Bug: 146511931

Clone this repo:
  1. 90c6c2a Fix typo in args parsing by Alan Stokes · 13 days ago master
  2. e2d87eb Merge "Derive STANDALONE_SYSTEMSERVER_JARS from systemserverclasspath.pb." am: 7652b77ac1 by Treehugger Robot · 8 weeks ago
  3. 7652b77 Merge "Derive STANDALONE_SYSTEMSERVER_JARS from systemserverclasspath.pb." by Treehugger Robot · 8 weeks ago
  4. 021fc78 Update reference to VERSION_CODES.S am: dcf2160033 by Anton Hansson · 8 weeks ago
  5. dcf2160 Update reference to VERSION_CODES.S by Anton Hansson · 8 weeks ago

SdkExtensions module

SdkExtensions module is responsible for:

  • deciding the extension SDK level of the device;
  • providing APIs for applications to query the extension SDK level;
  • determining the values for the BOOTCLASSPATH, DEX2OATBOOTCLASSPATH, and SYSTEMSERVERCLASSPATH environment variables.

General information


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

  • bin/derive_classpath: a native binary that runs early in the device boot process. It reads individual classpath configs files from the system and other modules, merges them, and defines the definition of *CLASSPATH environ variables.
  • 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.pb 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).

Deriving classpaths

derive_classpath service reads and merges individual config files in the /system/etc/classpaths/ and /apex/*/etc/classpaths. Each config stores protobuf message from classpaths.proto in a proto binary format. Exact merging algorithm that determines the order of the classpath entries is described in derive_classpath.cpp and may change over time.

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.