Block diagram
The metadata stored by Android at the beginning of a "super" partition, which is what it calls a disk partition that holds one or more Dynamic Partitions. Dynamic Partitions do more or less the same thing that LVM does on Linux, allowing Android to map ranges of non-contiguous extents to a single logical device. This metadata holds that mapping.
This page hosts a formal specification of Android Dynamic Partitions metadata using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: android_super
title: Android Dynamic Partitions metadata
application: Android
file-extension: img
tags:
- android
- filesystem
license: CC0-1.0
ks-version: 0.9
bit-endian: le
endian: le
doc: |
The metadata stored by Android at the beginning of a "super" partition, which
is what it calls a disk partition that holds one or more Dynamic Partitions.
Dynamic Partitions do more or less the same thing that LVM does on Linux,
allowing Android to map ranges of non-contiguous extents to a single logical
device. This metadata holds that mapping.
doc-ref:
- https://source.android.com/docs/core/ota/dynamic_partitions
- https://android.googlesource.com/platform/system/core/+/refs/tags/android-11.0.0_r8/fs_mgr/liblp/include/liblp/metadata_format.h
instances:
root:
pos: 0x1000
type: root
types:
root:
seq:
- id: primary_geometry
size: 0x1000
type: geometry
- id: backup_geometry
type: geometry
size: 0x1000
- id: primary_metadata
size: primary_geometry.metadata_max_size
type: metadata
repeat: expr
repeat-expr: primary_geometry.metadata_slot_count
- id: backup_metadata
# These attributes are intentionally taken from primary_geometry, even
# for backup_metadata. The first non-corrupt geometry specifier dictates
# the layout of both primary and backup metadata.
size: primary_geometry.metadata_max_size
type: metadata
repeat: expr
repeat-expr: primary_geometry.metadata_slot_count
geometry:
seq:
- id: magic
contents: 'gDla'
- id: struct_size
type: u4
- id: checksum
size: 32
doc: |
SHA-256 hash of struct_size bytes from beginning of geometry,
calculated as if checksum were zeroed out
- id: metadata_max_size
type: u4
- id: metadata_slot_count
type: u4
- id: logical_block_size
type: u4
metadata:
seq:
- id: magic
contents: '0PLA'
- id: major_version
type: u2
- id: minor_version
type: u2
- id: header_size
type: u4
- id: header_checksum
size: 32
doc: |
SHA-256 hash of header_size bytes from beginning of metadata,
calculated as if header_checksum were zeroed out
- id: tables_size
type: u4
- id: tables_checksum
size: 32
doc: SHA-256 hash of tables_size bytes from end of header
- id: partitions
type: table_descriptor(table_kind::partitions)
- id: extents
type: table_descriptor(table_kind::extents)
- id: groups
type: table_descriptor(table_kind::groups)
- id: block_devices
type: table_descriptor(table_kind::block_devices)
enums:
table_kind:
0: partitions
1: extents
2: groups
3: block_devices
types:
table_descriptor:
params:
- id: kind
type: u1
enum: table_kind
-affected-by: 135
seq:
- id: offset
type: u4
- id: num_entries
type: u4
- id: entry_size
type: u4
instances:
table:
pos: _parent.header_size + offset
size: entry_size
type:
switch-on: kind
cases:
'table_kind::partitions': partition
'table_kind::extents': extent
'table_kind::groups': group
'table_kind::block_devices': block_device
repeat: expr
repeat-expr: num_entries
partition:
seq:
- id: name
size: 36
type: strz
encoding: UTF-8
- id: attr_readonly
type: b1
- id: attr_slot_suffixed
type: b1
- id: attr_updated
type: b1
- id: attr_disabled
type: b1
- id: attrs_reserved
type: b28
- id: first_extent_index
type: u4
- id: num_extents
type: u4
- id: group_index
type: u4
extent:
seq:
- id: num_sectors
type: u8
- id: target_type
type: u4
enum: target_type
- id: target_data
type: u8
- id: target_source
type: u4
enums:
target_type:
0: linear
1: zero
group:
seq:
- id: name
size: 36
type: strz
encoding: UTF-8
- id: flag_slot_suffixed
type: b1
- id: flags_reserved
type: b31
- id: maximum_size
type: u8
block_device:
seq:
- id: first_logical_sector
type: u8
- id: alignment
type: u4
- id: alignment_offset
type: u4
- id: size
type: u8
- id: partition_name
size: 36
type: strz
encoding: UTF-8
- id: flag_slot_suffixed
type: b1
- id: flags_reserved
type: b31