Bulding and Running the VirtualBox SDK sample using COM, VC++

VirtualBox is Sun Microsystem's desktop virtualization software which allows you to do cool stuff like running Linux right inside Windows without having to repartition Windows or anything like that. They recently released 1.6 version allows you to run even Solaris (not OpenSolaris yet at the time of this writing) inside Windows. (They also support a bunch of other operating systems as hosts and guests).

Check it out - its a breeze to download and get a Linux (e.g. Knoppix) distro working within minutes. With USB support, you can even mount a pen-drive and save your files externally.

I was poring over the developer docs to what they exposed in terms of an API. Its pretty cool - Virtualbox allows access to its runtime using both web services (Apache Axis et. al.) as well as using the now almost defunct COM (component object model) technology . It also seems to support the cross-platform Mozilla XPCOM but I haven't looked at it yet.

Having worked with COM a lot prior to 2000, i was eager to try out the COM approach. The docs however disappoint immensely as it seems to assume that if you were someone truly interested in really taking that route, you would know what to do. Turned out, my COM was rusty and after some digging around for almost non-existent COM documentation/articles, I figured I wasn't linking in the interfaces file generated by VirtualBox.

Install VirtualBox if you already haven't. The SDK is present under \Sun\xVM VirtualBox\sdk\

Here is a gist of steps I took :

Visual C++

1. Fire up your favorite C++ compiler (I use the free VC++ 9.0 Express edition) and create a Win32 console project.
2. Add the sdk\samples\API\tstVBoxAPIWin.cpp.
3. Add sdk\include to the INCLUDE path.
4. Don't forget to also add sdk\lib\VirtualBox_i.c to your sources since this file contains all the generated COM interfaces for VirtualBox.
5. Add sdk\lib to your linker path .
6. Run a build.


CYGWIN (using gcc, mingw32)

1. Copy all source files i.e. (tstVBoxAPIWin.cpp, VirtualBox_i.c, VirtualBox.h) to a working directory.

2. gcc -c tstVBoxAPIWin.cpp VirtualBox_i.c

3. export LD_LIBRARY_PATH = c:\WINDOWS\system32

4. gcc -o vbox VirtualBox_i.o tstVBoxAPIWin.o -mno-cygwin -lole32 -loleaut32


The resultant executable when run, prints out all my virtual machines for the various guest OSes I run on my Windows Box.

Output :

Name: knoppix-on-xp
Name: LKB_ON_KNOPPIX
Name: open-solaris

Not much achieved but for me this is a cool way to get back into my COM programming days while tinkering with my favorite virtualization software. The install has a SDK reference that gives all gory details about the various interfaces exposed by the COM interface. Onto more tinkering .........


References :

• http://forums.virtualbox.org/viewtopic.php?t=6948

Writing a Python Extension with SWIG, GCC on Cygwin

UPDATE : Please see comments below this post - the latest version of SWIG appears to have made the "setup.py" step described below - redundant.

t seemed easy at first. Many books document it, several folks blog about it, articles have been written about it, but I didn't quite seem to get it right. Here are my steps and missteps in getting the python sample from the SWIG tutorial to work right on my machine with cygwin 1.5.25, gcc 3.4.4, swig 1.3.35, python 2.5 already installed.

1. Download the sample example.c from the SWIG Tutorial.

2. Get the interface file from the same location and save a local copy in your working directory as say sample.i.

3. Run the swig compiler on it using 'swig -python sample.i' to get the machine generated python extension - example_wrap.c

If you are past this step, you have swig properly installed on your computer. We will now use the python distools package to do the rest of the magic for us.

4. Create a setup.py file that contains all dependencies required to create the Python extension. This is the critical step ! Here is what mine looks like .

from distutils.core import setup, Extension

module1 = Extension('_example', sources=['example_wrap.c',

'example.c'])

setup (name = 'example',

version = '1.0',

description = 'Simple example from SWIG tutorial',

ext_modules = [module1])

Note the underscore (_) before the module name. This little mistake could trip you up completely and lead to errors from the build process such as :

"Cannot export initexample: symbol not defined"

Apparently SWIG requires that you use an "-" before your module name. Also note that the sources attribute lists the C program and the swig-generated C program. It is also possible to list only the swig interface file as in sources= 'example.i' and allow python to complete Step 3 from above. This did not work for me. It trips up the linking process at a later point. Why ? - I have no clue.


5. Run the Python distool to generate the extension . Note the use of "inplace". This is convenient when developing as it generates the .pyd file (Python extension) in the current working directory. You may remove this if you want it in a standard "build" directory.

python setup.py build_ext --compiler=mingw32 --inplace

NOTE: The '--compiler=mingw32' option is to force compilation using the mingw32 compiler. This can be automated as described here . The mingw compiler should have been installed if you kept the defaults while installing GCC on cygwin. You may also install it separately from here or running the cygwin installer again and choose the mingw option along with its dependencies.

If all goes well, you should see no errors and upon completion, find a file named '_example.pyd' in your working directory.

6. Install the extension by running "python setup.py install" . Alternately simply copy the _example.pyd file to your Python install (e.g. c:\Python25\Lib\site_packages) .

7. If you fire up IDLE and run '>> import example' , you'll probably see an import error . However if you type "import _example", it'll succeed. This is how SWIG generates your module. You probably don't want to use your module this way. The way to fix it is to look for a python file named "example.py" in your current working directory. Copy this file to the same location as above (e.g. c:\Python25\Lib\site_packages) .

8. >>> import example as e

9. >>> e.fact(5)
120

---

References :

Here are several links I read up to get this example working - my thanks to all those authors. I'll caution though that a lot of the hacks about using pexports etc. that you'll find on many of these web sites are unnecessary if you are using Python 2.5. The Python 2.5 distribution comes with the import library. On my machine this is C:\Python25\libs\libpython25.a.

• http://sebsauvage.net/python/mingw.html (Ignore Steps 2,3 if you are using Python 2.5


• http://www.swig.org/tutorial.html (The official SWIG tutorial - simple, but deceptively so, supposed to work like a charm, but I wouldn't be writing this if it did !)


• http://docs.python.org/inst/tweak-flags.html (Section 6.22 talks about use of distools and some information on building extensions with older versions of Python) .



• http://www.swig.org/Doc1.3/Python.html#Python_nn6 (The BEST document PERIOD I found on this subject- unfortunately the last one too !)



• http://www.dabeaz.com/cgi-bin/wiki.pl?SwigFaq/SharedLibraries (SWIG wiki entry on building shared libraries on different platforms



• http://www.swig.org/Doc1.1/HTML/Contents.html (SWIG Users Manual if you want to do any heavy lifting using SWIG)



• http://boodebr.org/main/python/build-windows-extensions#CFG_DISTUTILS (Cleared the clutter about Python 2.5 Vs the older versions. Also has an interesting discussion about using Mingw32 directly Vs gcc on cygwin).