Open Stack

     Having spent some time last week writing code for openstack-common, 
and having spent yet more time trying to get those changes into Nova, I 
think it would be useful to define some best practices when crossing the 
boundary between common and other openstack projects.

Background:

     The openstack-common project is subject to a standard code-review 
process (and, soon, will also have Jenkins testing gates.)  Sadly, 
patches that are merged into openstack-common are essentially orphans.  
Bringing those changes into actual use requires yet another step, a 
'merge from common' patch where the code changes in common are copied 
into a specific project (e.g. nova.)
     Merge-from-common patches are generated via an automated process.  
Specific projects express dependencies on specific common components via 
a config file, e.g. 'nova/openstack-common.conf'.  The actual file copy 
is performed by 'openstack-common/update.py,' and its behavior is 
governed by the appropriate openstack-common.conf file.

Questions:

     When should changes from common be merged into other projects?
     What should a 'merge-from-common' patch look like?
     What code-review standards should core committers observe when 
reviewing merge-from-common patches?

Proposals:

I.      As soon as a patch drops into common, the patch author should 
submit merge-from-common patches to all affected projects.
     A.  (This should really be done by a bot, but that's not going to 
happen overnight)

II.     In the event that I. is not observed, merge-from-common patches 
will contain bits from multiple precursor patches.  That is not only OK, 
but encouraged.
     A.  Keeping projects in sync with common is important!
     B.  Asking producers of merge-from-common patches to understand the 
full diff will discourage the generation of such merges.

III.    Merge-from-common patches should be the product of a single 
unedited run of update.py.
     A.  If a merge-from-common patch breaks pep8 or a test in nova, 
don't fix the patch; fix the code in common.

IV.    Merge-from-common patches are 'presumed justified'.  That means:
     A. Reviewers of merge-from-common patches should consider test 
failures and pep8 breakages, and obvious functional problems.
     B. Reviewers of merge-from-common patches should not consider the 
usefulness, design, etc. of merge-from-common patches.  Such concerns 
need to be handled within the common review process.
     C. Merges from common should get reviewed early and approved 
readily in order to avoid project divergence

V.     Changes to openstack-common.conf are a special case.
     A. Patches with openstack-common.conf changes should include the 
relevant merge-from-common changes.
     B. Such patches should /not/ include any other merge-from-common 
changes.
     C. Such patches should not only include the common merges, but 
should also include whatever code changes make use of the new merge.
     D. Such patches require the same justification and scrutiny as any 
other standard project patch.

Please discuss!  If we're able to reach general agreement about this 
process, I will document the process in the openstack-common HACKING 
guidelines.

-Andrew




On 7/2/12 11:38 AM, Russell Bryant (Code Review) wrote:
> I did that before seeing this patch.  However, I think I prefer what I pushed since it's individual updates explaining what they update instead of a blanket "update everything" commit.
>
>