ODM partitions

Android 10 includes support for building odm partitions using the Android build system.

About ODM partitions

Original design manufacturers (ODMs) customize system-on-chip (SoC) vendor board-support packages (BSPs) to their specific devices (their boards). This enables them to implement kernel modules for board-specific components, board-specific daemons, or their own features on hardware abstraction layers (HALs). They might also want to replace or customize SoC components.

In lower Android releases, such customizations prevented the use of a single vendor image for devices with the same SoC (or with different SoCs, but in the same family). In Android 10 and higher, you can use a separate odm partition for customizations, which enables you to use a single vendor image for multiple hardware SKUs.

Use product and ODM partitions

Android 9 added support for building product partitions, enabling the use of a single system image for multiple software SKUs supplied by different product.img images. While the product partition is intended for software SKUs, the odm partition is intended for hardware SKUs.

With dedicated product and ODM partitions, you can use the system partition to host generic code for sharing among many software SKUs, and the vendor partition to host SoC-specific BSP code to share among multiple devices based on the given SoC.

Using separate partitions has disadvantages, such as the difficulty in managing disk space (for example, you must reserve a limited amount of space for future growth). However, Android 10 support for dynamic partitions removes the disk issue, and makes repartitioning a device during an over-the-air (OTA) update possible.

ODM components

The odm partition contains the following ODM-specific components (similar to the vendor partition), listed in the following table.

ODM-specific component Location
Loadable kernel modules (LKMs) /odm/lib/modules/*.ko
Native libraries /odm/lib[64]
HALs /odm/lib[64]/hw
SEPolicy /odm/etc/selinux
VINTF object data /odm/etc/vintf
init.rc files /odm/etc/init
System properties /odm/build.prop
Runtime resource overlays (RROs) /odm/overlay/*.apk
Apps /odm/app/*.apk
Priv-apps /odm/priv-app/*.apk
Java libraries /odm/framework/*.jar
Android Framework system configs /odm/etc/sysconfig/* and /odm/etc/permissions/*

No custom images

Don't use custom images because they lack support for the following:

  • Installation of a module to a specific target. Custom images support copying artifacts into an image, but can't install a module into a specific partition by specifying the target partition as a part of a build rule.
  • Soong. custom_images can't be built using the Soong build system.
  • OTA update. Custom images are used as factory ROM images that can't be OTA-ed.

Maintain ABIs between partitions

The odm partition is an extension of the vendor partition. When considering application binary interface (ABI) stability, keep the following architecture in mind.

Maintaining ABI between partitions

Figure 1. Maintaining ABI between partitions.

  • There's no ABI stability between odm and vendor partitions. Both partitions must be upgraded at the same time.
  • The odm and vendor partitions can depend on each other, but the vendor partition must work without an odm partition.
  • The ABI between odm and system is the same as the ABI between vendor and system.

Direct interaction between the product partition and the vendor or odm partition isn't allowed. (This is enforced by SEpolicy.)

Implement ODM partitions

Before implementing a new partition, review the related AOSP changes.

Set up ODM partitions

To set up odm partitions, include these build flags:

  • BOARD_ODMIMAGE_PARTITION_SIZE for a fixed partition size
  • BOARD_ODMIMAGE_FILE_SYSTEM_TYPE file system type used for the ODM image
  • PRODUCT_ODM_PROPERTIES for /odm/build.prop for use within a $(call inherit-product path/to/device.mk), as in PRODUCT_ODM_PROPERTIES += product.abc=ok

Install a module to an ODM partition

Use these build flags to install a module to an odm partition:

  • device_specific: true in Android.bp
  • LOCAL_ODM_MODULE := true in Android.mk

Enable Verified Boot

To prevent malicious software from tampering with odm partitions, enable Android Verified Boot (AVB) for those partitions (just as you do for vendor and system partitions).

To enable AVB, include the build flag BOARD_AVB_ODM_ADD_HASHTREE_FOOTER_ARGS. For details on configuring AVB on dynamic partitions, see AVB configuration changes.

Treat /odm as another /vendor partition

To ensure that the system handles the odm partition as a vendor partition, replace any hard-coded vendor references with a set of hardware-oriented partitions (currently odm and vendor). Notable vendor reference locations in the platform include dynamic linker, package manager, and shell/libc.