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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09007C433FE for ; Thu, 3 Nov 2022 17:52:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231736AbiKCRwr (ORCPT ); Thu, 3 Nov 2022 13:52:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230473AbiKCRwq (ORCPT ); Thu, 3 Nov 2022 13:52:46 -0400 Received: from wout1-smtp.messagingengine.com (wout1-smtp.messagingengine.com [64.147.123.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 08E64B4E; Thu, 3 Nov 2022 10:52:45 -0700 (PDT) Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailout.west.internal (Postfix) with ESMTP id 461D93200805; Thu, 3 Nov 2022 13:52:43 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute4.internal (MEProxy); Thu, 03 Nov 2022 13:52:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:in-reply-to:message-id :mime-version:references:reply-to:sender:subject:subject:to:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm3; t=1667497962; x=1667584362; bh=/jl6iy49gLxL3OPiwyn4XeKNHfG6 xbi+bJ/ciZbyZA8=; b=QGP52SJRBMNSAg3g5OYqX4Egb+NRp6yOkpi+D2ZDl2jr quA3BWYUowucf+XGBHEAfQ58WFvh5hDpvnRqkT84mIgSI1/KL0z2E4Pm+mZqo1Ls Ot3s6pmaVI6OzFOmCaXVEdJysEN7mmW8g/xU7gutqJkCnZosDd3WGco/aP7m2JZR B9gVNoW8armmum6yRew1EUOxS8rKH+0C3yJ+Zst6JcU1eHrRbQ81JY+snyDf1qiL 7psccSKpzKAxBTFBfuKhqGFJE0OpUDttqWlkKblFWZG44Rcub944ABvFu4Po/TZi 7P6KZbY+alCJbaRjR2Q2TOOMRQCJqhFyjtsI2n0Zhw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvgedrudelgddutdduucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepkfguohcu ufgthhhimhhmvghluceoihguohhstghhsehiughoshgthhdrohhrgheqnecuggftrfgrth htvghrnhepvddufeevkeehueegfedtvdevfefgudeifeduieefgfelkeehgeelgeejjeeg gefhnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepih guohhstghhsehiughoshgthhdrohhrgh X-ME-Proxy: Feedback-ID: i494840e7:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 3 Nov 2022 13:52:40 -0400 (EDT) Date: Thu, 3 Nov 2022 19:52:31 +0200 From: Ido Schimmel To: Jakub Kicinski Cc: Roman Gushchin , Andrew Lunn , Andy Ren , netdev@vger.kernel.org, richardbgobert@gmail.com, davem@davemloft.net, wsa+renesas@sang-engineering.com, edumazet@google.com, petrm@nvidia.com, pabeni@redhat.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, David Ahern , Stephen Hemminger Subject: Re: [PATCH net-next v2] netconsole: Enable live renaming for network interfaces used by netconsole Message-ID: References: <20221102002420.2613004-1-andy.ren@getcruise.com> <20221101204006.75b46660@kernel.org> <20221102125418.272c4381@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221102125418.272c4381@kernel.org> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Nov 02, 2022 at 12:54:18PM -0700, Jakub Kicinski wrote: > On Wed, 2 Nov 2022 10:14:38 -0700 Roman Gushchin wrote: > > > Agreed. BTW I wonder if we really want to introduce a netconsole > > > specific uAPI for this or go ahead with something more general. > > > > Netconsole is a bit special because it brings an interface up very early. > > E.g. in our case without the netconsole the renaming is happening before > > the interface is brought up. > > > > I wonder if the netconsole-specific flag should allow renaming only once. > > > > > A sysctl for global "allow UP rename"? > > > > This will work for us, but I've no idea what it will break for other users > > and how to check it without actually trying to break :) And likely we won't > > learn about it for quite some time, asssuming they don't run net-next. > > Then again IFF_LIVE_RENAME_OK was added in 5.2 so quite a while back. > > > > We added the live renaming for failover a while back and there were > > > no reports of user space breaking as far as I know. So perhaps nobody > > > actually cares and we should allow renaming all interfaces while UP? > > > For backwards compat we can add a sysctl as mentioned or a rtnetlink > > > "I know what I'm doing" flag? > > > > > > Maybe print an info message into the logs for a few releases to aid > > > debug? > > > > > > IOW either there is a reason we don't allow rename while up, and > > > netconsole being bound to an interface is immaterial. Or there is > > > no reason and we should allow all. > > > > My understanding is that it's not an issue for the kernel, but might be > > an issue for some userspace apps which do not expect it. > > There are in-kernel notifier users which could cache the name on up / > down. But yes, the user space is the real worry. > > > If you prefer to go with the 'global sysctl' approach, how the path forward > > should look like? > > That's the question. The sysctl would really just be to cover our back > sides, and be able to tell the users "you opted in by setting that > sysctl, we didn't break backward compat". But practically speaking, > its a different entity that'd be flipping the sysctl (e.g. management > daemon) and different entity that'd be suffering (e.g. routing daemon). > So the sysctl doesn't actually help anyone :/ > > So maybe we should just risk it and wonder about workarounds once > complains surface, if they do. Like generate fake down/up events. > Or create some form of "don't allow live renames now" lock-like > thing a process could take. > > Adding a couple more CCs and if nobody screams at us I vote we just > remove the restriction instead of special casing. Tried looking at history.git to understand the reasoning behind this restriction. I guess it's because back then it was only possible via IOCTL and user space wouldn't be notified about such a change. Nowadays user space gets a notification regardless of the administrative state of the netdev (see rtnetlink_event()). At least in-kernel listeners to NETDEV_CHANGENAME do not seem to care if the netdev is administratively up or not. So, FWIW, the suggested approach sounds sane to me.