多个 Binder 域

android12-release

Binder系列1-Binder Driver
Binder系列2-ServiceManager
Binder系列3-framework层

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1. Binder域：binder,hwbinder,vndbinder

都是Binder IPC，查看 Binder系列1-Binder Driver binder_init() -> init_binder_device(device_name) 注册misc设备节点
对应设备节点：/dev/binder、/dev/hwbinder、/dev/vndbinder

drivers/android/binder.c
kernel/configs/android-base.config
char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
CONFIG_ANDROID_BINDER_DEVICES=binder,hwbinder,vndbinder

2. init.rc文件启动ServiceManager

上边是kernel底层misc设备节点添加

2.1 /dev/binder 框架/应用进程之间的 IPC，使用 AIDL 接口

Binder系列2-ServiceManager

frameworks/native/cmds/servicemanager/servicemanager.rc

• 进程名：servicemanager
• bin文件：/system/bin/servicemanager
• 对应启动入口：frameworks/native/cmds/servicemanager/main.cpp

2.2 /dev/hwbinder 框架/供应商进程之间的 IPC，使用 HIDL 接口；供应商进程之间的 IPC，使用 HIDL 接口

system/hwservicemanager/hwservicemanager.rc

• 进程名：hwservicemanager
• bin文件：/system/bin/hwservicemanager
• 对应启动入口：system/hwservicemanager/service.cpp

2.3 /dev/vndbinder 供应商/供应商进程之间的 IPC，使用 AIDL 接口

与/dev/binder是同一入口，通过rc文件参数区分const char* driver = argc == 2 ? argv[1] : "/dev/binder";
/dev/vndbinder是两个参数service vndservicemanager /vendor/bin/vndservicemanager /dev/vndbinder

frameworks/native/cmds/servicemanager/vndservicemanager.rc

• 进程名：vndservicemanager
• bin文件：/vendor/bin/vndservicemanager
• 对应启动入口：frameworks/native/cmds/servicemanager/main.cpp

3. defaultServiceManager获取

• /dev/binder获取方法defaultServiceManager()，如mediaserver.rc启动通过binder/IServiceManager.h中defaultServiceManager()（frameworks/native/libs/binder/IServiceManager.cpp）

frameworks/av/media/mediaserver/mediaserver.rc
frameworks/av/media/mediaserver/main_mediaserver.cpp
frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp

#include 
#include 
#include 
#include 

void MediaPlayerService::instantiate() {
    defaultServiceManager()->addService(
            String16("media.player"), new MediaPlayerService());
}
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• /dev/hwbinder获取方法defaultServiceManager()（system/libhidl/transport/ServiceManagement.cpp）

sp<IServiceManager1_0> defaultServiceManager() {
    return defaultServiceManager1_2();
}
sp<IServiceManager1_1> defaultServiceManager1_1() {
    return defaultServiceManager1_2();
}
sp<IServiceManager1_2> defaultServiceManager1_2() {
    using android::hidl::manager::V1_2::BnHwServiceManager;
    using android::hidl::manager::V1_2::BpHwServiceManager;

    static std::mutex& gDefaultServiceManagerLock = *new std::mutex;
    static sp<IServiceManager1_2>& gDefaultServiceManager = *new sp<IServiceManager1_2>;

    {
        std::lock_guard<std::mutex> _l(gDefaultServiceManagerLock);
        if (gDefaultServiceManager != nullptr) {
            return gDefaultServiceManager;
        }

        if (access("/dev/hwbinder", F_OK|R_OK|W_OK) != 0) {
            // HwBinder not available on this device or not accessible to
            // this process.
            return nullptr;
        }

        waitForHwServiceManager();

        while (gDefaultServiceManager == nullptr) {
            gDefaultServiceManager =
                fromBinder<IServiceManager1_2, BpHwServiceManager, BnHwServiceManager>(
                    ProcessState::self()->getContextObject(nullptr));
            if (gDefaultServiceManager == nullptr) {
                LOG(ERROR) << "Waited for hwservicemanager, but got nullptr.";
                sleep(1);
            }
        }
    }

    return gDefaultServiceManager;
}
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• /dev/vndbinder获取方法defaultServiceManager()，从上面2.3查看与/dev/binder共用一套libbinder，这里通过ProcessState::self()与ProcessState::initWithDriver("/dev/vndbinder")切换，默认kDefaultDriver = "/dev/binder"；因此两者使用时，每次只能指定一个设备节点，不能同时使用。左图mediaserver.rc启动，右图CameraProvider进程启动（CameraProvider进程-Android12）