From owner-freebsd-net@FreeBSD.ORG Fri Apr 24 18:23:10 2015 Return-Path: Delivered-To: freebsd-net@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 3D2DD1B6 for ; Fri, 24 Apr 2015 18:23:10 +0000 (UTC) Received: from gold.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "gold.funkthat.com", Issuer "gold.funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 1B0D31075 for ; Fri, 24 Apr 2015 18:23:09 +0000 (UTC) Received: from gold.funkthat.com (localhost [127.0.0.1]) by gold.funkthat.com (8.14.5/8.14.5) with ESMTP id t3OIN9CR016474 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 24 Apr 2015 11:23:09 -0700 (PDT) (envelope-from jmg@gold.funkthat.com) Received: (from jmg@localhost) by gold.funkthat.com (8.14.5/8.14.5/Submit) id t3OIN8g2016473; Fri, 24 Apr 2015 11:23:08 -0700 (PDT) (envelope-from jmg) Date: Fri, 24 Apr 2015 11:23:08 -0700 From: John-Mark Gurney To: freebsd-net@FreeBSD.org, Poul-Henning Kamp Subject: Re: should m_copyback possibly throw data away? Message-ID: <20150424182308.GK37063@funkthat.com> References: <20150424181158.GJ37063@funkthat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150424181158.GJ37063@funkthat.com> X-Operating-System: FreeBSD 9.1-PRERELEASE amd64 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? User-Agent: Mutt/1.5.21 (2010-09-15) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (gold.funkthat.com [127.0.0.1]); Fri, 24 Apr 2015 11:23:09 -0700 (PDT) X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 24 Apr 2015 18:23:10 -0000 John-Mark Gurney wrote this message on Fri, Apr 24, 2015 at 11:11 -0700: > I would also be fine w/ documenting this behavior, though I'm sure > it'd be surprising to many that you'd have to check to make sure your > data was properly copied. Should have reviewed the m_copyback function before sending this email... It gets worse.. If the m_get to extend it fails, there is no notification that your data didn't get copyied into the mbuf.. and no warning in the man page that this function is unsafe and may cause data loss... Comments? -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."