tools/binman/cbfs_util_test.py

#!/usr/bin/env python
# SPDX-License-Identifier: GPL-2.0+
# Copyright 2019 Google LLC
# Written by Simon Glass <sjg@chromium.org>

"""Tests for cbfs_util

These create and read various CBFSs and compare the results with expected
values and with cbfstool
"""

from __future__ import print_function

import io
import os
import shutil
import struct
import tempfile
import unittest

import cbfs_util
from cbfs_util import CbfsWriter
import elf
import test_util
import tools

U_BOOT_DATA           = b'1234'
U_BOOT_DTB_DATA       = b'udtb'
COMPRESS_DATA         = b'compress xxxxxxxxxxxxxxxxxxxxxx data'


class TestCbfs(unittest.TestCase):
    """Test of cbfs_util classes"""
    #pylint: disable=W0212
    @classmethod
    def setUpClass(cls):
        # Create a temporary directory for test files
        cls._indir = tempfile.mkdtemp(prefix='cbfs_util.')
        tools.SetInputDirs([cls._indir])

        # Set up some useful data files
        TestCbfs._make_input_file('u-boot.bin', U_BOOT_DATA)
        TestCbfs._make_input_file('u-boot.dtb', U_BOOT_DTB_DATA)
        TestCbfs._make_input_file('compress', COMPRESS_DATA)

        # Set up a temporary output directory, used by the tools library when
        # compressing files
        tools.PrepareOutputDir(None)

        cls.have_cbfstool = True
        try:
            tools.Run('which', 'cbfstool')
        except:
            cls.have_cbfstool = False

        cls.have_lz4 = True
        try:
            tools.Run('lz4', '--no-frame-crc', '-c',
                      tools.GetInputFilename('u-boot.bin'))
        except:
            cls.have_lz4 = False

    @classmethod
    def tearDownClass(cls):
        """Remove the temporary input directory and its contents"""
        if cls._indir:
            shutil.rmtree(cls._indir)
        cls._indir = None
        tools.FinaliseOutputDir()

    @classmethod
    def _make_input_file(cls, fname, contents):
        """Create a new test input file, creating directories as needed

        Args:
            fname: Filename to create
            contents: File contents to write in to the file
        Returns:
            Full pathname of file created
        """
        pathname = os.path.join(cls._indir, fname)
        tools.WriteFile(pathname, contents)
        return pathname

    def _check_hdr(self, data, size, offset=0, arch=cbfs_util.ARCHITECTURE_X86):
        """Check that the CBFS has the expected header

        Args:
            data: Data to check
            size: Expected ROM size
            offset: Expected offset to first CBFS file
            arch: Expected architecture

        Returns:
            CbfsReader object containing the CBFS
        """
        cbfs = cbfs_util.CbfsReader(data)
        self.assertEqual(cbfs_util.HEADER_MAGIC, cbfs.magic)
        self.assertEqual(cbfs_util.HEADER_VERSION2, cbfs.version)
        self.assertEqual(size, cbfs.rom_size)
        self.assertEqual(0, cbfs.boot_block_size)
        self.assertEqual(cbfs_util.ENTRY_ALIGN, cbfs.align)
        self.assertEqual(offset, cbfs.cbfs_offset)
        self.assertEqual(arch, cbfs.arch)
        return cbfs

    def _check_uboot(self, cbfs, ftype=cbfs_util.TYPE_RAW, offset=0x38,
                     data=U_BOOT_DATA, cbfs_offset=None):
        """Check that the U-Boot file is as expected

        Args:
            cbfs: CbfsReader object to check
            ftype: Expected file type
            offset: Expected offset of file
            data: Expected data in file
            cbfs_offset: Expected CBFS offset for file's data

        Returns:
            CbfsFile object containing the file
        """
        self.assertIn('u-boot', cbfs.files)
        cfile = cbfs.files['u-boot']
        self.assertEqual('u-boot', cfile.name)
        self.assertEqual(offset, cfile.offset)
        if cbfs_offset is not None:
            self.assertEqual(cbfs_offset, cfile.cbfs_offset)
        self.assertEqual(data, cfile.data)
        self.assertEqual(ftype, cfile.ftype)
        self.assertEqual(cbfs_util.COMPRESS_NONE, cfile.compress)
        self.assertEqual(len(data), cfile.memlen)
        return cfile

    def _check_dtb(self, cbfs, offset=0x38, data=U_BOOT_DTB_DATA,
                   cbfs_offset=None):
        """Check that the U-Boot dtb file is as expected

        Args:
            cbfs: CbfsReader object to check
            offset: Expected offset of file
            data: Expected data in file
            cbfs_offset: Expected CBFS offset for file's data
        """
        self.assertIn('u-boot-dtb', cbfs.files)
        cfile = cbfs.files['u-boot-dtb']
        self.assertEqual('u-boot-dtb', cfile.name)
        self.assertEqual(offset, cfile.offset)
        if cbfs_offset is not None:
            self.assertEqual(cbfs_offset, cfile.cbfs_offset)
        self.assertEqual(U_BOOT_DTB_DATA, cfile.data)
        self.assertEqual(cbfs_util.TYPE_RAW, cfile.ftype)
        self.assertEqual(cbfs_util.COMPRESS_NONE, cfile.compress)
        self.assertEqual(len(U_BOOT_DTB_DATA), cfile.memlen)

    def _check_raw(self, data, size, offset=0, arch=cbfs_util.ARCHITECTURE_X86):
        """Check that two raw files are added as expected

        Args:
            data: Data to check
            size: Expected ROM size
            offset: Expected offset to first CBFS file
            arch: Expected architecture
        """
        cbfs = self._check_hdr(data, size, offset=offset, arch=arch)
        self._check_uboot(cbfs)
        self._check_dtb(cbfs)

    def _get_expected_cbfs(self, size, arch='x86', compress=None, base=None):
        """Get the file created by cbfstool for a particular scenario

        Args:
            size: Size of the CBFS in bytes
            arch: Architecture of the CBFS, as a string
            compress: Compression to use, e.g. cbfs_util.COMPRESS_LZMA
            base: Base address of file, or None to put it anywhere

        Returns:
            Resulting CBFS file, or None if cbfstool is not available
        """
        if not self.have_cbfstool or not self.have_lz4:
            return None
        cbfs_fname = os.path.join(self._indir, 'test.cbfs')
        cbfs_util.cbfstool(cbfs_fname, 'create', '-m', arch, '-s', '%#x' % size)
        if base:
            base = [(1 << 32) - size + b for b in base]
        cbfs_util.cbfstool(cbfs_fname, 'add', '-n', 'u-boot', '-t', 'raw',
                           '-c', compress and compress[0] or 'none',
                           '-f', tools.GetInputFilename(
                               compress and 'compress' or 'u-boot.bin'),
                           base=base[0] if base else None)
        cbfs_util.cbfstool(cbfs_fname, 'add', '-n', 'u-boot-dtb', '-t', 'raw',
                           '-c', compress and compress[1] or 'none',
                           '-f', tools.GetInputFilename(
                               compress and 'compress' or 'u-boot.dtb'),
                           base=base[1] if base else None)
        return cbfs_fname

    def _compare_expected_cbfs(self, data, cbfstool_fname):
        """Compare against what cbfstool creates

        This compares what binman creates with what cbfstool creates for what
        is proportedly the same thing.

        Args:
            data: CBFS created by binman
            cbfstool_fname: CBFS created by cbfstool
        """
        if not self.have_cbfstool or not self.have_lz4:
            return
        expect = tools.ReadFile(cbfstool_fname)
        if expect != data:
            tools.WriteFile('/tmp/expect', expect)
            tools.WriteFile('/tmp/actual', data)
            print('diff -y <(xxd -g1 /tmp/expect) <(xxd -g1 /tmp/actual) | colordiff')
            self.fail('cbfstool produced a different result')

    def test_cbfs_functions(self):
        """Test global functions of cbfs_util"""
        self.assertEqual(cbfs_util.ARCHITECTURE_X86, cbfs_util.find_arch('x86'))
        self.assertIsNone(cbfs_util.find_arch('bad-arch'))

        self.assertEqual(cbfs_util.COMPRESS_LZMA, cbfs_util.find_compress('lzma'))
        self.assertIsNone(cbfs_util.find_compress('bad-comp'))

    def test_cbfstool_failure(self):
        """Test failure to run cbfstool"""
        if not self.have_cbfstool:
            self.skipTest('No cbfstool available')
        try:
            # In verbose mode this test fails since stderr is not captured. Fix
            # this by turning off verbosity.
            old_verbose = cbfs_util.VERBOSE
            cbfs_util.VERBOSE = False
            with test_util.capture_sys_output() as (_stdout, stderr):
                with self.assertRaises(Exception) as e:
                    cbfs_util.cbfstool('missing-file', 'bad-command')
        finally:
            cbfs_util.VERBOSE = old_verbose
        self.assertIn('Unknown command', stderr.getvalue())
        self.assertIn('Failed to run', str(e.exception))

    def test_cbfs_raw(self):
        """Test base handling of a Coreboot Filesystem (CBFS)"""
        size = 0xb0
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA)
        data = cbw.get_data()
        self._check_raw(data, size)
        cbfs_fname = self._get_expected_cbfs(size=size)
        self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_invalid_file_type(self):
        """Check handling of an invalid file type when outputiing a CBFS"""
        size = 0xb0
        cbw = CbfsWriter(size)
        cfile = cbw.add_file_raw('u-boot', U_BOOT_DATA)

        # Change the type manually before generating the CBFS, and make sure
        # that the generator complains
        cfile.ftype = 0xff
        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('Unknown type 0xff when writing', str(e.exception))

    def test_cbfs_invalid_file_type_on_read(self):
        """Check handling of an invalid file type when reading the CBFS"""
        size = 0xb0
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)

        data = cbw.get_data()

        # Read in the first file header
        cbr = cbfs_util.CbfsReader(data, read=False)
        with io.BytesIO(data) as fd:
            self.assertTrue(cbr._find_and_read_header(fd, len(data)))
            pos = fd.tell()
            hdr_data = fd.read(cbfs_util.FILE_HEADER_LEN)
            magic, size, ftype, attr, offset = struct.unpack(
                cbfs_util.FILE_HEADER_FORMAT, hdr_data)

        # Create a new CBFS with a change to the file type
        ftype = 0xff
        newdata = data[:pos]
        newdata += struct.pack(cbfs_util.FILE_HEADER_FORMAT, magic, size, ftype,
                               attr, offset)
        newdata += data[pos + cbfs_util.FILE_HEADER_LEN:]

        # Read in this CBFS and make sure that the reader complains
        with self.assertRaises(ValueError) as e:
            cbfs_util.CbfsReader(newdata)
        self.assertIn('Unknown type 0xff when reading', str(e.exception))

    def test_cbfs_no_space(self):
        """Check handling of running out of space in the CBFS"""
        size = 0x60
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('No space for header', str(e.exception))

    def test_cbfs_no_space_skip(self):
        """Check handling of running out of space in CBFS with file header"""
        size = 0x5c
        cbw = CbfsWriter(size, arch=cbfs_util.ARCHITECTURE_PPC64)
        cbw._add_fileheader = True
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('No space for data before offset', str(e.exception))

    def test_cbfs_no_space_pad(self):
        """Check handling of running out of space in CBFS with file header"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw._add_fileheader = True
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('No space for data before pad offset', str(e.exception))

    def test_cbfs_bad_header_ptr(self):
        """Check handling of a bad master-header pointer"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        data = cbw.get_data()

        # Add one to the pointer to make it invalid
        newdata = data[:-4] + struct.pack('<I', cbw._header_offset + 1)

        # We should still be able to find the master header by searching
        with test_util.capture_sys_output() as (stdout, _stderr):
            cbfs = cbfs_util.CbfsReader(newdata)
        self.assertIn('Relative offset seems wrong', stdout.getvalue())
        self.assertIn('u-boot', cbfs.files)
        self.assertEqual(size, cbfs.rom_size)

    def test_cbfs_bad_header(self):
        """Check handling of a bad master header"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        data = cbw.get_data()

        # Drop most of the header and try reading the modified CBFS
        newdata = data[:cbw._header_offset + 4]

        with test_util.capture_sys_output() as (stdout, _stderr):
            with self.assertRaises(ValueError) as e:
                cbfs_util.CbfsReader(newdata)
        self.assertIn('Relative offset seems wrong', stdout.getvalue())
        self.assertIn('Cannot find master header', str(e.exception))

    def test_cbfs_bad_file_header(self):
        """Check handling of a bad file header"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        data = cbw.get_data()

        # Read in the CBFS master header (only), then stop
        cbr = cbfs_util.CbfsReader(data, read=False)
        with io.BytesIO(data) as fd:
            self.assertTrue(cbr._find_and_read_header(fd, len(data)))
            pos = fd.tell()

        # Remove all but 4 bytes of the file headerm and try to read the file
        newdata = data[:pos + 4]
        with test_util.capture_sys_output() as (stdout, _stderr):
            with io.BytesIO(newdata) as fd:
                fd.seek(pos)
                self.assertEqual(False, cbr._read_next_file(fd))
        self.assertIn('File header at 0x0 ran out of data', stdout.getvalue())

    def test_cbfs_bad_file_string(self):
        """Check handling of an incomplete filename string"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw.add_file_raw('16-characters xx', U_BOOT_DATA)
        data = cbw.get_data()

        # Read in the CBFS master header (only), then stop
        cbr = cbfs_util.CbfsReader(data, read=False)
        with io.BytesIO(data) as fd:
            self.assertTrue(cbr._find_and_read_header(fd, len(data)))
            pos = fd.tell()

        # Create a new CBFS with only the first 16 bytes of the file name, then
        # try to read the file
        newdata = data[:pos + cbfs_util.FILE_HEADER_LEN + 16]
        with test_util.capture_sys_output() as (stdout, _stderr):
            with io.BytesIO(newdata) as fd:
                fd.seek(pos)
                self.assertEqual(False, cbr._read_next_file(fd))
        self.assertIn('String at %#x ran out of data' %
                      cbfs_util.FILE_HEADER_LEN, stdout.getvalue())

    def test_cbfs_debug(self):
        """Check debug output"""
        size = 0x70
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        data = cbw.get_data()

        try:
            cbfs_util.DEBUG = True
            with test_util.capture_sys_output() as (stdout, _stderr):
                cbfs_util.CbfsReader(data)
            self.assertEqual('name u-boot\ndata %s\n' % U_BOOT_DATA,
                             stdout.getvalue())
        finally:
            cbfs_util.DEBUG = False

    def test_cbfs_bad_attribute(self):
        """Check handling of bad attribute tag"""
        if not self.have_lz4:
            self.skipTest('lz4 --no-frame-crc not available')
        size = 0x140
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', COMPRESS_DATA, None,
                         compress=cbfs_util.COMPRESS_LZ4)
        data = cbw.get_data()

        # Search the CBFS for the expected compression tag
        with io.BytesIO(data) as fd:
            while True:
                pos = fd.tell()
                tag, = struct.unpack('>I', fd.read(4))
                if tag == cbfs_util.FILE_ATTR_TAG_COMPRESSION:
                    break

        # Create a new CBFS with the tag changed to something invalid
        newdata = data[:pos] + struct.pack('>I', 0x123) + data[pos + 4:]
        with test_util.capture_sys_output() as (stdout, _stderr):
            cbfs_util.CbfsReader(newdata)
        self.assertEqual('Unknown attribute tag 123\n', stdout.getvalue())

    def test_cbfs_missing_attribute(self):
        """Check handling of an incomplete attribute tag"""
        if not self.have_lz4:
            self.skipTest('lz4 --no-frame-crc not available')
        size = 0x140
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', COMPRESS_DATA, None,
                         compress=cbfs_util.COMPRESS_LZ4)
        data = cbw.get_data()

        # Read in the CBFS master header (only), then stop
        cbr = cbfs_util.CbfsReader(data, read=False)
        with io.BytesIO(data) as fd:
            self.assertTrue(cbr._find_and_read_header(fd, len(data)))
            pos = fd.tell()

        # Create a new CBFS with only the first 4 bytes of the compression tag,
        # then try to read the file
        tag_pos = pos + cbfs_util.FILE_HEADER_LEN + cbfs_util.FILENAME_ALIGN
        newdata = data[:tag_pos + 4]
        with test_util.capture_sys_output() as (stdout, _stderr):
            with io.BytesIO(newdata) as fd:
                fd.seek(pos)
                self.assertEqual(False, cbr._read_next_file(fd))
        self.assertIn('Attribute tag at %x ran out of data' % tag_pos,
                      stdout.getvalue())

    def test_cbfs_file_master_header(self):
        """Check handling of a file containing a master header"""
        size = 0x100
        cbw = CbfsWriter(size)
        cbw._add_fileheader = True
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        data = cbw.get_data()

        cbr = cbfs_util.CbfsReader(data)
        self.assertIn('u-boot', cbr.files)
        self.assertEqual(size, cbr.rom_size)

    def test_cbfs_arch(self):
        """Test on non-x86 architecture"""
        size = 0x100
        cbw = CbfsWriter(size, arch=cbfs_util.ARCHITECTURE_PPC64)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA)
        data = cbw.get_data()
        self._check_raw(data, size, offset=0x40,
                        arch=cbfs_util.ARCHITECTURE_PPC64)

        # Compare against what cbfstool creates
        cbfs_fname = self._get_expected_cbfs(size=size, arch='ppc64')
        self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_stage(self):
        """Tests handling of a Coreboot Filesystem (CBFS)"""
        if not elf.ELF_TOOLS:
            self.skipTest('Python elftools not available')
        elf_fname = os.path.join(self._indir, 'cbfs-stage.elf')
        elf.MakeElf(elf_fname, U_BOOT_DATA, U_BOOT_DTB_DATA)

        size = 0xb0
        cbw = CbfsWriter(size)
        cbw.add_file_stage('u-boot', tools.ReadFile(elf_fname))

        data = cbw.get_data()
        cbfs = self._check_hdr(data, size)
        load = 0xfef20000
        entry = load + 2

        cfile = self._check_uboot(cbfs, cbfs_util.TYPE_STAGE, offset=0x28,
                                  data=U_BOOT_DATA + U_BOOT_DTB_DATA)

        self.assertEqual(entry, cfile.entry)
        self.assertEqual(load, cfile.load)
        self.assertEqual(len(U_BOOT_DATA) + len(U_BOOT_DTB_DATA),
                         cfile.data_len)

        # Compare against what cbfstool creates
        if self.have_cbfstool:
            cbfs_fname = os.path.join(self._indir, 'test.cbfs')
            cbfs_util.cbfstool(cbfs_fname, 'create', '-m', 'x86', '-s',
                               '%#x' % size)
            cbfs_util.cbfstool(cbfs_fname, 'add-stage', '-n', 'u-boot',
                               '-f', elf_fname)
            self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_raw_compress(self):
        """Test base handling of compressing raw files"""
        if not self.have_lz4:
            self.skipTest('lz4 --no-frame-crc not available')
        size = 0x140
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', COMPRESS_DATA, None,
                         compress=cbfs_util.COMPRESS_LZ4)
        cbw.add_file_raw('u-boot-dtb', COMPRESS_DATA, None,
                         compress=cbfs_util.COMPRESS_LZMA)
        data = cbw.get_data()

        cbfs = self._check_hdr(data, size)
        self.assertIn('u-boot', cbfs.files)
        cfile = cbfs.files['u-boot']
        self.assertEqual(cfile.name, 'u-boot')
        self.assertEqual(cfile.offset, 56)
        self.assertEqual(cfile.data, COMPRESS_DATA)
        self.assertEqual(cfile.ftype, cbfs_util.TYPE_RAW)
        self.assertEqual(cfile.compress, cbfs_util.COMPRESS_LZ4)
        self.assertEqual(cfile.memlen, len(COMPRESS_DATA))

        self.assertIn('u-boot-dtb', cbfs.files)
        cfile = cbfs.files['u-boot-dtb']
        self.assertEqual(cfile.name, 'u-boot-dtb')
        self.assertEqual(cfile.offset, 56)
        self.assertEqual(cfile.data, COMPRESS_DATA)
        self.assertEqual(cfile.ftype, cbfs_util.TYPE_RAW)
        self.assertEqual(cfile.compress, cbfs_util.COMPRESS_LZMA)
        self.assertEqual(cfile.memlen, len(COMPRESS_DATA))

        cbfs_fname = self._get_expected_cbfs(size=size, compress=['lz4', 'lzma'])
        self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_raw_space(self):
        """Test files with unused space in the CBFS"""
        size = 0xf0
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA)
        data = cbw.get_data()
        self._check_raw(data, size)
        cbfs_fname = self._get_expected_cbfs(size=size)
        self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_offset(self):
        """Test a CBFS with files at particular offsets"""
        size = 0x200
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA, 0x40)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA, 0x140)

        data = cbw.get_data()
        cbfs = self._check_hdr(data, size)
        self._check_uboot(cbfs, ftype=cbfs_util.TYPE_RAW, offset=0x40,
                          cbfs_offset=0x40)
        self._check_dtb(cbfs, offset=0x40, cbfs_offset=0x140)

        cbfs_fname = self._get_expected_cbfs(size=size, base=(0x40, 0x140))
        self._compare_expected_cbfs(data, cbfs_fname)

    def test_cbfs_invalid_file_type_header(self):
        """Check handling of an invalid file type when outputting a header"""
        size = 0xb0
        cbw = CbfsWriter(size)
        cfile = cbw.add_file_raw('u-boot', U_BOOT_DATA, 0)

        # Change the type manually before generating the CBFS, and make sure
        # that the generator complains
        cfile.ftype = 0xff
        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('Unknown file type 0xff', str(e.exception))

    def test_cbfs_offset_conflict(self):
        """Test a CBFS with files that want to overlap"""
        size = 0x200
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA, 0x40)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA, 0x80)

        with self.assertRaises(ValueError) as e:
            cbw.get_data()
        self.assertIn('No space for data before pad offset', str(e.exception))

    def test_cbfs_check_offset(self):
        """Test that we can discover the offset of a file after writing it"""
        size = 0xb0
        cbw = CbfsWriter(size)
        cbw.add_file_raw('u-boot', U_BOOT_DATA)
        cbw.add_file_raw('u-boot-dtb', U_BOOT_DTB_DATA)
        data = cbw.get_data()

        cbfs = cbfs_util.CbfsReader(data)
        self.assertEqual(0x38, cbfs.files['u-boot'].cbfs_offset)
        self.assertEqual(0x78, cbfs.files['u-boot-dtb'].cbfs_offset)


if __name__ == '__main__':
    unittest.main()