The Evolution of Android Partitioning: Dynamic Partitions and A/B Updates

Modern Android devices, especially those launched with Android 10 or newer, utilize a sophisticated storage architecture known as Dynamic Partitions. This paradigm shift moves away from a fixed, hard-coded partition layout towards a flexible, software-managed system. Paired with the A/B (seamless updates) system, dynamic partitions allow for highly efficient over-the-air (OTA) updates, reducing downtime and enhancing reliability during system upgrades.

At the heart of dynamic partitions lies the super partition, a single physical partition that hosts all other logical partitions such as system, vendor, product, odm, and system_ext. These logical partitions are not fixed in size; their storage can be dynamically allocated and resized from the free space within the super partition. While this offers immense flexibility for device manufacturers, it introduces new challenges for power users, custom ROM developers, and kernel enthusiasts who need to backup, restore, or modify these critical system components.

The Challenge: Managing Dynamic Partitions for Custom Development

In the era of static partitions, backing up an entire Android system was relatively straightforward: use dd to dump individual partitions like /dev/block/by-name/system or /dev/block/by-name/vendor. However, with dynamic partitions, this approach is no longer viable for logical partitions. The metadata that defines the size, location, and presence of these logical partitions is stored within the super partition itself, managed by the Logical Partition Manager (LPM).

When flashing custom ROMs, experimenting with different kernels, or attempting to resize partitions, the integrity of the super partition and its internal metadata becomes paramount. A simple dd of a logical partition without proper context can lead to an unbootable device. The real challenge lies in creating a robust and automatable method to backup and restore the entire super partition, ensuring that all logical partition definitions and their contents are preserved correctly.

Understanding the Super Partition and Logical Partition Manager (LPM)

The super partition acts as a container for all logical partitions. It contains a partition table and allocation metadata that the Logical Partition Manager (LPM) uses to understand and manage the logical volumes within. When the system boots, the kernel uses this metadata to map the logical partitions to their respective areas within the super partition.

Tools like lpunpack and lpmake (often found in the Android Open Source Project (AOSP) source or prebuilt alongside platform-tools) are essential for interacting with super images. lpunpack allows you to extract individual logical partition images from a super image, while lpmake can create a super image from a collection of logical partition images. For backup and restore, however, our primary focus will be on the raw super image itself, as it encapsulates the entire dynamic partition structure.

Prerequisites for Automated Management

• An Android device with Dynamic Partitions (typically Android 10+), with an unlocked bootloader.
• A host PC with ADB and Fastboot installed and correctly configured in your system’s PATH.
• A Linux-based environment (or WSL/Cygwin on Windows) for scripting and running tools like lpunpack/lpmake if needed.
• Basic familiarity with shell scripting and command-line operations.

Step-by-Step Guide: Scripting Dynamic Partition Backup & Restore

Step 1: Preparing Your Environment

Ensure adb and fastboot are accessible from your terminal. Connect your device via USB and verify it’s recognized:

adb devices
fastboot devices

Your device should be listed as ‘device’ under adb devices, and nothing (or ‘waiting for device’) under fastboot devices initially. If you plan to extract logical partitions, obtain the lpunpack utility compatible with your Android version.

Step 2: Identifying Your Super Partition

The exact device path for the super partition can vary slightly between devices, though /dev/block/by-name/super is common. You can find it using adb shell:

adb shell

        
        
        

            

                
            
            

                
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