En Thu, 26 Nov 2009 22:59:29 -0300, mercado <python.de...@gmail.com>
escribió:
Hello,
I am writing a Python program to read the Master Boot Record (MBR),
and I'm having trouble because I have no previous experience reading
binary files.
First off, I've written a binary file containing the MBR to disk using
the following command:
sudo dd if=/dev/sda of=/tmp/mbrcontent bs=1 count=512
Then I want to read the MBR file and parse out its information. For
example, I know that bytes 454-457 contain the address of the first
sector of the first partition, and bytes 458-461 contain the number of
sectors in the first partition (see
http://en.wikipedia.org/wiki/Master_boot_record for more information
on the structure of the MBR).
So far what I have is this:
--------------------------------------------------------------------------------
f = open("/tmp/mbrcontent", "rb")
contents = f.read()
f.close()
firstSectorAddress = contents[454:458]
numSectors = contents[458:462]
--------------------------------------------------------------------------------
On my machine, the bytes contained in firstSectorAddress are
"\x3F\x00\x00\x00", and the bytes contained in numSectors are
"\x20\x1F\x80\x01". I know from doing a pen and paper calculation
that the first sector address is 63, and the number of sectors is
25,173,792 (the numbers are stored in little-endian format).
How do I figure that out programmatically? I think that I can use
struct.unpack() to do this, but I'm not quite sure how to use it.
Can anybody help me out? Thanks in advance.
You're almost done:
py> import struct
py> firstSectorAddress = "\x3F\x00\x00\x00"
py> struct.unpack("<L", firstSectorAddress)
(63,)
py> struct.unpack("<L", "\x20\x1F\x80\x01")
(25173792,)
--
Gabriel Genellina
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