[RFC] Suggested "combined tree" for easier development and Franky
kai at samba.org
Fri Sep 5 15:17:14 GMT 2008
at the last Franky meeting, we realized that our current attempt at creating a
combined Samba3/Samba4 build using git submodules was clumsy and fragile.
So we came up with a combined tree solution to address this issue.
Incidentally, this combined tree might be useful before we get the integrated
build sorted out already.
There is a small one-time effort involved migrating personal branches over,
more about that below. Let me first explain how the merged tree looks like.
As you all know, the Samba3 tree looks like this:
kai at blackjack:~/samba/samba3$ ls -1p
The Samba4 tree looks like this:
kai at blackjack:~/samba/samba4$ ls -1p
Now, it's obvious that a plain merge of these directories isn't possible as
there is a couple of clashes. Some of those are easy to fix (COPYING and
PFIF.txt), some are hard (source/).
As trying to combine the Samba3 and Samba4 source/ folder into a single folder
would be madness, we decided to merge the Samba3 source/ folder as source3/
and merge the Samba4 source/ folder as source4/. For my proof of concept
merge, I dropped the other conflicting files that weren't identical and as a
result, the combined tree looks like this:
kai at blackjack:~/samba/samba-devel$ ls -1p
The nice part about this is that nothing really changed for building Samba3 or
Samba4 standalone, just that to e.g. build Samba4, you now do "cd
source4; ./configure; make" instead of "cd source; ./configure; make".
So far so good, our first attempt looked pretty much like this. However, git's
tracking of file renames is very basic and breaks down if a lot of files are
renamed. For both Sambas, source is big enough to break. So while history
wasn't lost completely (e.g. git blame path/to/file still worked), git log
path/to/file didn't work anymore. The Git folks think this is a minor
annoyance, Volker hated it, and I tend to agree with Volker. There's a couple
of workarounds, but they were all pretty clumsy.
In the end, we found a solution that preserved the history across the merge
for a small one-time migration effort. Using some fancy git magic (git
filter-branch, in case you're interested), Volker created a Samba3 branch
that had all commits since the beginning use "source3/" instead of "source/",
and then repeated the same for a Samba4 branch. I then merged those two
branches using some more git magic Jelmer and I had discovered on Wednesday
(I'll describe the whole process in another email for people interested in
this) and uploaded the combined branches to git.samba.org .
Now, because we changed the commit objects doing this, the sha1-sums of the
commit objects don't work anymore, meaning git rebase or similar will blow up
attempting to rebase on the new, unknown objects. However, it's easy to work
around this with little effort, described on the Franky wiki page 
So while I don't propose to go live with this setup right now, I'm hoping for
some feedback on the general approach. The incredible advantage of this is
that (Franky considerations aside) code that is shared between Samba3 and
Samba4 can be pulled out of the source3/4 dirs and needs to be updated only
once instead of twice. So even though this looks like "yet one more branch"
right now, it will mean less branches to check things in in the long and even
in the medium term. Also, instead of having to get a separate Samba4 branch
to run smbtorture tests with Samba3, you just need to build source4 once, and
not change the repo.
We need to discuss how to handle the remaining duplicates from the old Samba3
and Samba4 trees. I'm looking forward to suggestions on how to improve the
migration guide as well.
 Check out the combined tree at git://git.samba.org/kai/samba/franky.git
 The migration guide is at
WorldForge developer http://www.worldforge.org/
Wine developer http://wiki.winehq.org/KaiBlin
Samba team member http://www.samba.org/samba/team/
Will code for cotton.
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