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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 91500C54FCB for ; Mon, 27 Apr 2020 18:33:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70AAC21D79 for ; Mon, 27 Apr 2020 18:33:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588012415; bh=Kvl1vZC9kDd1F7eq2SkykbjVcxFidxJg+IWcZRfXVAo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=JSkmasO9aHx7hnLiEzqzC1gGq5b4AOWzs9WlFFkStNdFKI9awTd35o4RWiPii7KOE T/oV2IM7p0wh5DTaJBvI2ZlnJbf03MqENS+vbexyOq43owbWPLvuVRIzocBMVyPB4e 9qsVHozf/x+dbsmB80hl/cw6RcB9yHR8x1XXYIiI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726572AbgD0Sdf (ORCPT ); Mon, 27 Apr 2020 14:33:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:47972 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726295AbgD0Sde (ORCPT ); Mon, 27 Apr 2020 14:33:34 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C91E3205C9; Mon, 27 Apr 2020 18:33:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588012412; bh=Kvl1vZC9kDd1F7eq2SkykbjVcxFidxJg+IWcZRfXVAo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=vTUbWzE5YKsAhGIfXoRp6hDQedTaAGNp8/huMp2MGwjrnBnIXHcBAq0/WY8QdQVWP 3fwbk784z3Nv1x9AHPRORRmxK1OEK6hOa6dlldVISf/+5WX+j/LhXOW/uH1RlqCgSk CTNRshvUm2K2Rpl2z+NivnJNaxfo+daK65RoGEYo= Date: Mon, 27 Apr 2020 11:33:31 -0700 From: Andrew Morton To: Vlastimil Babka Cc: Luis Chamberlain , Kees Cook , Iurii Zaikin , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , Michal Hocko , David Rientjes , Matthew Wilcox , "Eric W . Biederman" , "Guilherme G . Piccoli" , Alexey Dobriyan , Thomas Gleixner , Greg Kroah-Hartman , Christian Brauner , Masami Hiramatsu , Michal Hocko Subject: Re: [PATCH v3 1/5] kernel/sysctl: support setting sysctl parameters from kernel command line Message-Id: <20200427113331.f0c1e8e7cee98644260448d3@linux-foundation.org> In-Reply-To: <20200427180433.7029-2-vbabka@suse.cz> References: <20200427180433.7029-1-vbabka@suse.cz> <20200427180433.7029-2-vbabka@suse.cz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 27 Apr 2020 20:04:29 +0200 Vlastimil Babka wrote: > A recently proposed patch to add vm_swappiness command line parameter in > addition to existing sysctl [1] made me wonder why we don't have a general > support for passing sysctl parameters via command line. Googling found only > somebody else wondering the same [2], but I haven't found any prior discussion > with reasons why not to do this. > > Settings the vm_swappiness issue aside (the underlying issue might be solved in > a different way), quick search of kernel-parameters.txt shows there are already > some that exist as both sysctl and kernel parameter - hung_task_panic, > nmi_watchdog, numa_zonelist_order, traceoff_on_warning. A general mechanism > would remove the need to add more of those one-offs and might be handy in > situations where configuration by e.g. /etc/sysctl.d/ is impractical. > > Hence, this patch adds a new parse_args() pass that looks for parameters > prefixed by 'sysctl.' and tries to interpret them as writes to the > corresponding sys/ files using an temporary in-kernel procfs mount. This > mechanism was suggested by Eric W. Biederman [3], as it handles all dynamically > registered sysctl tables, even though we don't handle modular sysctls. Errors > due to e.g. invalid parameter name or value are reported in the kernel log. > > The processing is hooked right before the init process is loaded, as some > handlers might be more complicated than simple setters and might need some > subsystems to be initialized. At the moment the init process can be started and > eventually execute a process writing to /proc/sys/ then it should be also fine > to do that from the kernel. > > Sysctls registered later on module load time are not set by this mechanism - > it's expected that in such scenarios, setting sysctl values from userspace is > practical enough. > > ... > > + sysctl.*= [KNL] > + Set a sysctl parameter, right before loading the init > + process, as if the value was written to the respective > + /proc/sys/... file. Both '.' and '/' are recognized as > + separators. Unrecognized parameters and invalid values > + are reported in the kernel log. Sysctls registered > + later by a loaded module cannot be set this way. > + Example: sysctl.vm.swappiness=40 Why support "."? I think only supporting "/" is perfectly adequate and simplifies documentation. It aligns the command-line syntax with the rest of the sysctl documentation. I'm not seeing the need to provide two ways of doing the same thing?