FYI: SVN to GIT converter currently broken, github is falling behind

Ulrich Spörlein uqs at
Fri Dec 4 18:49:07 UTC 2015

2015-11-08 12:06 GMT+01:00 Ulrich Spörlein <uqs at>:
> 2015-11-08 11:32 GMT+01:00 Ulrich Spörlein <uqs at>:
>> 2015-11-08 2:51 GMT+01:00 Alfred Perlstein <alfred at>:
>>> Uli,
>>> One of the biggest concerns I've heard from folks using FreeBSD's git mirror
>>> is that the hashes can change.
>>> I have a question about this.   Is it possible to keep track of what the
>>> "official" git mirror (on github) is doing and keep that as a log.  Then
>>> that log can be used to replay commits when there is a divergence problem.
>>> What I'm basically saying is that let's take this small example:
>>> importer is working fine @rev 10000
>>> imports 10000
>>> imports 10001
>>> imports 10002
>>> something happens to importer to give indeterminate shas.
>>> imports 10003 - sha is "unstable" sha3
>>> imports 10004 - sha is "unstable" sha4
>>> imports 10005 - sha is "unstable" sha5
>>> imports 10006 - sha is "unstable" sha6
>>> importer is fixed
>>> At this point normally we'd rewind the importer to 10002 and then force
>>> update the affected branches.
>>> My question is... can the imports of 10003, 10004, 10005 and 10006 be put
>>> into the importer such that any "mirror site" that re-does the import using
>>> the most up to date importer will get the same shas.
>>> That would allow to proceed with 10007, etc without force pushing.
>>> This should be possible based on querying "git" for the meta data associated
>>> with sha3..sha6 and then forcing those commits to have the same meta data.
>>> This would eliminate the concern about shas in the mirror changing that I've
>>> heard.
>> The goal of the conversion is that everyone can re-do the conversion
>> in their basement and come up with the same history and checksums.
>> This was not the case when I first started, as there was some
>> non-deterministic hash structure being used in svn2git. This was fixed
>> in the code and then all converter runs produced the very same
>> results.
>> The scenario that we have right now, is that one of the merge commits
>> done about two weeks ago is being handled different by svn2git w/ svn
>> v1.8 vs. svn v1.9 and I haven't investigated yet how the API's
>> behavior changed to cause this. I'm afraid I also swapped out all my
>> knowledge about svn2git internals and will have to redo this all from
>> scratch :/
>> Your suggestion could only work, if we hard-code this svn revision
>> special handling into svn2git, either in the code or by providing more
>> mappings and rules to the process. svn2git should run hermetic and not
>> poke at github's commits to see how things were handled in the past.
>> It has to be self-sufficient and must not depend on github.
>> This would also only work, if the "breakage" window was very small,
>> but it is already about two weeks long and will surely increase till I
>> find the proper fix.
>> So, to take a stand here: this sort of kludge is unlikely to ever
>> happen. Git commit hashes *might* change in the future. I really don't
>> see how this is a big deal anyway.  It happened once and I'm trying to
>> have it never happen again. But why are people afraid of this
>> happening? Every "official" git commit is tagged with a SVN revision
>> and the contents of those revisions are obviously correct (just not
>> the ancestry and the commit objects, possibly). So it would be easy to
>> write a script that replays VendorA's git history and swaps out the
>> new official commits for the old official commits. There would be no
>> merge conflicts.
>> I can see how this would be annoying if you have 100 developers and
>> dozens of branches that are far from mainline FreeBSD. But I'm sure
>> these companies that depend on git will come forward and donate some
>> of their developer manpower to help me with keeping the converter
>> stable/deterministic. Right? Right? :) :)
>> Cheers,
>> Uli
> Quick update: doc is so far unaffected by svn 1.9, but for ports, the
> drift happened as of Jul 18, so you'd need to special case a lot of
> commits.
> Here's the same commit, and the difference between 1.8 and 1.9:
> % git cat-file commit 803795d
> tree 7fc83aba022834da5c218114b09ad4640735bcc0
> parent c96fb0418e545a569b5975b4d878a30a948c29d5
> author olgeni <olgeni at> 1437203525 +0000
> committer olgeni <olgeni at> 1437203525 +0000
> Upgrade to version 0.4.1.
> % git cat-file commit 61ca43b
> tree 7fc83aba022834da5c218114b09ad4640735bcc0
> parent c96fb0418e545a569b5975b4d878a30a948c29d5
> author olgeni <olgeni at> 1437203529 +0000
> committer olgeni <olgeni at> 1437203529 +0000
> Upgrade to version 0.4.1.
> In case you don't see it, there's a 4s difference in the timestamps
> for authoring and committing. Here's the original:
> % svn log -vc392405 svn://
> ------------------------------------------------------------------------
> r392405 | olgeni | 2015-07-18 09:12:05 +0200 (Sat, 18 Jul 2015) | 2 lines
> Changed paths:
>    M /head/www/elixir-maru/Makefile
>    M /head/www/elixir-maru/distinfo
> Upgrade to version 0.4.1.
> ------------------------------------------------------------------------
> So yeah, svn 1.9 returned a timestamp that was off by 4s. WTF?
> For base it's actually even more complicated than I had thought so
> far. But let's take this one step at time ...

An update, which you won't like to hear:

SVN v1.9 is totally innocent, the API changed a little and has been
patched, this is not the source of the difference between the
currently published repo and a clean run. The difference stems from
the fact that the svnsync'ed copy on was poisoned and
is *NOT* in sync with our main repo. People tell me this is due to a
shortcoming of svnsync that can race and thus produce different
metadata for a commit, depending on when it is run.

This is a clusterfuck.

Both freebsd-base and freebsd-ports are no longer reproducible by
third-parties. It is only a matter of time when freebsd-doc is

clusteradm@ sadly has remained rather silent on this issue and unless
we can move the mirroring to rsync or syncthing or whatever I don't
see how the project can continue to provide a so-called git "mirror"


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