Flattened Devicetree Format: Python parsing library

Also referred to as Devicetree Blob (DTB). It is a flat binary encoding of data (primarily devicetree data, although other data is possible as well). The data is internally stored as a tree of named nodes and properties. Nodes contain properties and child nodes, while properties are name–value pairs.

The Devicetree Blobs (.dtb files) are compiled from the Devicetree Source files (.dts) through the Devicetree compiler (DTC).

On Linux systems that support this, the blobs can be accessed in /sys/firmware/fdt:

The encoding of strings used in the strings_block and structure_block is actually a subset of ASCII:

https://devicetree-specification.readthedocs.io/en/v0.3/devicetree-basics.html#node-names

Example files:

Application

["Linux", "Das U-Boot"]

File extension

dtb

KS implementation details

License: CC0-1.0
Minimal Kaitai Struct required: 0.9

References

This page hosts a formal specification of Flattened Devicetree Format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.

The Python runtime library can be installed from PyPI:

python3 -m pip install kaitaistruct

Code

Parse a local file and get structure in memory:

data = Dtb.from_file("path/to/local/file.dtb")

Or parse structure from a bytes:

from kaitaistruct import KaitaiStream, BytesIO

raw = b"\x00\x01\x02..."
data = Dtb(KaitaiStream(BytesIO(raw)))

After that, one can get various attributes from the structure by invoking getter methods like:

data.magic # => get magic

Python source code to parse Flattened Devicetree Format

dtb.py

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

from pkg_resources import parse_version
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
from enum import Enum


if parse_version(kaitaistruct.__version__) < parse_version('0.9'):
    raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))

class Dtb(KaitaiStruct):
    """Also referred to as Devicetree Blob (DTB). It is a flat binary encoding
    of data (primarily devicetree data, although other data is possible as well).
    The data is internally stored as a tree of named nodes and properties. Nodes
    contain properties and child nodes, while properties are name–value pairs.
    
    The Devicetree Blobs (`.dtb` files) are compiled from the Devicetree Source
    files (`.dts`) through the Devicetree compiler (DTC).
    
    On Linux systems that support this, the blobs can be accessed in
    `/sys/firmware/fdt`:
    
    * <https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-ofw>
    
    The encoding of strings used in the `strings_block` and `structure_block` is
    actually a subset of ASCII:
    
    <https://devicetree-specification.readthedocs.io/en/v0.3/devicetree-basics.html#node-names>
    
    Example files:
    
    * <https://github.com/qemu/qemu/tree/master/pc-bios>
    
    .. seealso::
       Source - https://devicetree-specification.readthedocs.io/en/v0.3/flattened-format.html
    
    
    .. seealso::
       Source - https://elinux.org/images/f/f4/Elc2013_Fernandes.pdf
    """

    class Fdt(Enum):
        begin_node = 1
        end_node = 2
        prop = 3
        nop = 4
        end = 9
    def __init__(self, _io, _parent=None, _root=None):
        self._io = _io
        self._parent = _parent
        self._root = _root if _root else self
        self._read()

    def _read(self):
        self.magic = self._io.read_bytes(4)
        if not self.magic == b"\xD0\x0D\xFE\xED":
            raise kaitaistruct.ValidationNotEqualError(b"\xD0\x0D\xFE\xED", self.magic, self._io, u"/seq/0")
        self.total_size = self._io.read_u4be()
        self.ofs_structure_block = self._io.read_u4be()
        self.ofs_strings_block = self._io.read_u4be()
        self.ofs_memory_reservation_block = self._io.read_u4be()
        self.version = self._io.read_u4be()
        self.min_compatible_version = self._io.read_u4be()
        if not self.min_compatible_version <= self.version:
            raise kaitaistruct.ValidationGreaterThanError(self.version, self.min_compatible_version, self._io, u"/seq/6")
        self.boot_cpuid_phys = self._io.read_u4be()
        self.len_strings_block = self._io.read_u4be()
        self.len_structure_block = self._io.read_u4be()

    class MemoryBlock(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.entries = []
            i = 0
            while not self._io.is_eof():
                self.entries.append(Dtb.MemoryBlockEntry(self._io, self, self._root))
                i += 1



    class FdtBlock(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.nodes = []
            i = 0
            while True:
                _ = Dtb.FdtNode(self._io, self, self._root)
                self.nodes.append(_)
                if _.type == Dtb.Fdt.end:
                    break
                i += 1


    class MemoryBlockEntry(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.address = self._io.read_u8be()
            self.size = self._io.read_u8be()


    class Strings(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.strings = []
            i = 0
            while not self._io.is_eof():
                self.strings.append((self._io.read_bytes_term(0, False, True, True)).decode(u"ASCII"))
                i += 1



    class FdtProp(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.len_property = self._io.read_u4be()
            self.ofs_name = self._io.read_u4be()
            self.property = self._io.read_bytes(self.len_property)
            self.padding = self._io.read_bytes((-(self._io.pos()) % 4))

        @property
        def name(self):
            if hasattr(self, '_m_name'):
                return self._m_name if hasattr(self, '_m_name') else None

            io = self._root.strings_block._io
            _pos = io.pos()
            io.seek(self.ofs_name)
            self._m_name = (io.read_bytes_term(0, False, True, True)).decode(u"ASCII")
            io.seek(_pos)
            return self._m_name if hasattr(self, '_m_name') else None


    class FdtNode(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.type = KaitaiStream.resolve_enum(Dtb.Fdt, self._io.read_u4be())
            _on = self.type
            if _on == Dtb.Fdt.begin_node:
                self.body = Dtb.FdtBeginNode(self._io, self, self._root)
            elif _on == Dtb.Fdt.prop:
                self.body = Dtb.FdtProp(self._io, self, self._root)


    class FdtBeginNode(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.name = (self._io.read_bytes_term(0, False, True, True)).decode(u"ASCII")
            self.padding = self._io.read_bytes((-(self._io.pos()) % 4))


    @property
    def memory_reservation_block(self):
        if hasattr(self, '_m_memory_reservation_block'):
            return self._m_memory_reservation_block if hasattr(self, '_m_memory_reservation_block') else None

        _pos = self._io.pos()
        self._io.seek(self.ofs_memory_reservation_block)
        self._raw__m_memory_reservation_block = self._io.read_bytes((self.ofs_structure_block - self.ofs_memory_reservation_block))
        _io__raw__m_memory_reservation_block = KaitaiStream(BytesIO(self._raw__m_memory_reservation_block))
        self._m_memory_reservation_block = Dtb.MemoryBlock(_io__raw__m_memory_reservation_block, self, self._root)
        self._io.seek(_pos)
        return self._m_memory_reservation_block if hasattr(self, '_m_memory_reservation_block') else None

    @property
    def structure_block(self):
        if hasattr(self, '_m_structure_block'):
            return self._m_structure_block if hasattr(self, '_m_structure_block') else None

        _pos = self._io.pos()
        self._io.seek(self.ofs_structure_block)
        self._raw__m_structure_block = self._io.read_bytes(self.len_structure_block)
        _io__raw__m_structure_block = KaitaiStream(BytesIO(self._raw__m_structure_block))
        self._m_structure_block = Dtb.FdtBlock(_io__raw__m_structure_block, self, self._root)
        self._io.seek(_pos)
        return self._m_structure_block if hasattr(self, '_m_structure_block') else None

    @property
    def strings_block(self):
        if hasattr(self, '_m_strings_block'):
            return self._m_strings_block if hasattr(self, '_m_strings_block') else None

        _pos = self._io.pos()
        self._io.seek(self.ofs_strings_block)
        self._raw__m_strings_block = self._io.read_bytes(self.len_strings_block)
        _io__raw__m_strings_block = KaitaiStream(BytesIO(self._raw__m_strings_block))
        self._m_strings_block = Dtb.Strings(_io__raw__m_strings_block, self, self._root)
        self._io.seek(_pos)
        return self._m_strings_block if hasattr(self, '_m_strings_block') else None