[RFC] Suggested "combined tree" for easier development and Franky integration.

[Stefan (metze) Metzmacher]

Kai Blin schrieb:
> Hi folks,
> 
> 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
> COPYING
> docs-xml/
> examples/
> MAINTAINERS
> Manifest
> packaging/
> pcp/
> PFIF.txt
> Read-Manifest-Now
> README
> README.Coding
> release-scripts/
> Roadmap
> source/
> swat/
> testsuite/
> WHATSNEW.txt
> 
> The Samba4 tree looks like this:
> kai at blackjack:~/samba/samba4$ ls -1p
> BUGS.txt
> COPYING
> howto.txt
> NEWS
> packaging/
> PFIF.txt
> prog_guide.txt
> source/
> swat/
> swat2.txt
> testdata/
> testprogs/
> TODO
> WHATSNEW.txt
> 
> 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
> BUGS.txt
> COPYING
> docs-xml/
> examples/
> howto.txt
> MAINTAINERS
> Manifest
> merged_branches.txt
> pcp/
> PFIF.txt
> prog_guide.txt
> Read-Manifest-Now
> README
> README.Coding
> release-scripts/
> Roadmap
> source3/
> source4/
> swat/
> testdata/
> testprogs/
> testsuite/
> TODO
> 
> 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 [1].
> 
> 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 [2]
> 
> 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.

I like the concept, but let us (me) redo the git-filter-branch thing so
that each new commit has a reference to the old sha1 in it.

metze


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 252 bytes
Desc: OpenPGP digital signature
Url : http://lists.samba.org/archive/samba-technical/attachments/20080905/497b6337/signature.bin