build: Make setup.py run from srcdir to avoid distutils errors

src/python-lxc/setup.py.in

@@ -22,15 +22,36 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
 # USA
 
+import os, os.path
 from distutils.core import setup, Extension
 
-module = Extension('_lxc', sources=['@srcdir@/lxc.c'],
-                   include_dirs=['@top_builddir@/src', '@top_srcdir@/src'],
-                   library_dirs=['@top_builddir@/src/lxc'], libraries=['lxc'])
+# Distutils doesn't cope well with source files that have relative paths going
+# up in the directory tree: it tries to navigate outside of the build dir and
+# fails miserably. Therefore, we will instead cd to the source directory,
+# run this script from there, but write the build products to the correct path.
+#
+# Since we will be changing directories before building, we must transform
+# all the path variables to their forms relative to srcdir.
+
+srcdir, builddir, top_srcdir, top_builddir = map(os.path.abspath,
+    ["@srcdir@", "@builddir@", "@top_srcdir@", "@top_builddir@"])
+
+builddir, top_srcdir, top_builddir = map(lambda d: os.path.relpath(d, srcdir),
+    [builddir, top_srcdir, top_builddir])
+
+os.chdir(srcdir)
+
+module = Extension('_lxc', sources=['lxc.c'],
+                   include_dirs=[os.path.join(top_srcdir, 'src'),
+                                 os.path.join(top_builddir, 'src')],
+                   library_dirs=[os.path.join(top_builddir, 'src/lxc')],
+                   libraries=['lxc'])
+
 
 setup(name='_lxc',
       version='0.1',
       description='LXC',
       packages=['lxc'],
-      package_dir={'lxc': '@srcdir@/lxc'},
-      ext_modules=[module])
+      package_dir={'lxc': 'lxc'},
+      ext_modules=[module],
+      options={'build': {'build_base': os.path.join(builddir, 'build')}})