Date: Mon, 24 Feb 2014 18:31:08 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Jordan Hubbard <jordan.hubbard@gmail.com> Cc: freebsd-filesystems@freebsd.org, freebsd-hackers@freebsd.org, Willem Jan Withagen <wjw@digiware.nl>, Perry Hutchison <perryh@pluto.rain.com> Subject: Re: Thoughts on Multi-Symlink Concept Message-ID: <alpine.BSF.2.00.1402241828000.61905@fledge.watson.org> In-Reply-To: <43505B61-FAE8-4A61-922E-78F6007BBFC3@gmail.com> References: <CAO2cuEMC==HstC4VkkiFpHyo6LA_xyCjYKvCEECXneVLNnZpZg@mail.gmail.com> <A31B3F88-861F-459B-AD67-F146D5514594@mail.turbofuzz.com> <530049a1.XXZ1PjZFgRyCu9X6%perryh@pluto.rain.com> <53092D83.6050603@digiware.nl> <43505B61-FAE8-4A61-922E-78F6007BBFC3@gmail.com>
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On Sat, 22 Feb 2014, Jordan Hubbard wrote: >> Yes, please can we get these .... >> >> Apollo Domain systems had those, and they were great. Set SYSTYPE to BSD4 >> and get the BSD tree and all that came with it, or SYSV to get the other >> stuff. > > Yep, I loved these things on Domain/OS! We system admin types used them to > do all kinds of clever (and useful) things. > > Looks like FreeBSD has actually *had* an implementation for 6 years now. I > don’t necessarily agree with the architectural decision to create a > different namespace and command (varsym) to manipulate it - it was really > nice just having it be a part of the standard environ(7) - but hey, any > implementation is better than no implementation. Whatever happened to > https://wiki.freebsd.org/200808DevSummit?action=AttachFile&do=get&target=variant-symlinks-for-freebsd.pdf > ? Some care is required here: at least one of the past implementations floating around had the neat property that user-defined symlink expansions occurred before system-defined ones, even for setuid binaries. This allowed trivial replacement of libraries out from under a binary, making rooting boxes easy. I'm actually a fan of variant symlinks as well, having used them in AFS -- I'd just prefer we aim for a model that minimises inconvenient rooting of boxes. (I'm not passing judgement on this particular patch, mind you.) I believe Brooks Davis did the last serious pass at variant symlinks and might opine further on the topic. Robert From owner-freebsd-hackers@FreeBSD.ORG Mon Feb 24 18:37:53 2014 Return-Path: <owner-freebsd-hackers@FreeBSD.ORG> Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id EB91B26C; Mon, 24 Feb 2014 18:37:53 +0000 (UTC) Received: from co9outboundpool.messaging.microsoft.com (co9ehsobe002.messaging.microsoft.com [207.46.163.25]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 93B931780; Mon, 24 Feb 2014 18:37:52 +0000 (UTC) Received: from mail44-co9-R.bigfish.com (10.236.132.237) by CO9EHSOBE023.bigfish.com (10.236.130.86) with Microsoft SMTP Server id 14.1.225.22; Mon, 24 Feb 2014 18:37:45 +0000 Received: from mail44-co9 (localhost [127.0.0.1]) by mail44-co9-R.bigfish.com (Postfix) with ESMTP id B9566C803E6; Mon, 24 Feb 2014 18:37:45 +0000 (UTC) X-Forefront-Antispam-Report: CIP:157.56.240.101; 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DIR:OUT; SFP:1101; SCL:1; SRVR:BY2PR05MB775; H:BY2PR05MB582.namprd05.prod.outlook.com; CLIP:66.129.241.12; FPR:BCC1D6DC.AEDA7D16.32F5BD7B.4EF1D94B.20382; PTR:InfoNoRecords; A:1; MX:1; LANG:en; Received: from mail44-co9 (localhost.localdomain [127.0.0.1]) by mail44-co9 (MessageSwitch) id 1393267063714704_3014; Mon, 24 Feb 2014 18:37:43 +0000 (UTC) Received: from CO9EHSMHS005.bigfish.com (unknown [10.236.132.250]) by mail44-co9.bigfish.com (Postfix) with ESMTP id A8B2B8C0047; Mon, 24 Feb 2014 18:37:43 +0000 (UTC) Received: from BL2PRD0510HT001.namprd05.prod.outlook.com (157.56.240.101) by CO9EHSMHS005.bigfish.com (10.236.130.15) with Microsoft SMTP Server (TLS) id 14.16.227.3; Mon, 24 Feb 2014 18:37:43 +0000 Received: from BY2PR05MB775.namprd05.prod.outlook.com (10.141.224.152) by BL2PRD0510HT001.namprd05.prod.outlook.com (10.255.100.36) with Microsoft SMTP Server (TLS) id 14.16.411.0; Mon, 24 Feb 2014 18:37:42 +0000 Received: from BY2PR05MB582.namprd05.prod.outlook.com (10.141.219.146) by BY2PR05MB775.namprd05.prod.outlook.com (10.141.224.152) with Microsoft SMTP Server (TLS) id 15.0.883.10; Mon, 24 Feb 2014 18:37:40 +0000 Received: from BY2PR05MB582.namprd05.prod.outlook.com ([10.141.219.146]) by BY2PR05MB582.namprd05.prod.outlook.com ([10.141.219.146]) with mapi id 15.00.0883.010; Mon, 24 Feb 2014 18:37:40 +0000 From: Andrew Duane <aduane@juniper.net> To: Robert Watson <rwatson@freebsd.org>, Jordan Hubbard <jordan.hubbard@gmail.com> Subject: RE: Thoughts on Multi-Symlink Concept Thread-Topic: Thoughts on Multi-Symlink Concept Thread-Index: AQHPMCLWAfcQ8HrO+ky5HMi/vn1+QZrEvQ4sgAAA7RA= Date: Mon, 24 Feb 2014 18:37:39 +0000 Message-ID: <c95138a571f141878d75a60e54f4f38c@BY2PR05MB582.namprd05.prod.outlook.com> References: <CAO2cuEMC==HstC4VkkiFpHyo6LA_xyCjYKvCEECXneVLNnZpZg@mail.gmail.com> <A31B3F88-861F-459B-AD67-F146D5514594@mail.turbofuzz.com> <530049a1.XXZ1PjZFgRyCu9X6%perryh@pluto.rain.com> <53092D83.6050603@digiware.nl> <43505B61-FAE8-4A61-922E-78F6007BBFC3@gmail.com> <alpine.BSF.2.00.1402241828000.61905@fledge.watson.org> In-Reply-To: <alpine.BSF.2.00.1402241828000.61905@fledge.watson.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [66.129.241.12] x-forefront-prvs: 0132C558ED Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: juniper.net X-FOPE-CONNECTOR: Id%0$Dn%*$RO%0$TLS%0$FQDN%$TlsDn% Cc: "freebsd-filesystems@freebsd.org" <freebsd-filesystems@freebsd.org>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Willem Jan Withagen <wjw@digiware.nl>, Perry Hutchison <perryh@pluto.rain.com> X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Technical Discussions relating to FreeBSD <freebsd-hackers.freebsd.org> List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-hackers>, <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe> List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>; List-Post: <mailto:freebsd-hackers@freebsd.org> List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help> List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe> X-List-Received-Date: Mon, 24 Feb 2014 18:37:54 -0000 -----Original Message----- From: owner-freebsd-hackers@freebsd.org [mailto:owner-freebsd-hackers@freeb= sd.org] On Behalf Of Robert Watson Sent: Monday, February 24, 2014 1:31 PM To: Jordan Hubbard Cc: freebsd-filesystems@freebsd.org; freebsd-hackers@freebsd.org; Willem Ja= n Withagen; Perry Hutchison Subject: Re: Thoughts on Multi-Symlink Concept On Sat, 22 Feb 2014, Jordan Hubbard wrote: >>> Apollo Domain systems had those, and they were great. Set SYSTYPE to BS= D4=20 >>> and get the BSD tree and all that came with it, or SYSV to get the othe= r=20 >.> stuff. >> >> Yep, I loved these things on Domain/OS! We system admin types used them= to=20 >> do all kinds of clever (and useful) things. >> >> Looks like FreeBSD has actually *had* an implementation for 6 years now.= I=20 >> don't necessarily agree with the architectural decision to create a=20 >> different namespace and command (varsym) to manipulate it - it was reall= y=20 >> nice just having it be a part of the standard environ(7) - but hey, any= =20 >> implementation is better than no implementation. Whatever happened to=20 >> https://wiki.freebsd.org/200808DevSummit?action=3DAttachFile&do=3Dget&ta= rget=3Dvariant-symlinks-for-freebsd.pdf? > >Some care is required here: at least one of the past implementations float= ing=20 >around had the neat property that user-defined symlink expansions occurred= =20 >before system-defined ones, even for setuid binaries. This allowed trivia= l=20 >replacement of libraries out from under a binary, making rooting boxes eas= y.=20 >I'm actually a fan of variant symlinks as well, having used them in AFS --= I'd=20 >just prefer we aim for a model that minimises inconvenient rooting of boxe= s.=20 >(I'm not passing judgement on this particular patch, mind you.) I believe= =20 >Brooks Davis did the last serious pass at variant symlinks and might opine= =20 >further on the topic. > >Robert I'd also be careful of violating the Principle of Least Astonishment with a= ny Implementation. Multi or Variable symlnks that suddenly change meaning Can really confound people. /Andrew
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