Android Partioning

Modern Android devices use dynamic partitions, A/B slots, and GKI separation, so partition layouts are more modular and OTA-friendly than pre-Treble devices.

Boot Chain Partiitons

• boot Partiiton
  • Built using mkbootimg
  • Contains:
    • Kernel (Image, Image.gz, etc)
    • **Vendor ramdisk fragments (Android 12+)
    • Bootconfig
  • Verified by AVB
  • Overwritten by OTA
  • With GKI (Android 12+), the kernel is generic and vendor modules move to vendor_dlkm
• init_boot Partition (Android 13+)
  • Contains the generic Ramdisk
  • Required for devices launching with Android 13+
  • Boot partition now contains vendor ramdisk fragments
  • Enables cleaner separation between generic and vendor init
• vbmeta Partition
  • Part of AVB 2.0
  • Contains hash/signature metadata for:
    • boot
    • system
    • vendor
    • product
    • etc.
  • Prevents tampering
  • There is also:
    • vbmeta_system
    • vbmeta_vendor

Core System Partitions (Treble)

• system Partition
  • Android framework
  • System apps
  • /system/bin, /system/lib*
  • APEX packages (mounted at runtime)
• vendor Partition
  • SoC vendor binaries
  • HAL implementations
  • Vendor services
  • Required for treble compliance
• product Partition
  • Product-specific customizations
  • Product-specific apps and overlays
  • Was introduced to modularize system/vendor
• system_ext Partition
  • Extensions to system image
  • OEM additions that extend framework APIs
  • Helps avoid modifying /system
• odm Partition
  • ODM customizations to SoC BSP
  • Board-specific HALs
  • Device SKU variations

Kernel Module Partitions (GKI)

• vendor_dlkm
  • Vendor kernel modules
• odm_dlkm
  • ODM-specific kernel modules
• system_dlkm
  • GKI system kernel modules (if used)

Update/Encryption/Security Partitions

• A/B Slot Partitions:
  • On seamless update devices:
    • boot_a, boot_b
    • system_a, system_b
    • etc.
  • Inactive slot is updated, then switched
• recovery Partition
  • Stores recovery image (non-A/B devices, initial A/B devices)
  • On A/B devices:
    • Recovery ramdisk might be inside boot or init_boot
    • No standalone partition
• cache Partition (Legacy)
  • Used for OTA staging (non-A/B devices)
  • Obsolete now
• misc Partition
  • Stores:
    • Bootloader control block (BCB)
    • Recovery commands
    • Slot metadata (before)
  • Still present even on A/B devices
• userdata Partition
  • /data
  • User apps and data
  • File-based Encryption (FBE)
  • Adoptable storage metadata
• metadata Partition
  • Stores metadata encryption keys
  • Required for:
    • FBE
    • Metadata encryption
    • Virtual A/B snapshots
  • Critical for devices
• persist Partition
  • Calibration data:
    • WiFi
    • Bluetooth
    • Sensors
  • Factory provisioning data
  • Not wiped on factory reset

Radio & Firmware Partitions

• radio/modem
  • Baseband firmware
  • for cellular devices
• dsp/bluetooth/abl/xbl
  • xbl - Qualcomm bootloader stage
  • abl - Android bootloader
  • tz - TrustZone firmware
  • There are SoC-specific and not standardized

Trusted Execution Environment

• tos/tz
  • Stores trusted OS
  • Example: Trusty
  • Used for:
    • Keymaster
    • Gatekeeper
    • Secure Storage

Dynamic Partitions

• super
  • A container partition holding logical partitions:
    • system
    • vendor
    • product
    • etc.
  • Managed by:
    • lpmake
    • lpunpack
  • Advantages:
    • Resization partitions
    • No fixed size wastage
    • Easier OTA resizing

Snapshot Partitions (Virtual A/B)

• With Virtual A/B (Android 11+):
  • Snapshots stored in userdata
  • Uses:
    • dm-snapshot
    • COW (Copy-on-write)
  • Eliminates need for full duplicate partitions
  • Reduces storage overhead compared to classic A/B