Upgrading from health@1.0 HAL

0. Remove android.hardware.health@1.0* from PRODUCT_PACKAGES
   in device/<manufacturer>/<device>/device.mk

1. If the device does not have a vendor-specific libhealthd AND does not
   implement storage-related APIs, just do the following:

    PRODUCT_PACKAGES += android.hardware.health@2.0-service

   Otherwise, continue to Step 2.

2. Create directory
   device/<manufacturer>/<device>/health

3. Create device/<manufacturer>/<device>/health/Android.bp
   (or equivalent device/<manufacturer>/<device>/health/Android.mk)

cc_binary {
    name: "android.hardware.health@2.0-service.<device>",
    init_rc: ["android.hardware.health@2.0-service.<device>.rc"],
    proprietary: true,
    relative_install_path: "hw",
    srcs: [
        "HealthService.cpp",
    ],

    cflags: [
        "-Wall",
        "-Werror",
    ],

    static_libs: [
        "android.hardware.health@2.0-impl",
        "android.hardware.health@1.0-convert",
        "libhealthservice",
        "libbatterymonitor",
    ],

    shared_libs: [
        "libbase",
        "libcutils",
        "libhidlbase",
        "libhidltransport",
        "libutils",
        "android.hardware.health@2.0",
    ],

    header_libs: ["libhealthd_headers"],

    overrides: [
        "healthd",
    ],
}

    3.1 (recommended) To remove healthd from the build, keep "overrides" section.
    3.2 To keep healthd in the build, remove "overrides" section.

4. Create device/<manufacturer>/<device>/health/android.hardware.health@2.0-service.<device>.rc

service vendor.health-hal-2-0 /vendor/bin/hw/android.hardware.health@2.0-service.<device>
    class hal
    user system
    group system
    file /dev/kmsg w

5. Create device/<manufacturer>/<device>/health/HealthService.cpp:

#include <health2/service.h>
int main() { return health_service_main(); }

6. libhealthd dependency:

6.1 If the device has a vendor-specific libhealthd.<soc>, add it to static_libs.

6.2 If the device does not have a vendor-specific libhealthd, add the following
    lines to HealthService.cpp:

#include <healthd/healthd.h>
void healthd_board_init(struct healthd_config*) {}

int healthd_board_battery_update(struct android::BatteryProperties*) {
    // return 0 to log periodic polled battery status to kernel log
    return 0;
}

7. Storage related APIs:

7.1 If the device does not implement IHealth.getDiskStats and
    IHealth.getStorageInfo, add libstoragehealthdefault to static_libs.

7.2 If the device implements one of these two APIs, add and implement the
    following functions in HealthService.cpp:

void get_storage_info(std::vector<struct StorageInfo>& info) {
    // ...
}
void get_disk_stats(std::vector<struct DiskStats>& stats) {
    // ...
}

8. Update necessary SELinux permissions. For example,

# device/<manufacturer>/<device>/sepolicy/vendor/file_contexts
/vendor/bin/hw/android\.hardware\.health@2\.0-service.<device> u:object_r:hal_health_default_exec:s0

# device/<manufacturer>/<device>/sepolicy/vendor/hal_health_default.te
# Add device specific permissions to hal_health_default domain, especially
# if Step 6.1 or Step 7.2 is done.

9. Implementing health HAL in recovery. The health HAL is used for battery
status checks during OTA for non-A/B devices. If the health HAL is not
implemented in recovery, is_battery_ok() will always return true.

9.1 If the device does not have a vendor-specific libhealthd, nothing needs to
be done. A "backup" implementation is provided in
android.hardware.health@2.0-impl-default, which is always installed to recovery
image by default.

9.2 If the device do have a vendor-specific libhealthd, implement the following
module and include it in PRODUCT_PACKAGES (replace <device> with appropriate
strings):

// Android.bp
cc_library_shared {
    name: "android.hardware.health@2.0-impl-<device>",
    recovery_available: true,
    relative_install_path: "hw",
    static_libs: [
        "android.hardware.health@2.0-impl",
        "libhealthd.<device>"
        // Include the following if Step 7.1, otherwise do Step 7.2
        "libhealthstoragedefault",
    ],
    srcs: [
        "HealthImpl.cpp",
    ],
    overrides: [
        "android.hardware.health@2.0-impl-default",
    ],
}

// HealthImpl.cpp
#include <health2/Health.h>
#include <healthd/healthd.h>
using android::hardware::health::V2_0::IHealth;
using android::hardware::health::V2_0::implementation::Health;
extern "C" IHealth* HIDL_FETCH_IHealth(const char* name) {
    const static std::string providedInstance{"default"};
    if (providedInstance != name) return nullptr;
    return Health::initInstance(&gHealthdConfig).get();
}

# device.mk
PRODUCT_PACKAGES += android.hardware.health@2.0-impl-<device>