Android-GnssHal层gps.xxx.so查找与加载过程分析

Android-GnssHal层gps.xxx.so查找与加载过程分析

gps.xxx.so不是在系统编译的时候直接prelink的而是在运行阶段由gnss hal service动态查找并加载的;

android.hardware.gnss@1.0-service.rc 会在系统启动时 启动 android.hardware.gnss@1.0-service 然后通过 hw_get_module 获取到对应的module并open以及获取 interface ;

IGnss* HIDL_FETCH_IGnss(const char* /* hal */) {     hw_module_t* module;     IGnss* iface = nullptr;     int err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);     if (err == 0) {         hw_device_t* device;         err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);         if (err == 0) {             iface = new Gnss(reinterpret_cast<gps_device_t*>(device));         } else {             ALOGE("gnssDevice open %s failed: %d", GPS_HARDWARE_MODULE_ID, err);         }     } else {       ALOGE("gnss hw_get_module %s failed: %d", GPS_HARDWARE_MODULE_ID, err);                                  }     return iface; }

hw_get_module 接口的实现在 hardware/libhardware/hardware.c 线面对几个关键步骤进行分析

/**  * 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" }; 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 {         handle = android_load_sphal_library(path, RTLD_NOW);     }     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;     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; } /*  * 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 (access(path, R_OK) == 0)         return 0;     snprintf(path, path_len, "%s/%s.%s.so",              HAL_LIBRARY_PATH2, name, subname);     if (access(path, R_OK) == 0)         return 0; #ifndef __ANDROID_VNDK__     snprintf(path, path_len, "%s/%s.%s.so",              HAL_LIBRARY_PATH1, name, subname);     if (access(path, R_OK) == 0)         return 0; #endif     return -ENOENT; } 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); } int hw_get_module(const char *id, const struct hw_module_t **module) {     return hw_get_module_by_class(id, NULL, module); }

如 hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module); 调用中 GPS_HARDWARE_MODULE_ID 被定义为 "gps", module 为出参, 即找到的module结构体回传给调用者;

hw_get_module 实际是调用 hw_get_module_by_class 并将 id 作为入参传递; 在 hw_get_module_by_class 中会构建一个prop_name即 ro.hardware.%s 其中%s用参数id代替; 这里是 ro.hardware.gps;

如果系统能查找到 ro.hardware.gps property 并且属性值不为空,就会调用 hw_module_exists 查找so的path;     so的格式是 "path/gps.%s.so" 其中%s用查到的属性值代替;     这里的path按照如下定义的path中的3 2 1的顺序查找     #if defined(__LP64__)     #define HAL_LIBRARY_PATH1 "/system/lib64/hw"     #define HAL_LIBRARY_PATH2 "/vendor/lib64/hw"     #define HAL_LIBRARY_PATH3 "/odm/lib64/hw"     #else     #define HAL_LIBRARY_PATH1 "/system/lib/hw"     #define HAL_LIBRARY_PATH2 "/vendor/lib/hw"     #define HAL_LIBRARY_PATH3 "/odm/lib/hw"     #endif     调试时可以使用 getprop 命令获取系统所有的property并确认每个property的值;     如执行命令 # getprop | grep hardware     [ro.hardware]: [xxxv3]     则需要把 gps so 命名为 gps.xxxv3.so 并放到上述定义的 /system/ 或 /vendor 或 /odm 对应的目录下才会被正确加载;     如果 access 成功 即对应的文件存在, 则直接 goto 到标签 found: 即直接执行load加载对应的so;     如果库文件是在 /system 目录下则直接使用dlopen打开,否则使用 android_load_sphal_library 打开; 如果不能查找到 ro.hardware.%s 属性或属性值为空,则循环查找 variant_keys 中的 property;     variant_keys 被定义如下     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"     };     这里 会获取到诸如 版型,平台,架构等;     获取到对应的属性值后会尝试到上述目录下查找 gps.xxx.so 文件并加载; 如果上述尝试都没有成功找到一个对应的 gps so 文件则会尝试最后一个命名规则;     hw_module_exists(path, sizeof(path), name, "default");     即在上述路径查找命名如 gps.default.so 的文件并尝试加载; 否则返回值为2,即 ENOENT: no such file or directory.