【HAL】hw_get_module分析：加载HAL层库，获取camx模块接口

1.HAL module implementation

路径：android\vendor\qcom\proprietary\camx\src\core\hal\camxhal3entry.cpp

// 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"

CAMX_VISIBILITY_PUBLIC camera_module_t HAL_MODULE_INFO_SYM =
{
    .common =
    {
        .tag                = HARDWARE_MODULE_TAG,
        .module_api_version = CAMERA_MODULE_API_VERSION_CURRENT,
        .hal_api_version    = HARDWARE_HAL_API_VERSION,
        .id                 = CAMERA_HARDWARE_MODULE_ID,
        .name               = "QTI Camera HAL",
        .author             = "Qualcomm Technologies, Inc.",
        .methods            = &CamX::g_hwModuleMethods
    },
    .get_number_of_cameras  = CamX::get_number_of_cameras,
    .get_camera_info        = CamX::get_camera_info,
    .set_callbacks          = CamX::set_callbacks,
    .get_vendor_tag_ops     = CamX::get_vendor_tag_ops,
    .open_legacy            = CamX::open_legacy,
    .set_torch_mode         = CamX::set_torch_mode,
    .init                   = CamX::init
};

入口结构体名称为HAL_MODULE_INFO_SYM，根据其宏定义即HMI，camx模块被编译为camera.qcom.so，存放于设备路径：/vendor/lib64/hw/camera.qcom.so

2.调用

路径：android\hardware\interfaces\camera\provider\2.4\default\LegacyCameraProviderImpl_2_4.cpp

通过hw_get_module接口获取camera模块入口结构体。

#define CAMERA_HARDWARE_MODULE_ID "camera"

step1

注意：rawModule类型为camera_module_t，被强制转换为hw_module_t类型去获取结构体。原因是camera_module_t的第一个成员变量即为hw_module_t类型，所以地址相同，获取到该成员变量地址即获取整个结构体地址。

bool LegacyCameraProviderImpl_2_4::initialize() {
    camera_module_t *rawModule;
    int err = hw_get_module(CAMERA_HARDWARE_MODULE_ID,
            (const hw_module_t **)&rawModule);
    if (err < 0) {
        ALOGE("Could not load camera HAL module: %d (%s)", err, strerror(-err));
        return true;
    }
    ......
}

step2

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

step3：hw_get_module_by_class

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"
};

1、获取ro.hardware.camera属性，实测为空
2、遍历variant_keys中字符串的属性

获取ro.hardware属性的值为qcom，再调用hw_module_exists判断对应名称（camera.qcom）的so文件是否存在。
3、 Nothing found, try the default

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);		// name为"camera"

    /*
     * 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);	// 获取ro.hardware.camera属性，实测为空
    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);
}

step4：hw_module_exists

遍历各个路径下是否存在camera.qcom.so文件。一般在/vendor/lib64/hw下。

#define HAL_LIBRARY_PATH1 "/system/lib64/hw"
#define HAL_LIBRARY_PATH2 "/vendor/lib64/hw"
#define HAL_LIBRARY_PATH3 "/odm/lib64/hw"

/*
 * Check if a HAL with given name and subname exists, if so return 0, otherwise
 * otherwise return negative.  On success path will contain the path to the HAL.
 */
static int hw_module_exists(char *path, size_t path_len, const char *name,
                            const char *subname)
{
    snprintf(path, path_len, "%s/%s.%s.so",
             HAL_LIBRARY_PATH3, name, subname);
    if (path_in_path(path, HAL_LIBRARY_PATH3) && access(path, R_OK) == 0)
        return 0;

    snprintf(path, path_len, "%s/%s.%s.so",
             HAL_LIBRARY_PATH2, name, subname);
    if (path_in_path(path, HAL_LIBRARY_PATH2) && access(path, R_OK) == 0)
        return 0;

#ifndef __ANDROID_VNDK__
    snprintf(path, path_len, "%s/%s.%s.so",
             HAL_LIBRARY_PATH1, name, subname);
    if (path_in_path(path, HAL_LIBRARY_PATH1) && access(path, R_OK) == 0)
        return 0;
#endif

    return -ENOENT;
}

step5：load

dlopen camera.qcom.so，dlsym获取HAL_MODULE_INFO_SYM符号的地址，即camx模块的入口结构体地址。

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;
#ifdef __ANDROID_VNDK__
    const bool try_system = false;
#else
    const bool try_system = true;
#endif

    /*
     * 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
     */
    if (try_system &&
        strncmp(path, HAL_LIBRARY_PATH1, strlen(HAL_LIBRARY_PATH1)) == 0) {
        /* If the library is in system partition, no need to check
         * sphal namespace. Open it with dlopen.
         */
        handle = dlopen(path, RTLD_NOW);
    } else {
#if defined(__ANDROID_RECOVERY__)
        handle = dlopen(path, RTLD_NOW);
#else
        handle = android_load_sphal_library(path, RTLD_NOW);
#endif
    }
    if (handle == NULL) {
        char const *err_str = dlerror();
        ALOGE("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;	// 即"HMI"
    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) {	// 检查id是否相同即“camera”
        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, hmi, handle);
    }

    *pHmi = hmi;

    return status;
}