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Date:      Fri, 30 May 2008 16:11:28 +0100 (BST)
From:      Robert Watson <rwatson@FreeBSD.org>
To:        Alexander Leidinger <Alexander@Leidinger.net>
Cc:        Maxim Sobolev <sobomax@FreeBSD.org>, src-committers@FreeBSD.org, d@delphij.net, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org, Daniel Eischen <deischen@FreeBSD.org>, Xin LI <delphij@FreeBSD.org>, re@FreeBSD.org, David Schultz <das@FreeBSD.org>
Subject:   Re: cvs commit: src/include string.h src/lib/libc/string	Makefile.inc memchr.3 memrchr.c src/sys/sys param.h
Message-ID:  <20080530161058.B85310@fledge.watson.org>
In-Reply-To: <20080530165827.89052ulp729ogzy8@webmail.leidinger.net>
References:  <200805272004.m4RK4SZt029194@repoman.freebsd.org> <483C7FF2.6000607@FreeBSD.org> <483C977F.20105@delphij.net> <20080528060333.GA4699@zim.MIT.EDU> <Pine.GSO.4.64.0805281049150.7240@sea.ntplx.net> <20080529084608.X39873@fledge.watson.org> <Pine.GSO.4.64.0805291106120.12774@sea.ntplx.net> <20080529162517.V3678@fledge.watson.org> <20080530165827.89052ulp729ogzy8@webmail.leidinger.net>

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On Fri, 30 May 2008, Alexander Leidinger wrote:

>>>> So, this is neither a vote for nor against a backout, but this is a 
>>>> general call to resist the conservative tendancy that says "don't MFC 
>>>> minor things" because, in macro, it has a significant drag effect on the 
>>>> MFC process that keeps RELENG branches maintainable.
>>> 
>>> Ok, but consider the prior email with kan about MFC's after an 8.0 
>>> release. Since you must be able to run 7.x binaries on 8.0, then you can't 
>>> MFC any symbol changes from 8.0+ back to 7.x.  The symbols are basically 
>>> frozen in 7.x after 8.0 is released.
>> 
>> Sounds like a bug.  :-)
>
> We have the possibility of this behavior even in older releases. Imagine a 
> 8.0 release and a 8.1 release before a 7.4 release. And let 8.1 have a 
> symbol which is not available in 8.0 (MF9). Now let's MFC this symbol to 
> 7-stable before 7.4. Boom, you can not run a 7.4 binary which uses this 
> symbol on 8.0.
>
> More or less it comes down to be careful about things to MFC (don't MFC 
> symbols to the second last branch).

I think everyone is fine with "you must be careful".  What I think some of us 
would be less fine with is "you can't do it at all".

Robert N M Watson
Computer Laboratory
University of Cambridge



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