Add flashrom memory layout detection by FMAP (using fmap_decode)

Add flashrom memory layout detection by FMAP (using fmap_decode)

To support arbitrary memory layout in the future, we need to support
fmap_decode.

Before starting using / testing:
(1) you must have fmap_decode ( http://code.google.com/p/flashmap/ ) installed and in PATH.
    on systems without fmap_decode, flashrom_util will fallback to internal layout.
(2) you must have a BIOS firmware image with FMAP. (most recent images already have that - you can execute fmap_decode FILENAME to check)

To use it <flashrom_util>:
Add an extra image (flashrom image content, usually read  by flashrom_util::read_whole() ) parameter when you call flashrom_util::detect_*_layout.
If fmap_decode is found in system PATH and the image does have fmap, flashrom_util will use its layout instead.

To use it <FlashromUtility>:
No need to change anything. FlashromUtility will try to use fmap_decode if it's available. 

To verify / test:
 image = open(firmware_filename).read()
 <base test>
  # check the if the output offset/names are the same by compile_layout / decode_fmap_layout to same image.
  print compile_layout(DEFAULT_CHROMEOS_FIRMWARE_LAYOUT_DESCRIPTIONS['bios'], len(image))
  print decode_fmap_layout(DEFAULT_CHROMEOS_FMAP_CONVERTION, image)

 <integrated test>
  # without image, only internal layout is used.
  print flashrom.detect_chromeos_bios_layout(len(image))
  # with image, fmap will be tried.
  print flashrom.detect_chromeos_bios_layout(len(image), image)

BUG=chrome-os-partner:920
TEST=manual

Change-Id: I810a3a3ac8885ff4ac245c77d5b0ea8bcaec86de

[vb, 2010-08-27 15:11:28]

Hung-Te, can you please enhance the CL description a bit,
explaining how this modification has been tested and how it
is supposed to be used.

[Hung-Te, 2010-08-27 16:31:52]

sorry - the CL desc is now improved.

[vb, 2010-08-27 17:04:01]

LGTM

Thank you for writing a good description. One question below I will leave to
your discretion (you might want to consult style guide also).

http://codereview.chromium.org/3246002/diff/3001/4001
File client/common_lib/flashrom_util.py (right):

http://codereview.chromium.org/3246002/diff/3001/4001#newcode379
client/common_lib/flashrom_util.py:379: def detect_layout(self,
layout_desciption, size=None, image=None):
here and below, why are you specifying default parameter values when invoking
this function? wouldn't it be better readable if default parameters were not
mentioned?

[Hung-Te, 2010-08-30 10:40:00]

Added a python version of FMAP decoder from latest flashmap project.

Also refined the test files so that size/image are no longer default parameters
in flashrom_util.

http://codereview.chromium.org/3246002/diff/3001/4001
File client/common_lib/flashrom_util.py (right):

http://codereview.chromium.org/3246002/diff/3001/4001#newcode379
client/common_lib/flashrom_util.py:379: def detect_layout(self,
layout_desciption, size=None, image=None):
Basically for backward compatibility... Since most existing tests in autotest do
not trust/use the FMAP structure carried in image, adding default parameter here
helps migrating the source, so only those who wants FMAP to work can explicitly
provide the image.

But just like your comments and the style guilde suggested, it would be more
meaningful to remove the defaults so that users can address the different
behaviors. I will fix them later.