how to access pysam internals from external cython project

ex.pyx

from pysam.libcalignmentfile cimport AlignmentFile

cdef AlignmentFile samfile = AlignmentFile("../normal.bam", "rb")

print samfile.reference_filename
print samfile.b == NULL

setup.py

from distutils.core import setup
from distutils.extension import Extension
import Cython
from Cython.Build import cythonize

setup(
      cmdclass={'build_ext': Cython.Build.build_ext},
      ext_modules = [Extension("ex",
                               ["ex.pyx"],
                               language='c',
                               libraries=["z", "hts"],
                               include_dirs=["/home/brentp/src/pysam/pysam",
                                   "/usr/include"],
                               )]
)