Introduction to Dynamic Partitions and the `super` Image

Modern Android devices leverage a powerful partitioning scheme known as Dynamic Partitions, introduced with Android 10. This system replaces the static, fixed-size partitions (like system, vendor, product) with a flexible, logical volume management layer residing within a single physical partition called super. This architecture allows OEMs to push OTA updates that dynamically resize partitions, offering greater flexibility and reducing device fragmentation.

For advanced users, custom ROM developers, or those seeking to optimize their device’s storage layout, understanding and manipulating the super image is a crucial skill. This guide provides a practical, expert-level lab to deconstruct, redesign, and flash a custom super image, enabling tailored partition layouts beyond stock configurations.

Prerequisites and Tools

Before diving in, ensure you have the following:

• A Linux environment (Ubuntu/Debian recommended) or Windows Subsystem for Linux (WSL).
• ADB and Fastboot tools installed and configured.
• A target Android device with an unlocked bootloader.
• Familiarity with command-line operations.
• Necessary tools for dynamic partition manipulation:lpunpack, lpadd, lpmake, img2simg (from AOSP source or pre-built binaries).
• A stock super.img from your device’s firmware, or access to a full factory image.

Understanding the `super` Partition Structure

The super partition isn’t a traditional filesystem; rather, it’s a container for Logical Partition Manager (LPM) metadata and a collection of underlying sparse images for partitions like system, vendor, product, odm, etc. The metadata defines the layout: which logical partitions belong to which update groups (e.g., q_dynamic_partitions_a, q_dynamic_partitions_b for A/B slots), their sizes, and their properties.

Key Components:

• Metadata: Describes the logical partitions, their names, sizes, and membership in update groups.
• Groups: Collections of logical partitions. Devices supporting A/B updates typically have two groups (e.g., `q_dynamic_partitions_a` and `q_dynamic_partitions_b`), allowing seamless updates.
• Partitions: The actual logical partitions like `system`, `vendor`, `product`, `odm`, etc., which reside within the `super` block device.

Lab Setup: Extracting Your Stock `super` Image

First, we need to obtain and deconstruct your device’s existing super.img.

1. Extract `super.img` from Device (if not available in factory image)

   Boot your device into fastboot mode. If your device supports fastbootd (Android 11+), you might be able to directly dump the super partition.

   adb reboot fastbootfastboot --set-active=a # Or b, if you know which slot is activefastboot reboot fastbootd # If availablefastboot getvar all # Look for super_partition_sizefastboot read super super.img

   If fastbootd is not available or read super fails, you’ll need to extract it from a factory image or a device dump.

2. Deconstruct the `super` Image with `lpunpack`

   The lpunpack tool is essential for extracting the contents of a super.img.

   lpunpack --output ./extracted_super super.img

   This command will create a directory named extracted_super containing the individual .img files (e.g., system.img, vendor.img) and a lp_metadata file. Inspect the metadata to understand the original layout:

   lpunpack --dump-json lp_metadata

   This will output a JSON structure detailing the groups, partitions, and their properties. Pay close attention to maximum_size for groups and size for individual partitions. Note the block size (often 4096 bytes) and metadata size (e.g., 65536 bytes) which are crucial for re-creating the image.

Designing Your Custom Partition Layout

The core of this lab is defining your desired partition layout. Common scenarios include:

• Increasing the size of system for larger GApps or custom binaries.
• Shrinking vendor to free up space for other partitions.
• Adding a new logical partition (e.g., user_storage, aosp_build) for specific purposes.

Based on the lpunpack --dump-json lp_metadata output, you’ll create a new JSON file (e.g., custom_layout.json) that dictates the structure for lpmake. The structure typically looks like this:

{

        
        
        

            

                
            
            

                
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