SdkExtensions module

SdkExtensions is a module that decides the extension SDK level of the device, and provides APIs for applications to query the extension SDK level.

General information

Structure

The module is packaged in an apex, com.android.sdkext, and has two components:

bin/derive_sdk: Native binary that runs early in the device boot process and reads metadata of other modules, to set system properties relating to the extension SDK (for instance build.version.extensions.r).
javalib/framework-sdkextension.jar: This is a jar on the bootclasspath that exposes APIs to applications to query the extension SDK level.

Deriving extension SDK level

derive_sdk is a program that reads metadata stored in other apex modules, in the form of binary protobuf files in subpath etc/sdkinfo.binarypb inside each apex. The structure of this protobuf can be seen here. The exact steps for converting a set of metadata files to actual extension versions is likely to change over time, and should not be depended upon.

Reading extension SDK level

The module exposes a java class SdkExtensions in the package android.os.ext. The method getExtensionVersion(int) can be used to read the version of a particular sdk extension, e.g. getExtensionVersion(Build.VERSION_CODES.R).

Developer information

Adding a new extension version

For every new Android SDK level a new extension version should be defined. These are the steps necessary to do that:

Add the new modules in this extension version to the SdkModule enum in sdk.proto.
Update derive_sdk.cpp by:

mapping the modules' package names to the new enum values
creating a new set with the new enum values
set a new sysprop to the value of GetSdkLevel with the new enum set
add a unit test to derive_sdk_test.cpp verifying the new extensions works

Make the SdkExtensions.getExtensionVersion API support the new extensions.
Extend the CTS test to verify the above two behaviors.
Update RollbackManagerServiceImpl#getExtensionVersions to account for the new extension version.