From mboxrd@z Thu Jan 1 00:00:00 1970 From: PJ Weisberg Subject: Re: Does content provenance matter? Date: Mon, 7 May 2012 15:14:25 -0700 Message-ID: References: <878vh4flh1.fsf@thomas.inf.ethz.ch> <1336427003.53220.YahooMailClassic@web121504.mail.ne1.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Thomas Rast , git@vger.kernel.org To: Kelly Dean X-From: git-owner@vger.kernel.org Tue May 08 00:14:31 2012 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1SRWCM-0004eC-QO for gcvg-git-2@plane.gmane.org; Tue, 08 May 2012 00:14:31 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756818Ab2EGWO0 convert rfc822-to-quoted-printable (ORCPT ); Mon, 7 May 2012 18:14:26 -0400 Received: from mail-vb0-f46.google.com ([209.85.212.46]:38227 "EHLO mail-vb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752760Ab2EGWOZ convert rfc822-to-8bit (ORCPT ); Mon, 7 May 2012 18:14:25 -0400 Received: by vbbff1 with SMTP id ff1so1242756vbb.19 for ; Mon, 07 May 2012 15:14:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=cWn3FwhE26XmuuJc1eVXLXJF65KBx7CRRAvdX88pECg=; b=DAeZ/238IwxHMKsoTsuLA28lCznRqli+zcvAtJnTuJnapRPh+Xzgj1rKrMA5TvS9wE jkDZ22yFASj2Bwf7j3haQZsZSYWVN+Td5IzsySHFivuSB/KCM1eh81dFbAUBW+WlqSDv eWdFtclsnDMFJ+UIaShn5tb8XMjmADB9kcvgV1+A14+apgtZSVeM5Id9nIuqVS9eSrx1 vpHpL3XAjUBGgPtDHyypJdMahbmSiV2Y5bvI0xXsQYJ+6xu+XQ1pNQBRRkn5GvVxtHrW OHfrxFZS2ItusI+lJo79+zlUI2hE7lpsahpZ6qiPitOA3fawlMOzn5vYUU52fDXvQMpA OhIQ== Received: by 10.52.172.194 with SMTP id be2mr2293775vdc.60.1336428865210; Mon, 07 May 2012 15:14:25 -0700 (PDT) Received: by 10.220.118.206 with HTTP; Mon, 7 May 2012 15:14:25 -0700 (PDT) In-Reply-To: <1336427003.53220.YahooMailClassic@web121504.mail.ne1.yahoo.com> X-Google-Sender-Auth: BFkAXfsxx94n7qp8cZomNE6zXeI Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Mon, May 7, 2012 at 2:43 PM, Kelly Dean wrot= e: > --- On Mon, 5/7/12, Thomas Rast wrote: >> What's the difference between the following series of >> commits? >> >> =A0 Foo >> =A0 Bar >> =A0 Revert Bar >> >> and >> >> =A0 Foo >> >> You claim that they're the same, because the tree state >> after each is >> the same. =A0But I learned that Bar was broken, and >> recorded it for all to see. > No, I don't claim they're the same. Different commits have different = timestamps (and different commit messages, but that's not useful for au= tomatic searching to find which commits are derived from which others).= Consider if "Revert Bar" and "Bar" didn't point to their parents; coul= d you still deduce from them that Bar was broken? Yes--on the basis of = the commit timestamps (which shows their temporal order) and the conten= ts of the trees which the commits point to (which shows that Revert Bar= undoes a change made in Bar). But there could be any number of unrelated commits newer than "Bar" but older than "Revert Bar" on other branches. Even if you could trust the timestamps to be accurate (you can't), you still can't determine a commit's parent unambiguously. -PJ Gehm's Corollary to Clark's Law: Any technology distinguishable from magic is insufficiently advanced.