From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02A01C4360C for ; Tue, 8 Oct 2019 09:18:39 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CA47E20673 for ; Tue, 8 Oct 2019 09:18:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CA47E20673 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52760 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iHldc-00076h-Sp for qemu-devel@archiver.kernel.org; Tue, 08 Oct 2019 05:18:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34456) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iHlaL-0004od-0U for qemu-devel@nongnu.org; Tue, 08 Oct 2019 05:15:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iHlaJ-0006Di-6g for qemu-devel@nongnu.org; Tue, 08 Oct 2019 05:15:12 -0400 Received: from 10.mo69.mail-out.ovh.net ([46.105.73.241]:48668) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iHlaJ-0006Ak-01 for qemu-devel@nongnu.org; Tue, 08 Oct 2019 05:15:11 -0400 Received: from player692.ha.ovh.net (unknown [10.108.54.97]) by mo69.mail-out.ovh.net (Postfix) with ESMTP id 29B4C6BD13 for ; Tue, 8 Oct 2019 11:15:07 +0200 (CEST) Received: from kaod.org (lns-bzn-46-82-253-208-248.adsl.proxad.net [82.253.208.248]) (Authenticated sender: groug@kaod.org) by player692.ha.ovh.net (Postfix) with ESMTPSA id 24905A923CBF; Tue, 8 Oct 2019 09:15:01 +0000 (UTC) Date: Tue, 8 Oct 2019 11:14:59 +0200 From: Greg Kurz To: Christian Schoenebeck Subject: Re: [Qemu-devel] [PATCH v7 0/3] 9p: Fix file ID collisions Message-ID: <20191008111459.048e659f@bahia.lan> In-Reply-To: <1590425.yRI6RxI3rl@silver> References: <7439377.rdf1oF7g69@silver> <20190923185012.06131248@bahia.lan> <1590425.yRI6RxI3rl@silver> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Ovh-Tracer-Id: 6024408926595815744 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedufedrheelgdduhecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmd X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 46.105.73.241 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stefan Hajnoczi , "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" , qemu-devel@nongnu.org, Antonios Motakis , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 24 Sep 2019 11:31:06 +0200 Christian Schoenebeck wrote: > On Montag, 23. September 2019 18:50:12 CEST Greg Kurz wrote: > > > > > If yes, and since that would mean I was the only person ever having > > > > > tested > > > > > the actual fix, shouldn't --multidevs=remap|forbid better be marked as > > > > > experimental (docs and runtime warning) for now? Maybe that would also > > > > > anticipate receiving feedback from people actually using it later on. > > > > > > > > Makes sense. I don't think it is worth having a runtime warning, > > > > but I'll turn remap to x-remap and amend the docs. > > > > > > Mwa, I would like to veto against your "x-remap" plan though. Keep in mind > > > I also have to send out a patch for libvirt for this fix. Even I would > > > not have read "x" to stand for "experimental". So I would definitely > > > favor a runtime warning instead of renaming that parameter. > > > > Hmmm... I don't see the point in adding a warning for a feature that > > is only active if the user explicitly asks for it. > > Because many people might be using this option without ever reading the docs, > e.g. because of being suggested by copy & paste tutorials or any stack*.com > forum. > > > And, anyway, this > > still is an experimental feature, right ? > > No, it is not a feature. It is still a fix. :) I cannot use 9p without this > fix at all, so it is not some optional "feature" for me. > I understand your need but this is still arguable. The 9p device has a limitation with cross-device setups. The actual bug is to silently cause inode number collisions in the guest. This is partly fixed by the "9p: Treat multiple devices on one export as an error" patch. Thinking again, it would even make sense to move "remap" from "9p: Added virtfs option 'multidevs=remap|forbid|warn'" to its own patch. We could then consider that the bug is fully fixed with "multidevs=forbid|warn". Then comes the "remap" feature which is expected to lift the limitation with cross-device setups, with a "not yet determined" performance cost and light reviewing of the code. > x-remap would just make things unnecessarily more complicated without adding > anything useful. > Not really. This gives a crucial information to the user about the level of confidence we have in this feature. > A warning/info log could be used to motivate people providing feedback and > make them clearly aware about their current version still being an > experimental fix in their specific qemu version. That warning/info is just a > one line change that can easily be dropped at some point in future after this > qid fix proofed to be reliable (i.e. from users' feedback and test cases). > The overwhelming majority of feedbacks I had on 9p the last few years are CVEs. Antonios and you are the only users who ever seemed to care for cross-device setups. So I don't expect much feedback on that area and I don't buy the "motivate people" argument, especially since "remap" won't be the default. > > Not sure it is time to have > > libvirt to support it yet. > > Most people are using libvirt xml configs instead of calling qemu directly > with command line options. So of course I will suggest a libvirt patch as soon > as this patch set is pulled on qemu side. > Yes and before a feature has a chance to be officially supported in libvirt, people usually rely on the domain XML tag to pass extra arguments to QEMU. https://blog.vmsplice.net/2011/04/how-to-pass-qemu-command-line-options.html With the current fsdev implementation, we can only pass properties to the -fsdev command line option. So this would require to not use the XML tag and manually _open-code_ the needed QEMU arguments: And if fsdev is converted to be a proper QEMU device, it would as easy as: This is unrelated but it would also allow to drop a lot of code in fsdev that mimics what qdev would give us for free. :) > > Also, I strongly recommend you try out "virtio-fs" which is going to be soon the production grade way of sharing files between host and guest. https://www.mail-archive.com/libvir-list@redhat.com/msg182457.html Cheers, -- Greg