Introduction to Dynamic Partitions and DTBOs

Android’s Project Treble introduced Dynamic Partitions, a significant architectural change that allows device manufacturers to update OS components without requiring a full device reflash. This system consolidates traditional partitions like system, vendor, product, and others into a single ‘super’ partition, whose logical subdivisions can be resized, added, or removed during over-the-air (OTA) updates. This flexibility is crucial for managing varying image sizes across different Android versions.

At the heart of low-level hardware configuration on Android devices lies the Device Tree (DT) and its extensions, Device Tree Overlays (DTBOs). The Device Tree provides a description of the hardware components to the Linux kernel, including CPU, memory, peripherals, and storage. DTBOs extend this capability by allowing runtime modifications or additions to the base device tree, enabling manufacturers to support multiple hardware configurations with a single kernel binary.

For custom ROM developers and advanced users, understanding and modifying DTBOs is a powerful skill, especially when aiming to customize dynamic partition sizes beyond what’s defined by default. This guide will walk you through the process of extracting, modifying, and flashing custom DTBOs to achieve tailored dynamic partition layouts on Android devices.

Understanding DTBOs and Their Role in Partition Management

A Device Tree Overlay is essentially a `.dtb` (Device Tree Blob) that contains additions or modifications to another base `.dtb`. When an Android device boots, the bootloader loads the base DTB and then applies one or more DTBOs from the `dtbo.img` partition. These overlays can modify various aspects of the device tree, including memory allocation, peripheral enablement, and crucially for our purpose, properties related to storage.

Within the device tree, storage configurations for dynamic partitions are often defined under nodes like `/firmware/android/super` or similar paths. Here, properties such as android,super-partitions and individual logical partition definitions (e.g., system, vendor) can specify their initial sizes, read-only status, and other attributes. The key property we’ll target for resizing is typically android,size or simply size, usually expressed in bytes as a hexadecimal value.

Prerequisites and Tools

Before you begin, ensure you have the following tools and knowledge:

• Android SDK Platform Tools: ADB and Fastboot installed and configured.
• Device Tree Compiler (DTC): Essential for decompiling `.dtbo` files into human-readable `.dts` source and recompiling them. Usually available in your Linux distribution’s package manager (e.g., sudo apt install device-tree-compiler) or from the Android kernel source.
• mkdtimg: A utility for creating and extracting `dtbo.img` files, often found in Android source trees (`./out/host/linux-x86/bin/mkdtimg`).
• A working Android device: With an unlocked bootloader and preferably a custom recovery like TWRP for easier flashing and debugging.
• Basic Linux command-line proficiency.

Step-by-Step Guide: Modifying DTBO for Custom Partition Sizes

Step 1: Extracting the Original DTBO Image

First, you need to obtain the `dtbo.img` from your device. You can often pull this directly if you have a custom recovery:

adb pull /dev/block/by-name/dtbo dtbo.img

Alternatively, if you’re working with a ROM package, you can often find `dtbo.img` within the zip file, sometimes nested in a `payload.bin` or similar archive, which requires tools like `payload-dumper-go` to extract.

Step 2: Decompiling the DTBO Image

The `dtbo.img` is typically a concatenated image containing one or more `.dtbo` files. You’ll need `mkdtimg` to extract these individual overlays:

mkdtimg dump dtbo.img -o extracted_dtbos/

This command will create a directory `extracted_dtbos` containing files like `dtbo-0.dtbo`, `dtbo-1.dtbo`, etc. Now, decompile each `.dtbo` file into a `.dts` (Device Tree Source) file using `dtc`:

dtc -I dtb -O dts -o dtbo-0.dts extracted_dtbos/dtbo-0.dtbo

Repeat this for all extracted `.dtbo` files. You can also use a loop:

for f in extracted_dtbos/*.dtbo; do dtc -I dtb -O dts -o "${f%.dtbo}.dts" "$f"; done

Step 3: Identifying and Modifying Partition Nodes

Open each `.dts` file you decompiled in a text editor. You are looking for nodes that define the `super` partition and its logical volumes. Search for keywords like `super`, `android,super-partitions`, `partitions`, `size`, `system`, `vendor`, `product`. The exact path and property names can vary slightly between devices and kernel versions.

A common structure might look like this:

/ {    firmware {        android {            super@0 {                compatible =

        
        
        

            

                
            
            

                
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