From patchwork Fri Jan 10 16:05:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Masami Hiramatsu (Google)" X-Patchwork-Id: 11327793 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 8A9AB109A for ; Fri, 10 Jan 2020 16:05:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 552CF20842 for ; Fri, 10 Jan 2020 16:05:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578672318; bh=J+uoasMQemisCi7nP/ysBiaXbQ81LYUTO5rAuHhMtGg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NDy1w6/BkppAEuk7D5mpBvaZd8lNRrOcVeeYaOq1+XKh+8RyCEY/fzryZjFfTINBR LKEjWQujujwURm5GvMuiwVc7/HydXOTkMj+4huxQkG65VNFDfP7Vq++dyd+Dvklhqj yqw7Da0Xx76kptPoaVXxJToTTlge74NxLzBUw7pg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728754AbgAJQFP (ORCPT ); Fri, 10 Jan 2020 11:05:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:53550 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728472AbgAJQFP (ORCPT ); Fri, 10 Jan 2020 11:05:15 -0500 Received: from localhost.localdomain (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 18A6C2082E; Fri, 10 Jan 2020 16:05:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578672313; bh=J+uoasMQemisCi7nP/ysBiaXbQ81LYUTO5rAuHhMtGg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xtPOHaZoa3p/gRvkDFpkokGcbRfRFmHEHXD13X6r7rPpWDQKcCyEC5V/MNrkzBBwr by3qNR3s64FJmNx0M8a0dbRRxkkbvXtfCupdA9ecYVozESVVAlbgT6m3ewwUyVUUO2 XfMS60VO117Qo79XWyyEiRKxpCTYby5yZA8WcH8E= From: Masami Hiramatsu To: Steven Rostedt Cc: Ingo Molnar , Frank Rowand , Randy Dunlap , Namhyung Kim , Tim Bird , Jiri Olsa , Arnaldo Carvalho de Melo , Tom Zanussi , Rob Herring , Andrew Morton , Thomas Gleixner , Greg Kroah-Hartman , Alexey Dobriyan , Jonathan Corbet , Linus Torvalds , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 09/22] Documentation: bootconfig: Add a doc for extended boot config Date: Sat, 11 Jan 2020 01:05:06 +0900 Message-Id: <157867230658.17873.9309879174829924324.stgit@devnote2> X-Mailer: git-send-email 2.20.1 In-Reply-To: <157867220019.17873.13377985653744804396.stgit@devnote2> References: <157867220019.17873.13377985653744804396.stgit@devnote2> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Add a documentation for extended boot config under admin-guide, since it is including the syntax of boot config. Signed-off-by: Masami Hiramatsu --- Changes in v6: - Add a note about comment after value. Changes in v5: - Fix to insert bootconfig to TOC list alphabetically. - Add notes about avaliable characters in values. - Fix to use correct quotes (``) for .rst. Changes in v4: - Rename suppremental kernel command line to boot config. - Update document according to the recent changes. - Add How to load it on boot. - Style bugfix. --- Documentation/admin-guide/bootconfig.rst | 184 ++++++++++++++++++++++++++++++ Documentation/admin-guide/index.rst | 1 MAINTAINERS | 1 3 files changed, 186 insertions(+) create mode 100644 Documentation/admin-guide/bootconfig.rst diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst new file mode 100644 index 000000000000..f7475df2a718 --- /dev/null +++ b/Documentation/admin-guide/bootconfig.rst @@ -0,0 +1,184 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================== +Boot Configuration +================== + +:Author: Masami Hiramatsu + +Overview +======== + +The boot configuration is expanding current kernel cmdline to support +additional key-value data when boot the kernel in an efficient way. +This allows adoministrators to pass a structured-Key config file. + +Config File Syntax +================== + +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``). +For array value, array entries are separated by comma (``,``). :: + +KEY[.WORD[...]] = VALUE[, VALUE2[...]][;] + +Each key word must contain only alphabets, numbers, dash (``-``) or underscore +(``_``). And each value only contains printable characters or spaces except +for delimiters such as semi-colon (``;``), new-line (``\n``), comma (``,``), +hash (``#``) and closing brace (``}``). + +If you want to use those delimiters in a value, you can use either double- +quotes (``"VALUE"``) or single-quotes (``'VALUE'``) to quote it. Note that +you can not escape these quotes. + +There can be a key which doesn't have value or has an empty value. Those keys +are used for checking the key exists or not (like a boolean). + +Key-Value Syntax +---------------- + +The boot config file syntax allows user to merge partially same word keys +by brace. For example:: + + foo.bar.baz = value1 + foo.bar.qux.quux = value2 + +These can be written also in:: + + foo.bar { + baz = value1 + qux.quux = value2 + } + +Or more shorter, written as following:: + + foo.bar { baz = value1; qux.quux = value2 } + +In both styles, same key words are automatically merged when parsing it +at boot time. So you can append similar trees or key-values. + +Comments +-------- + +The config syntax accepts shell-script style comments. The comments start +with hash ("#") until newline ("\n") will be ignored. + +:: + + # comment line + foo = value # value is set to foo. + bar = 1, # 1st element + 2, # 2nd element + 3 # 3rd element + +This is parsed as below:: + + foo = value + bar = 1, 2, 3 + +Note that you can not put a comment between value and delimiter(``,`` or +``;``). This means following config has a syntax error :: + + key = 1 # comment + ,2 + + +/proc/bootconfig +================ + +/proc/bootconfig is a user-space interface of the boot config. +Unlike /proc/cmdline, this file shows the key-value style list. +Each key-value pair is shown in each line with following style:: + + KEY[.WORDS...] = "[VALUE]"[,"VALUE2"...] + + +Boot Kernel With a Boot Config +============================== + +Since the boot configuration file is loaded with initrd, it will be added +to the end of the initrd (initramfs) image file. 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 config file +to/from initrd image. You can build it by follwoing command:: + + # make -C tools/bootconfig + +To add your boot config 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 + +To remove the config from the image, you can use -d option as below:: + + # tools/bootconfig/bootconfig -d /boot/initrd.img-X.Y.Z + + +C onfig File Limitation +====================== + +Currently the maximum config size size is 32KB and the total key-words (not +key-value entries) must be under 1024 nodes. +Note: this is not the number of entries but nodes, an entry must consume +more than 2 nodes (a key-word and a value). So theoretically, it will be +up to 512 key-value pairs. If keys contains 3 words in average, it can +contain 256 key-value pairs. In most cases, the number of config items +will be under 100 entries and smaller than 8KB, so it would be enough. +If the node number exceeds 1024, parser returns an error even if the file +size is smaller than 32KB. +Anyway, since bootconfig command verifies it when appending a boot config +to initrd image, user can notice it before boot. + + +Bootconfig APIs +=============== + +User can query or loop on key-value pairs, also it is possible to find +a root (prefix) key node and find key-values under that node. + +If you have a key string, you can query the value directly with the key +using xbc_find_value(). If you want to know what keys exist in the SKC +tree, you can use xbc_for_each_key_value() to iterate key-value pairs. +Note that you need to use xbc_array_for_each_value() for accessing +each arraies value, e.g.:: + + vnode = NULL; + xbc_find_value("key.word", &vnode); + if (vnode && xbc_node_is_array(vnode)) + xbc_array_for_each_value(vnode, value) { + printk("%s ", value); + } + +If you want to focus on keys which has a prefix string, you can use +xbc_find_node() to find a node which prefix key words, and iterate +keys under the prefix node with xbc_node_for_each_key_value(). + +But the most typical usage is to get the named value under prefix +or get the named array under prefix as below:: + + root = xbc_find_node("key.prefix"); + value = xbc_node_find_value(root, "option", &vnode); + ... + xbc_node_for_each_array_value(root, "array-option", value, anode) { + ... + } + +This accesses a value of "key.prefix.option" and an array of +"key.prefix.array-option". + +Locking is not needed, since after initialized, the config becomes readonly. +All data and keys must be copied if you need to modify it. + + +Functions and structures +======================== + +.. kernel-doc:: include/linux/bootconfig.h +.. kernel-doc:: lib/bootconfig.c + diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 4405b7485312..9e0f1e3fd152 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -64,6 +64,7 @@ configure specific aspects of kernel behavior to your liking. binderfs binfmt-misc blockdev/index + bootconfig braille-console btmrvl cgroup-v1/index diff --git a/MAINTAINERS b/MAINTAINERS index d0da06bdf3d8..c14a956343b9 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -15780,6 +15780,7 @@ F: lib/bootconfig.c F: fs/proc/bootconfig.c F: include/linux/bootconfig.h F: tools/bootconfig/* +F: Documentation/admin-guide/bootconfig.rst SUN3/3X M: Sam Creasey