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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 E16F4C3F2D6 for ; Sat, 29 Feb 2020 05:59:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1D132087F for ; Sat, 29 Feb 2020 05:59:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ekh6UTfW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726752AbgB2F7t (ORCPT ); Sat, 29 Feb 2020 00:59:49 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:36142 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725747AbgB2F7t (ORCPT ); Sat, 29 Feb 2020 00:59:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description; bh=ohlSJGQzr6OomkRSMJ0q0CC7j3gpUcVQAsjMXoqgXwQ=; b=Ekh6UTfWNnb6YYQ06cQVM+HiXS G9yRyeiIHZpWLxLqgwxhd1jSvJaGh3PR5Hvp9wRGbyW92wqNyQ1oa1XCBnrY+kbmV2omumyBDcmry VjfVqwHtWqcpErDyZdG8TcJudBcDu/GeWByU14bzNWvm+sgqiTs+uhv9yyg0hnzA3oAmRmAB47LCi t198Y7kT8KjUmET8Z4ra4C3L4Vr5lAY4kZMnmPl5SD6W7nm53+Ex8KHCN8SSH8FCoBpovS8HDIq4N 2YFxRx/tbTTAzOVPIFvRGQiiC6Jqpa+l2AR9DOoFf9Fj2/K/XCztOC1LqoViZcwZCpWuuuVnlV+iI NBizwiYQ==; Received: from [2601:1c0:6280:3f0::19c2] by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j7vAB-0002cD-Pi; Sat, 29 Feb 2020 05:59:47 +0000 Subject: Re: [PATCH v2] Documentation: bootconfig: Update boot configuration documentation To: Masami Hiramatsu , Jonathan Corbet Cc: Steven Rostedt , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Markus Elfring References: <158287861133.18632.12035327305997207220.stgit@devnote2> <158287862131.18632.11822701514141299400.stgit@devnote2> From: Randy Dunlap Message-ID: <972ba3a8-9dd7-e043-d2f0-8fa8620686f7@infradead.org> Date: Fri, 28 Feb 2020 21:59:45 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <158287862131.18632.11822701514141299400.stgit@devnote2> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/28/20 12:30 AM, Masami Hiramatsu wrote: > Update boot configuration documentation. > > - Not using "config" abbreviation but configuration or description. > - Rewrite descriptions of node and its maxinum number. > - Add a section of use cases of boot configuration. > - Move how to use bootconfig to earlier section. > - Fix some typos, indents and format mistakes. > > Signed-off-by: Masami Hiramatsu > --- > Changes in v2: > - Fixes additional typos (Thanks Markus and Randy!) > - Change a section title to "Tree Structured Key". > --- > Documentation/admin-guide/bootconfig.rst | 180 +++++++++++++++++++----------- > Documentation/trace/boottime-trace.rst | 2 > 2 files changed, 116 insertions(+), 66 deletions(-) > > diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst > index cf2edcd09183..6a58d5e64896 100644 > --- a/Documentation/admin-guide/bootconfig.rst > +++ b/Documentation/admin-guide/bootconfig.rst > @@ -11,19 +11,98 @@ Boot Configuration > Overview > ======== > > -The boot configuration expands the current kernel command line to support > -additional key-value data when booting the kernel in an efficient way. > -This allows administrators to pass a structured-Key config file. > +Boot configuration expands the current kernel command line to support > +additional key-value data while booting the kernel in an efficient way. > +This allows administrators to pass a structured key configuration file > +as a way to supplement the kernel command line to pass system boot parameters. > > -Config File Syntax > -================== > +Compared with the kernel command line, the boot configuration can provide > +scalability (up to 32 KiB configuration data), readability (structured > +configuration with comments) and compact expression of option groups. Do the comments count in the 32 KiB of data? I.e., is the max bootconfig file size 32 KiB? > + > +When to Use the Boot Configuration? > +----------------------------------- > + > +The boot configuration supports kernel command line options and init daemon > +boot options. All sub-keys under "kernel" root key are passed as a part of > +kernel command line [1]_, and ones under "init" root key are passed as a part > +of init command line. For example, :: > + > + root=UUID=8cd79b08-bda0-4b9d-954c-5d5f34b98c82 ro quiet splash console=ttyS0,115200n8 console=tty0 > + > +This can be written as following boot configuration file.:: > + > + kernel { > + root = "UUID=8cd79b08-bda0-4b9d-954c-5d5f34b98c82" # nvme0n1p3 > + ro # mount rootfs as read only > + quiet # No console log > + splash # show splash image on boot screen > + console = "ttyS0,115200n8" # 1st console to serial device > + console += tty0 # add 2nd console > + } > + > +If you think that kernel/init options becomes too long to write in boot-loader > +configuration file or you want to comment on each option, the boot > +configuration may be suitable. If unsure, you can still continue to use the > +legacy kernel command line. > + > +Also, some subsystem may depend on the boot configuration, and it has own > +root key. For example, ftrace boot-time tracer uses "ftrace" root key to > +describe its options [2]_. In this case, you need to use the boot > +configuration. Does this say that "ftrace" requires use of bootconfig? It seems to say that. > + > +.. [1] See :ref:`Documentation/admin-guide/kernel-parameters.rst ` > +.. [2] See :ref:`Documentation/trace/boottime-trace.rst ` > + > + > +How to Use the Boot Configuration? > +---------------------------------- > + > +To enable the boot configuration support on your kernel, it must be built with > +``CONFIG_BOOT_CONFIG=y`` and ``CONFIG_BLK_DEV_INITRD=y``. > + > +Next, you can write a boot configuration file and attach it to initrd image. > + > +The boot configuration file is attached to the end of the initrd (initramfs) > +image file with size, checksum and 12-byte magic word as below. > + > +[initrd][bootconfig][size(u32)][checksum(u32)][#BOOTCONFIG\n] > + > +The Linux kernel decodes the last part of the initrd image in memory to > +get the boot configuration data. > +Because of this "piggyback" method, there is no need to change or > +update the boot loader and the kernel image itself. > + > +To do this operation, Linux kernel provides "bootconfig" command under > +tools/bootconfig, which allows admin to apply or delete the configuration > +file to/from initrd image. You can build it by the following command:: > + > + # make -C tools/bootconfig Please make that honor O=builddir instead of building in the kernel source tree and ignoring O=builddir. > + > +To add your boot configuration file to initrd image, run bootconfig as below > +(Old data is removed automatically if exists):: > + > + # tools/bootconfig/bootconfig -a your-config /boot/initrd.img-X.Y.Z > > -The boot config syntax is a simple structured key-value. Each key consists > -of dot-connected-words, and key and value are connected by ``=``. The value > -has to be terminated by semi-colon (``;``) or newline (``\n``). > +To remove the configuration from the image, you can use -d option as below:: > + > + # tools/bootconfig/bootconfig -d /boot/initrd.img-X.Y.Z > + > +At last, add ``bootconfig`` on the normal kernel command line to tell the > +kernel to look for the bootconfig at the end of the initrd file. For example:: > + > + GRUB_CMDLINE_LINUX="bootconfig" thanks. -- ~Randy