Understanding Android VNDK/VSDK Snapshot Architecture

This article provides a comprehensive analysis of Android's VNDK (Vendor NDK) and VSDK (Vendor SDK) Snapshot architecture, which are key components of the Treble architecture designed to address Android version fragmentation.

Background:

To solve Android version fragmentation, Google introduced the Treble architecture, which provides stable new SoC vendor interfaces using HIDL/Stable AIDL (Binder-based). This architecture decouples system framework from vendor HAL, making Vendor Freeze possible. Research shows that 30-40% of AOSP vendor repositories were coupled with system components, including framework, prebuilts, external, platform, ODM, and build repositories.

Starting from Android R, Google enhanced the system/vendor interface capabilities through VNDK and VSDK snapshot solutions, enabling system components to be precompiled into vendor Snapshots for use across different Android versions.

VNDK Basic Concepts:

VNDK categorizes Native libraries to control system/vendor coupling:

Core Library: Only in system image, used only by system modules, cannot be depended on by vendor, vendor_available, vndk, or vndk-sp libraries

Vendor-only Library: Only for vendor use, binary in vendor image

Vendor_available Library: Used by vendor image, exists in both vendor and core variants, packaged in both images

VNDK Library: Used by vendor modules, binary in system image

VNDK-SP Library: Directly used by vendor, indirectly used by system, binary in system image

LLNDK Library: Maintained by Google, used by both system and vendor, can double load

VSDK Concepts:

VSDK includes VNDK plus Vendor Snapshot. Vendor Snapshot contains: dynamic/static libraries with vendor or vendor_available flags, static VNDK libraries with vendor_available flag, and executables or target files with vendor flags.

Snapshot Generation Process:

The Snapshot generation involves three phases:

Generate Phase: Produces prebuilt snapshot modules from system source code for vendor image compilation

Install Phase: Python scripts install prebuilt modules to designated source directories and generate corresponding Android.bp files

Use Phase: Setting BOARD_VNDK_VERSION triggers the build system to use pre-generated Snapshots, blocking source compilation for related modules

Benefits:

Improved vendor component compilation efficiency

Enhanced code cognition management - decoupled repositories can remove vendor coupling repositories

Better support for independent development of system/vendor components