Hi,

I've been doing some work around making 'make distcheck' and VPATH
builds successful for VDSM.
Some patches have already been merged, but there is one that I've
abandoned because it touches a bigger issue.

When doing a VPATH build, some python sources are build-time generated
from '.py.in' files (at this moment: 'lib/vdsm/common/constants.py.in',
'lib/vdsm/common/config.py.in', 'lib/vdsm/common/dsaversion.py.in',
'/lib/sos/vdsm.py.in').

Suppose we do a VPATH build with:

cd ${SRCROOT} && \
     ./autogen.sh && \
     make distclean && \
     mkdir -p /tmp/ovirt-build && \
     cd /tmp/ovirt-build && \
     ${SRCROOT}/configure && \
     make

The build-generated '.py' files will land in '/tmp/ovirt-build/lib/...'.
As a result, even though the build-generated python modules and the
source ones refer to each other, they can't see each other.

After some trial and error here are my observations:
   - we can't generate resulting '.py' files in $(srcdir) - 'make
distcheck' purposely sets $(srcdir) to be read-only
   - we can't just simply add $(builddir) to PYTHONPATH - there are no
'__init__.py' files in $(builddir), so i.e. 'import vdsm.common.config'
will fail
   - we can't create dummy '__init__.py' files in $(builddir), because
that would break in-tree-builds (we would have to clean regular,
git-maintained files)

In conclusion, I think we would need to implement a custom python module
loader to make VPATH/distcheck successful. It would need to be
parametrized with $(builddir)'s path, and would try to resolve
unsuccessful imports by finding build-time generated files inside.

However, after looking at other oVirt projects (i.e. 'ioprocess',
'ovirt-iso-uploader', 'ovirt-node-ng', 'ovirt-register'), I can see that
most of them fail 'make distcheck'. They have even more severe
'makefile'-issues than importing build-time generated python files.

So the question is - do we really need 'make distcheck' for VDSM to suceed?

Marcin