Date: Mon, 23 Sep 2019 23:09:39 +0200 From: =?UTF-8?Q?Ulrich_Sp=C3=B6rlein?= <uspoerlein@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Shawn Webb <shawn.webb@hardenedbsd.org>, freebsd-git@freebsd.org Subject: Re: Service disruption: git converter currently down Message-ID: <CAJ9axoRQQWB92Tv=w488HN74DU4HfdgGrqG3mgkTBTFzaoNEUQ@mail.gmail.com> In-Reply-To: <CANCZdfoXT4sBLUhsaBA0sr1Lf4RfyXpU7cyn97yyNui-Mp7YDg@mail.gmail.com> References: <CAJ9axoR41gM5BGzT-nPJqqjym1cPYv31dDUwXwi4wsApfDJW%2Bw@mail.gmail.com> <CAJ9axoToynYpF=ZdWdtn_CkkA2nVkgtckQSu%2BcMis1NOXgUdnA@mail.gmail.com> <CAJ9axoR2VXFo9_hx9Z1Qwgs7U-dkan56hrUKO9f7uN6Wpd15xQ@mail.gmail.com> <CAHevUJHwDet8pBdrE4SN3nuoAUgP-ixpCz9uOTdwbE31UDDsbA@mail.gmail.com> <CAJ9axoSVhmSkNS6S1zTiwK5F3uUM%2B-8D2478=irZMeTjNxpnfg@mail.gmail.com> <20190923183424.ebnghzf67mx56aom@mutt-hbsd> <CAJ9axoQ-g2Qa2Qnr%2BPOD63s8sTH2Gsi7Rh2VMcZzQF5dd_kBvA@mail.gmail.com> <CANCZdfoXT4sBLUhsaBA0sr1Lf4RfyXpU7cyn97yyNui-Mp7YDg@mail.gmail.com>
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Am Mo., 23. Sept. 2019 um 21:06 Uhr schrieb Warner Losh <imp@bsdimp.com>: > > > > On Mon, Sep 23, 2019, 8:42 PM Ulrich Sp=C3=B6rlein <uspoerlein@gmail.com>= wrote: >> >> Am Mo., 23. Sept. 2019 um 20:34 Uhr schrieb Shawn Webb >> <shawn.webb@hardenedbsd.org>: >> > >> > Hey Ulrich, >> > >> > I appreciate your hard work in maintaining the git mirror. Work like >> > this can sometimes go unthanked. I want to take a moment to show >> > appreciation for you and the FreeBSD project in maintaining the git >> > mirror. >> > >> > I do have a few concerns with what was stated in your email. I've >> > written my concerns inline. I hope this discussion is a positive one, >> > wherein upstream and downstream can effectively come to a conclusion. >> > >> > On Mon, Sep 23, 2019 at 08:16:25PM +0200, Ulrich Sp??rlein wrote: >> > > Am Mo., 23. Sept. 2019 um 19:51 Uhr schrieb Sean Chittenden >> > > <sean@chittenden.org>: >> > > >> >> > > >> Please note however, that more "garbage" metadata escaped from SV= N into >> > > >> github, meaning 3rd parties have a hard time re-running the conve= rsion and >> > > >> making sure that it matches SVN down to the metadata (i.e. timest= amps). >> > > >> >> > > >> Eventually, this will have to be re-rolled and a new "master" bra= nch will >> > > >> be force-pushed into github. There's no timeline for this yet. >> > > > >> > > > >> > > > Wait, what? Can you elaborate? >> > > > >> > > > Discussion of a force-push to github has occurred a few times and = been explicitly ruled out because most of our corporate citizens use github= to integrate changes from FreeBSD. Rerolling master was universally rejec= ted when we socialized wanting to do this due to the level of disruption th= is would cause. The feedback was that this would be a high-cost, low-value= operation. In the tradeoffs of purity vs pragmatism, pragmatism wins ever= y time (that is the FreeBSD way). >> > > > >> > > > -sc >> > > >> > > >> > > This is not just about pragmatism and the disruption it would cause = is >> > > vastly overblown by people who don't seem to know much about the git >> > > storage model. >> > > >> > > There *is* garbage metadata in the published version on github, ther= e >> > > *is* a disclaimer on https://wiki.freebsd.org/GitWorkflow since >> > > forever, and the cost of switching from 1 published branch to anothe= r >> > > is literally: >> > > >> > > - git diff origin/broken_master mybranch > mybranch.patch >> > > - git checkout -b fixed_branch origin/fixed_master >> > > - patch < mybranch.patch >> > >> > Such a workflow breaks historical accuracy. Instead of `git annotate` >> > showing the history properly, it's now based on an "epoch commit". >> > Sure such a commit brings the branch to a working condition, but at >> > the cost of history. >> >> Is there really that much value in having "git blame" work in that envir= onment? >> My mental model is of short-lived branches that get upstreamed, so I'm b= iased >> towards this not being all that big of a problem (for some at least). > > > Yes. There absolutely is. > >> > > >> > > It should also be possible to merge both broken and fixed master int= o >> > > your branch (at the exact same SVN revision in time) and then you ca= n >> > > follow fixed_master going forward. You'll schlepp around double the >> > > commit history, but not tree objects. >> > > If you want to retain history, you can upstream the changes prior to >> > > the switch >> > >> > I so wish that were possible for certain downstream projects. We're >> > unable to upstream the majority of our work. To argue "upstream your >> > work and you won't be affected" is to choose an argument that does not >> > reflect the reality of a growing portion of FreeBSD's downstream >> > consumers: the inability to work effectively with upstream. >> >> :/ >> >> I'm 80% sure that you can just merge both branches and things will be fi= ne >> (though the exact incantation will surely be black magic). I'd love to >> try this on >> an actual repo though, I don't have the time to craft some test repo to = verify >> this assumption, and then find out that other repos are different). > > > One might be able to do this, but this is really quite a lot to ask. I've= done a lot of git rebase in connection with qemu. The hard part us knowing= hash X is for rev r123 in branch 1, but hash Y In branch 2. Once you can a= utomate that, for various mappings, a script to rebase old to new becomes p= ossible which will lessen the impact, but not eliminate it. Hmm, I think that's the trivial part. All commits record the SVN revision in the notes after all. See: % git show commit 2e105280ca193f7bafe103652bb1249704ba25f6 (HEAD -> master) Author: bdrewery <bdrewery@FreeBSD.org> Date: 2015-10-15 20:46:34 +0000 Remove unneeded libg++ reference that came in with r267511 based on a removed comment. Sponsored by: EMC / Isilon Storage Division Notes: svn path=3D/head/; revision=3D289388 So all that is left is matching up 2 notes in 2 branches (or 2 tree objects in 2 branches, actually). What's the tree on a specific branch: % git log -1 --format=3D%T master 9c96d76028084fe6b8077292fc428388a22f07f0 Search for it on a different branch (using the same master here, I don't have a repo handy with 2 different but identical branches) % git rev-list master | while read hash; do case `git log -1 --format=3D%T $hash` in 9c96d76028084fe6b8077292fc428388a22f07f0) echo "found commit $hash also pointing to tree 9c96d76028084fe6b8077292fc428388a22f07f0";; esac; done found commit 2e105280ca193f7bafe103652bb1249704ba25f6 also pointing to tree 9c96d76028084fe6b8077292fc428388a22f07f0 Except you can probably write that quicker also, maybe just dump all commit =E2=86=92 tree mappings and do something with that. As I said, it should be straightforward as long as you know a thing or two about git. > >> Also, I'll be offline in the coming weeks, so don't expect immediate res= ponses >> from me going forward. I already had to spent most of my weekend to patc= h >> things up and had to cancel other plans. > > > I think it is safe to view this discussion as just don't force push yet a= s we are in no position to mitigate the large disruption this would cause. = If you aren't force pushing master, there is no time urgency to solve this. > > Finally, and most importantly, thank you for all your time and efforts he= re. They are much appreciated. Any quibbling over future plans shouldn't de= tract from that. > > Warner There will not be a surprise force push if I can help it. That's what I just sacrificed a weekend for, after all :( Should (!!) the project ever decide to abandon SVN, then I would suggest to roll that into a re-do of the conversion, and also only start the conversion with the first commit to SVN, because the cvs2svn conversion also has a bunch of garbage in there, and we should rather not claim that those commits actually every happened in the way and form they are currently recorded in SVN. hth Uli
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