Android HAL 学习笔记_android.mk 编译库到某个路径 vendor/lib64/hw

• HAL 层文件在系统中的路径

Android系统编译的硬件抽象库存放于/system/lib64/hw目录和/vendor/lib64/hw/下:

console:/ # ls /system/lib64/hw/
android.hidl.memory@1.0-impl.so

console:/ # ls /vendor/lib64/hw/
android.hardware.audio.effect@4.0-impl.so
android.hardware.audio@4.0-impl.so
android.hardware.bluetooth@1.0-impl.so
android.hardware.boot@1.0-impl.so
android.hardware.broadcastradio@1.0-impl.so
android.hardware.camera.provider@2.4-impl.so
android.hardware.gatekeeper@1.0-impl.so
android.hardware.gnss@1.0-impl-mediatek.so
android.hardware.graphics.allocator@2.0-impl.so
android.hardware.graphics.composer@2.1-impl.so
android.hardware.graphics.mapper@2.0-impl.so
android.hardware.keymaster@3.0-impl.so
android.hardware.light@2.0-impl.so
android.hardware.memtrack@1.0-impl.so
android.hardware.renderscript@1.0-impl.so
android.hardware.sensors@1.0-impl.so
android.hardware.thermal@1.0-impl.so
audio.primary.mt2712.so
bootctrl.mt2712.so
camera.v4l2.so
gatekeeper.default.so
gps.mt2712.so
gralloc.default.so
gralloc.mt2712.so
hwcomposer.mt2712.so
libSoftGatekeeper.so
lights.mt2712.so
memtrack.mt2712.so
sensors.mt2712.so
thermal.mt2712.so
vulkan.mt2712.so

• HAL 层文件加载入口

Android系统提供的硬件抽象库访问接口hw_get_module：

hardware\libhardware\hardware.c

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

参数id为硬件抽象层模块ID，hw_module_t是硬件抽象层模块描述结构。

example：加载Gralloc模块

#define GRALLOC_HARDWARE_MODULE_ID  "gralloc"

hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &mModule);

hw_get_module函数是上层加载HAL库的入口，这里传入的模块ID名为：GRALLOC_HARDWARE_MODULE_ID 

按照hw_get_module的作法，它会在如下路径中查找与ID值匹配的库：

#define HAL_LIBRARY_PATH1 "/system/lib/hw"

#define HAL_LIBRARY_PATH2 "/vendor/lib/hw"