From owner-freebsd-hackers@FreeBSD.ORG Mon Apr 21 23:15:35 2014 Return-Path: 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 E0292FEF for ; Mon, 21 Apr 2014 23:15:35 +0000 (UTC) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "funkthat.com", Issuer "funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id BE35D14E1 for ; Mon, 21 Apr 2014 23:15:35 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id s3LNFYAd080923 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 21 Apr 2014 16:15:35 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id s3LNFYws080922; Mon, 21 Apr 2014 16:15:34 -0700 (PDT) (envelope-from jmg) Date: Mon, 21 Apr 2014 16:15:34 -0700 From: John-Mark Gurney To: Chris Torek Subject: Re: MAXPHYS in md(4) Message-ID: <20140421231534.GY43976@funkthat.com> Mail-Followup-To: Chris Torek , freebsd-hackers@freebsd.org References: <20140421222210.GW43976@funkthat.com> <201404212230.s3LMUWif045734@elf.torek.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201404212230.s3LMUWif045734@elf.torek.net> User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Mon, 21 Apr 2014 16:15:35 -0700 (PDT) Cc: freebsd-hackers@freebsd.org X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Apr 2014 23:15:35 -0000 Chris Torek wrote this message on Mon, Apr 21, 2014 at 16:30 -0600: > >This really should be moved up into the generic GEOM layer so geom > >module ever sees IO that is larger than MAXPHYS... > > Well, maybe, but if you're going to do something like that it > might be nice to have the device equivalent of MTU discovery.... Why? GEOM modules are written on the assumption that no IO larger than MAXPHYS will ever be seen... They allocate arrays of structures or other items based upon MAXPHYS, and will smash the stack/crash//do bad things if it receives an IO larger than MAXPHYS... The change would not break anything that isn't already broken (or working by luck)... Now if you're talking about wanting to increase MAXPHYS, there are many threads talking about what needs to be done about it, but that is completely different than this issue... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."