From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-5.2 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 936D22022D for ; Fri, 4 Nov 2016 20:49:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757315AbcKDUtN (ORCPT ); Fri, 4 Nov 2016 16:49:13 -0400 Received: from cloud.peff.net ([104.130.231.41]:38835 "EHLO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754066AbcKDUtM (ORCPT ); Fri, 4 Nov 2016 16:49:12 -0400 Received: (qmail 9050 invoked by uid 109); 4 Nov 2016 19:49:10 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.84) with SMTP; Fri, 04 Nov 2016 19:49:10 +0000 Received: (qmail 25891 invoked by uid 111); 4 Nov 2016 19:49:36 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.84) with SMTP; Fri, 04 Nov 2016 15:49:36 -0400 Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Fri, 04 Nov 2016 15:49:07 -0400 Date: Fri, 4 Nov 2016 15:49:07 -0400 From: Jeff King To: Jacob Keller Cc: Junio C Hamano , Josh Triplett , Git mailing list Subject: Re: Regarding "git log" on "git series" metadata Message-ID: <20161104194907.3yxu2rkayfyic4dr@sigill.intra.peff.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Nov 04, 2016 at 12:19:55PM -0700, Jacob Keller wrote: > I agree with your assessment here. The main difficulty in implementing > gitrefs is to ensure that they actually do get picked up by > reachability checks to prevent dropping commits. I'm not sure how easy > this is, but I would much rather we go this route rather than > continuing along with the hack. This seems like the ideal solution, > since it solves the entire problem and doesn't need more hacks bolted > on. I think the main complication is that the reachability rules are used during object transfer. So you'd probably want to introduce some protocol extension to say "I understand gitrefs", so that when one side says "I have sha1 X and its reachable objects", we know whether they are including gitrefs there. And likewise receivers with transfer.fsckObjects may complain about the new gitref tree mode (fortunately a new object type shouldn't be needed). You might also want fallback rules for storing gitrefs on "old" servers (e.g., backfilling gitrefs you need if the server didn't them in the initial fetch). But I guess storing any gitrefs on such a server is inherently dangerous, because the server might prune them at any time. So perhaps a related question is: how can gitrefs be designed such that existing servers reject them (rather than accepting the push and then later throwing away half the data). It would be easy to notice in the client during a push that we are sending gitrefs to a server which does not claim that capability. But it seems more robust if it is the server who decides "I will not accept these bogus objects". I haven't thought all that hard about this. That's just my initial thoughts on what sound hard. Tweaking the reachability code doesn't seem all that bad; we already know all of the spots that care about S_ISGITLINK(). It may even be that some of those spots work out of the box (because gitlinks are usually about telling the graph-walking code that we _don't_ care about reachability; we do by default for trees and blobs). I'd be surprised if all such sites work out of the box, though. Even if they see "ah, sha1 X is referenced by tree Y and isn't a gitlink, and therefore should be reachable", they need to also note that "X" is a commit and recursively walk its objects. -Peff