module);
}

我们主要看hw_get_module_by_class，这里传入的参数分别是“sensors”，null，以及我们的mSensorModule结构体。

首先将字符串拷贝给name：

strlcpy(name, class_id, PATH_MAX);

接着拼接prop_name为ro.hardware.name，即prop_name=ro.hardware.sensors

通过property_get方法并没有得到这个值的定义(因为在系统中并没有对其定义)，所以接下来会进入下面的循环：

for (i=0 ; i<HAL_VARIANT_KEYS_COUNT; i++) {
        if (property_get(variant_keys[i], prop, NULL) == 0) {
            continue;
        }
        if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
            goto found;
        }
    }

/**
 * There are a set of variant filename for modules. The form of the filename
 * is "<MODULE_ID>.variant.so" so for the led module the Dream variants 
 * of base "ro.product.board", "ro.board.platform" and "ro.arch" would be:
 *
 * led.trout.so
 * led.msm7k.so
 * led.ARMV6.so
 * led.default.so
 */
 
static const char *variant_keys[] = {
    "ro.hardware",  /* This goes first so that it can pick up a different
                       file on the emulator. */
    "ro.product.board",
    "ro.board.platform",
    "ro.arch"
};

根据上面的解析我门也可以看到，将会分别查找sensors.variant.so，sensors.product.so，sensors.platform.so，以及sensors.default.so，最终我们会在/system/lib/hw/路径下找到sensors.msm8909.so，然后将其通过load方法加载进内存中运行。由此也可知，我分析的是高通8909平台。

小细节：当我们实现了自己的HAL层module，并且写了一个应用程序测试module是否正常工作，那么在编译的时候，下面的参数应该要这样写：

LOCAL_MODULE := moduleName.default

或者

LOCAL_MODULE := moduleName.$(TARGET_BOARD_PLATFORM)

由于上面源码的原因，如果module名字对应不到，你的这个模块将不会被正常的load进去，因而也就无法正常工作了。

接着我们分析load的实现。

static int load(const char *id,
        const char *path,
        const struct hw_module_t **pHmi)
{
    int status = -EINVAL;
    void *handle = NULL;
    struct hw_module_t *hmi = NULL;
 
    /*
     * 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();
        ALOGE("load: module=%s
%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) {
        ALOGE("load: couldn't find symbol %s", sym);
        status = -EINVAL;
        goto done;
    }
 
    /* Check that the id matches */
    if (strcmp(id, hmi->id) != 0) {
        ALOGE("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 {
        ALOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
                id, path, *pHmi, handle);
    }
 
    *pHmi = hmi;
 
    return status;
}

1. 首先通过dlopen打开sensors.xxx.so模块，获得其句柄handle
2. 调用dlsym去获取结构体hw_module_t结构体的地址，注意这里传入的字符串为HAL_MODULE_INFO_SYM_AS_STR，定义在hardware.h头文件中

/**
 * Name of the hal_module_info
 */
#define HAL_MODULE_INFO_SYM         HMI
 
/**
 * Name of the hal_module_info as a string
 */
#define HAL_MODULE_INFO_SYM_AS_STR  "HMI"

这里为什么要去取名字为HMI的地址，我猜想它应该是HAL模块的入口了。

ELF文件格式：

ELF = Executable and Linkable Format，可执行连接格式，是UNIX系统实验室（USL）作为应用程序二进制接口（Application Binary Interface，ABI）而开发和发布的，扩展名为elf。一个ELF头在文件的开始，保存了路线图(road map)，描述了该文件的组织情况。sections保存着object 文件的信息，从连接角度看：包括指令，数据,符号表，重定位信息等等。通过file命令我们可知sensors.xx.so是一个ELF文件格式

tiny.hui@build-server:~$ file sensors.msm8909.so
sensors.msm8909.so: ELF 32-bit LSB shared object, ARM, version 1 (SYSV), dynamically linked (uses shared libs), BuildID[md5/uuid]=0x25812b01ab4700281b41f61327075611, not stripped

因此，通过linux的readelf命令我们可以查看该文件的内部布局及符号表等信息。

tiny.hui@build-server:~$ readelf -s sensors.msm8909.so
 
Symbol table '.dynsym' contains 157 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 00000000     0 FUNC    GLOBAL DEFAULT  UND __cxa_finalize@LIBC (2)
     2: 00000000     0 FUNC    GLOBAL DEFAULT  UND __cxa_atexit@LIBC (2)
     3: 00000000     0 FUNC    GLOBAL DEFAULT  UND __register_atfork@LIBC (2)
     4: 00000000     0 FUNC    GLOBAL DEFAULT  UND pthread_mutex_lock@LIBC (2)
        …………………………// 省略无关信息
    179: 0000c179   120 FUNC    GLOBAL DEFAULT   13 _ZN19NativeSensorManager1
   180: 0000bd21   392 FUNC    GLOBAL DEFAULT   13 _ZN19NativeSensorManager2
   181: 0000a45b   114 FUNC    GLOBAL DEFAULT   13 _ZN24InputEventCircularRe
   182: 000064d9   148 FUNC    GLOBAL DEFAULT   13 _ZN22sensors_poll_context
   183: 0000d889     6 FUNC    GLOBAL DEFAULT   13 _ZN11sensors_XMLC1Ev
   184: 0000663d   156 FUNC    GLOBAL DEFAULT   13 _ZN10SensorBaseC2EPKcS1_P
   185: 000086d5   248 FUNC    GLOBAL DEFAULT   13 _ZN11AccelSensorC1Ev
   186: 000088dd   248 FUNC    GLOBAL DEFAULT   13 _ZN11AccelSensorC2EP13Sen
   187: 00014220     4 OBJECT  GLOBAL DEFAULT   23 _ZN7android9SingletonI11s
   188: 0000a53b    46 FUNC    GLOBAL DEFAULT   13 _ZN18CalibrationManager10
   189: 00007775    56 FUNC    GLOBAL DEFAULT   13 _ZN15ProximitySensorD1Ev
   190: 00014008   136 OBJECT  GLOBAL DEFAULT   22 HMI
   191: 0000721d    26 FUNC    GLOBAL DEFAULT   13 _ZNK11AccelSensor16hasPen
   192: 0000d475    16 FUNC    WEAK   DEFAULT   13 _ZNK7android12SortedVecto
   193: 00006dd9   264 FUNC    GLOBAL DEFAULT   13 _ZN11LightSensorC2EPc
   194: 00006181    48 FUNC    GLOBAL DEFAULT   13 _ZN22sensors_poll_context
   195: 0000d4fd    48 FUNC    GLOBAL DEFAULT   13 _ZN13VirtualSensorD1Ev
   196: 0000aa15    80 FUNC    GLOBAL DEFAULT   13 _ZN18CalibrationManagerD2
   197: 000087cd   272 FUNC    GLOBAL DEFAULT   13 _ZN11AccelSensorC1EPc

由符号表可知，HMI的地址为00014008，拿到函数地址，当然就可以执行对应的代码了。

QualComm Sensor HAL

因此我们接着看sensor_hal层，高通的Sensor实现了自己的HAL，其源码在hardwareqcomsensors路径下，通过Android.mk我们也可以确定他确实是我们前面load方法打开的动态链接库,其编译后会生成sensor.msm8909.so：

ifneq ($(filter msm8960 msm8610 msm8916 msm8909,$(TARGET_BOARD_PLATFORM)),)
# Exclude SSC targets
ifneq ($(TARGET_USES_SSC),true)
# Disable temporarily for compilling error
ifneq ($(BUILD_TINY_ANDROID),true)
LOCAL_PATH := $(call my-dir)

# HAL module implemenation stored in
include $(CLEAR_VARS)

ifeq ($(USE_SENSOR_MULTI_HAL),true)
  LOCAL_MODULE := sensors.native
else
  ifneq ($(filter msm8610,$(TARGET_BOARD_PLATFORM)),)
    LOCAL_MODULE := sensors.$(TARGET_BOARD_PLATFORM)
    LOCAL_CFLAGS := -DTARGET_8610
  else
    ifneq ($(filter msm8916 msm8909,$(TARGET_BOARD_PLATFORM)),)
      LOCAL_MODULE := sensors.$(TARGET_BOARD_PLATFORM)
    else
      LOCAL_MODULE := sensors.msm8960
    endif
  endif

  ifdef TARGET_2ND_ARCH
    LOCAL_MODULE_RELATIVE_PATH := hw
  else
    LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
  endif
endif

LOCAL_MODULE_TAGS := optional

LOCAL_CFLAGS += -DLOG_TAG="Sensors"
ifeq ($(call is-board-platform,msm8960),true)
  LOCAL_CFLAGS += -DTARGET_8930
endif

LOCAL_C_INCLUDES := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ/usr/include
LOCAL_ADDITIONAL_DEPENDENCIES := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ/usr

# Export calibration library needed dependency headers
LOCAL_COPY_HEADERS_TO := sensors/inc
LOCAL_COPY_HEADERS :=   
                CalibrationModule.h 
                sensors_extension.h 
                sensors.h

LOCAL_SRC_FILES :=      
                sensors.cpp                     
                SensorBase.cpp                  
                LightSensor.cpp                 
                ProximitySensor.cpp             
                CompassSensor.cpp               
                Accelerometer.cpp                               
                Gyroscope.cpp                           
                Bmp180.cpp                              
                InputEventReader.cpp 
                CalibrationManager.cpp 
                NativeSensorManager.cpp 
                VirtualSensor.cpp       
                sensors_XML.cpp 
                SignificantMotion.cpp

LOCAL_C_INCLUDES += external/libxml2/include    

ifeq ($(call is-platform-sdk-version-at-least,20),true)
    LOCAL_C_INCLUDES += external/icu/icu4c/source/common
else
    LOCAL_C_INCLUDES += external/icu4c/common
endif

LOCAL_SHARED_LIBRARIES := liblog libcutils libdl libxml2 libutils

include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS)

LOCAL_MODULE := libcalmodule_common
LOCAL_SRC_FILES := 
                   algo/common/common_wrapper.c 
                   algo/common/compass/AKFS_AOC.c 
                   algo/common/compass/AKFS_Device.c 
                   algo/common/compass/AKFS_Direction.c 
                   algo/common/compass/AKFS_VNorm.c

LOCAL_SHARED_LIBRARIES := liblog libcutils
LOCAL_MODULE_TAGS := optional

ifdef TARGET_2ND_ARCH
LOCAL_MODULE_PATH_32 := $(TARGET_OUT_VENDOR)/lib
LOCAL_MODULE_PATH_64 := $(TARGET_OUT_VENDOR)/lib64
else
LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR_SHARED_LIBRARIES)
endif

include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS)

LOCAL_MODULE := calmodule.cfg
LOCAL_MODULE_TAGS := optional
LOCAL_MODULE_CLASS := ETC
LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR_ETC)
LOCAL_SRC_FILES := calmodule.cfg

include $(BUILD_PREBUILT)

endif #BUILD_TINY_ANDROID
endif #TARGET_USES_SSC
endif #TARGET_BOARD_PLATFORM

那么HMI的入口到底定义在这里的那个文件中呢？

功夫不负有心人，在sensors.cpp中，我们终于找到了HMI的入口，即下面的结构体：

static struct hw_module_methods_t sensors_module_methods = {
    .open = sensors_open
};
 
struct sensors_module_t HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .module_api_version = (uint16_t)SENSORS_DEVICE_API_VERSION_1_3,
        .hal_api_version = HARDWARE_HAL_API_VERSION,
        .id = SENSORS_HARDWARE_MODULE_ID,
        .name = "QTI Sensors Module",
        .author = "Qualcomm Technologies, Inc.",
        .methods = &sensors_module_methods,
        .dso = NULL,
        .reserved = {0},
    },
    .get_sensors_list = sensors_get_sensors_list,
    .set_operation_mode = sensors_set_operation_mode
};

HAL_MODULE_INFO_SYM即上文提到的HMI变量，恭喜各位，这里我们就开启了QualComm Sensor HAL的大门。

最后这个hw_module_t的结构体句柄会返回给我们的SensorDevice的构造函数里：

SensorDevice::SensorDevice()
    :  mSensorDevice(0),
       mSensorModule(0)
{
    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);
 
    ALOGE_IF(err, "couldn't load %s module (%s)",
            SENSORS_HARDWARE_MODULE_ID, strerror(-err));
 
    if (mSensorModule) {
        err = sensors_open_1(&mSensorModule->common, &mSensorDevice);

接着，通过sensors_open_1方法将module->common传入，打开我们的sensor驱动。

// hardware/libhardware/include/hardware/sensors.h
static inline int sensors_open_1(const struct hw_module_t* module,
        sensors_poll_device_1_t** device) {
    return module->methods->open(module,
            SENSORS_HARDWARE_POLL, (struct hw_device_t**)device);
}
 
static inline int sensors_close_1(sensors_poll_device_1_t* device) {
    return device->common.close(&device->common);
}

回过头去看看HMI的结构体定义，其中module->common->open被赋值为sensors_module_methods，其只有一个open方法，因此，module->methods->open最终会调用sensors_open方法来打开驱动程序。

到这里native到hal层的逻辑其实已经基本上分析完了。