From patchwork Mon Aug 26 03:16:25 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Masami Hiramatsu (Google)" X-Patchwork-Id: 11113885 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 AAF6E1813 for ; Mon, 26 Aug 2019 03:16:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7EC04217F4 for ; Mon, 26 Aug 2019 03:16:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566789397; bh=uWC/H1l7v6d+/MwTfG766K9JXtMKh6YTaqA+3BYw+7E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=2XPLVzVP+XOuGAAbvCwWpPiuyAXU/IcrzZIPyDLtk/HVi4Hf9Gvqlr4/E3uqzd5t9 1+S7EJHqVzxHsPmXK7C5Yn23wF84cadZebPNFXYLusCgqa0/gnMeSnkhesIadETA42 jqcKcaXvvP/zDi6cwuUNlY4fLLWUAk9h9c+64fYY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729485AbfHZDQd (ORCPT ); Sun, 25 Aug 2019 23:16:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:35766 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726434AbfHZDQd (ORCPT ); Sun, 25 Aug 2019 23:16:33 -0400 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 C2A1F2168B; Mon, 26 Aug 2019 03:16:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566789391; bh=uWC/H1l7v6d+/MwTfG766K9JXtMKh6YTaqA+3BYw+7E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LY8BlqA7MeEPLijQUsaoCM5739rOMHUHX8tuJTSV1xWTYqHVPwt4LXiU9F5SPf1z7 A/8GRdiGRwkfvOFaUkmuc3x7JRamQ6mk5CoblNiWYzcwusDUpaq9ZKAxP3PNG+gTHI IGDBnjQuz+aYkrql7nqEiNeNYkug3LQwmxVgKuRA= From: Masami Hiramatsu To: Steven Rostedt , Frank Rowand Cc: Ingo Molnar , 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: [RFC PATCH v3 04/19] Documentation: skc: Add a doc for supplemental kernel cmdline Date: Mon, 26 Aug 2019 12:16:25 +0900 Message-Id: <156678938543.21459.628373407524491520.stgit@devnote2> X-Mailer: git-send-email 2.20.1 In-Reply-To: <156678933823.21459.4100380582025186209.stgit@devnote2> References: <156678933823.21459.4100380582025186209.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 supplemental kernel cmdline under admin-guide, since it is including the syntax of SKC file. Signed-off-by: Masami Hiramatsu --- Documentation/admin-guide/index.rst | 1 Documentation/admin-guide/kernel-parameters.txt | 1 Documentation/admin-guide/skc.rst | 123 +++++++++++++++++++++++ MAINTAINERS | 1 4 files changed, 126 insertions(+) create mode 100644 Documentation/admin-guide/skc.rst diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 33feab2f4084..44b4cb61003a 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -106,6 +106,7 @@ configure specific aspects of kernel behavior to your liking. rtc svga video-output + skc .. only:: subproject and html diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9a955b1bd1bf..334ce59de23a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4277,6 +4277,7 @@ Pass the physical memory address and size of loaded supplemental kernel cmdline (SKC) text. This will be treated by bootloader which loads the SKC file. + See Documentation/admin-guide/skc.rst. slram= [HW,MTD] diff --git a/Documentation/admin-guide/skc.rst b/Documentation/admin-guide/skc.rst new file mode 100644 index 000000000000..dc6f7ba8e1d7 --- /dev/null +++ b/Documentation/admin-guide/skc.rst @@ -0,0 +1,123 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================ +Supplemental Kernel Commandline +================================ + +:Author: Masami Hiramatsu + +Overview +======== + +Supplemental Kernel Commandline (SKC) is expanding current kernel cmdline +to support additional key-value data when boot the kernel in efficient way. +This allows adoministrators to pass a tree-structured key-value text file +(SKC file) via bootloaders. + +SKC File Syntax +=============== + +SKC basic syntax is simple. Each key consists of dot-connected-words, and +key and value are connected by "=". The value has to be terminated by semi- +colon (";"). For array value, array entries are separated by comma (","). + +KEY[.WORD[...]] = VALUE[, VALUE2[...]]; + +Each key word only contains alphabet, number, dash ("-") or underscore ("_"). +If a value need to contain the delimiters, you can use double-quotes to +quote it. A double quote in VALUE can be escaped by backslash. 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). + +Tree Structure +-------------- + +SKC 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; +} + +In both style, same key words are automatically merged when parsing it +at boot time. So you can append similar trees or key-values. + +SKC File Limitation +=================== + +Currently the maximum SKC file size is 32KB and the total key-words (not +key-value entries) must be under 512 nodes. + +/proc/sup_cmdline +================= + +/proc/sup_cmdline is the user-space interface of supplemental kernel +cmdline. 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"...]; + +How to Pass at Boot +=================== + +SKC file is passed to kernel via memory, so the boot loader must support +loading SKC file. After loading the SKC file on memory, the boot loader +has to add "skc=PADDR,SIZE" argument to kernel cmdline, where the PADDR +is the physical address of the memory block and SIZE is the size of SKC +file. + +SKC 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 skc_find_value(). If you want to know what keys exist in the SKC +tree, you can use skc_for_each_key_value() to iterate key-value pairs. +Note that you need to use skc_array_for_each_value() for accessing +each arraies value, e.g. + +:: + + vnode = NULL; + skc_find_value("key.word", &vnode); + if (vnode && skc_node_is_array(vnode)) + skc_array_for_each_value(vnode, value) { + printk("%s ", value); + } + +If you want to focus on keys which has a prefix string, you can use +skc_find_node() to find a node which prefix key words, and iterate +keys under the prefix node with skc_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 = skc_find_node("key.prefix"); + value = skc_node_find_value(root, "option", &vnode); + ... + skc_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, SKC becomes readonly. +All data and keys must be copied if you need to modify it. + + +Functions and structures +======================== + +.. kernel-doc:: include/linux/skc.h +.. kernel-doc:: lib/skc.c + diff --git a/MAINTAINERS b/MAINTAINERS index 10dd38311d96..9c0b97643515 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -15368,6 +15368,7 @@ S: Maintained F: lib/skc.c F: fs/proc/sup_cmdline.c F: include/linux/skc.h +F: Documentation/admin-guide/skc.rst SUN3/3X M: Sam Creasey