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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 343A5C43331 for ; Sun, 10 Nov 2019 10:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD8B920869 for ; Sun, 10 Nov 2019 10:09:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=onstation.org header.i=@onstation.org header.b="DZzvnqcN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726681AbfKJKJP (ORCPT ); Sun, 10 Nov 2019 05:09:15 -0500 Received: from onstation.org ([52.200.56.107]:40598 "EHLO onstation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726609AbfKJKJO (ORCPT ); Sun, 10 Nov 2019 05:09:14 -0500 Received: from localhost (c-98-239-145-235.hsd1.wv.comcast.net [98.239.145.235]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: masneyb) by onstation.org (Postfix) with ESMTPSA id E3F2B3E953; Sun, 10 Nov 2019 10:09:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=onstation.org; s=default; t=1573380554; bh=tZRQ63Y3L1MwJPdKlkwcnVT/yKu4ORB6C4tSAe1YhkY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DZzvnqcN6fru0pg4LVSvX5YZ/MRTw8jUQg8DfOjutNhK6VvhSdWQhbIjnCPl+jB1R XbmP8Bc3OxPWJL2HHTFVhzug/FI43ej6hMU7amAoJsX0ZYgWR2gLVS5norh9glQitv fENBU9WHvc1Qvex6KFRWjgXdv1bO0Yqgk5zPtHqI= Date: Sun, 10 Nov 2019 05:09:13 -0500 From: Brian Masney To: Greg KH Cc: Alexey Dobriyan , pbonzini@redhat.com, linux-kernel@vger.kernel.org Subject: Re: "statsfs" API design Message-ID: <20191110100913.GA5064@onstation.org> References: <20191109184441.GA5092@avx2> <20191110091435.GC1435668@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191110091435.GC1435668@kroah.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 10, 2019 at 10:14:35AM +0100, Greg KH wrote: > On Sat, Nov 09, 2019 at 09:44:41PM +0300, Alexey Dobriyan wrote: > > > statsfs is a proposal for a new Linux kernel synthetic filesystem, > > > to be mounted in /sys/kernel/stats > > > > I think /proc experiment teaches pretty convincingly that dressing > > things into a filesystem can be done but ultimately is a stupid idea. > > It adds so much overhead for small-to-medium systems. > > > > > The first user of statsfs would be KVM, which is currently exposing > > > its stats in debugfs > > > > > Google has KVM patches to gather statistics in a binary format > > > > Which is a right thing to do. > > It's always "simpler" to just take binary data and suck it in. That > works for a year or so until another value needs to be supported. Or > removed. Or features are backported. > > The reason text values in individual files work is they are "self > describable" and "self discoverable". You "know" what the value is and > that it is supported because the file is there or not. With binary > values in a single file you do not know any of that. > > So you need some way of describing the data to userspace in order for > this to work properly over the next 20+ years. > > Maybe something like varlink which describes the data coming from the > kernel in an easy-to-handle format? Or something else, but just using > blobs does not work over the long-term, sorry. What about using a text format like YAML? Here's some benefits: - The fields are self describing based on the key name. - New fields can be easily added without breaking compatibility. - Allows for a script to easily parse the contents while keeping human readability. - Would work for systems that run busybox as their userspace without having to install additional tools. - Allows for a nested data structure. The downside is that the output would be larger than a binary interface but it's more maintainable in my opinion. Brian