From patchwork Sat Mar 26 23:53:39 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Masami Hiramatsu (Google)" X-Patchwork-Id: 12792698 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 914FFC433F5 for ; Sat, 26 Mar 2022 23:54:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230273AbiCZXzs (ORCPT ); Sat, 26 Mar 2022 19:55:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231463AbiCZXzX (ORCPT ); Sat, 26 Mar 2022 19:55:23 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A142644754; Sat, 26 Mar 2022 16:53:46 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 436C4B80BEB; Sat, 26 Mar 2022 23:53:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9C1EC340E8; Sat, 26 Mar 2022 23:53:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648338823; bh=FwRy95YaoTK2BNBsAgnwyFkUwJ1K6hC1h5SRyvWqEcc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TC7GMV4KOydd0o9Sv2pMrXCgkLtTtemg+MW7uzGGxJ1gFaosw14E060Fop5Oyv5hk A2i3gXa9ljAOqQsYlGKnDmSG6x1fouZxwUJL35FKIIsNBvFrCLvRa3WhL8bLA5Kd2H 0FjREGKR0cPpShhWmUyX5oT1w3Ta5Hq3YYKtDBiFnSi+APxqee2h3/+gjePI13c444 DCdnDh7TGLEyx4+QmzUCrADo5XHVQoH1ZI9+e+Apf/wUqmgFbxvq67N1B4sqyUTYoY I8wJmmR6m7qZTM4Z9O0PaBRdxxuYQmNHGvJFKzKFVvleXpD6WAG1FwJyYrUCnaJMA8 QD4fZPJJgWvhg== From: Masami Hiramatsu To: Steven Rostedt Cc: Masami Hiramatsu , Padmanabha Srinivasaiah , LKML , Jonathan Corbet , linux-doc@vger.kernel.org, Randy Dunlap , Nick Desaulniers , Sami Tolvanen , Nathan Chancellor , llvm@lists.linux.dev, Masahiro Yamada , Linux Kbuild mailing list Subject: [PATCH v4 3/3] docs: bootconfig: Add how to embed the bootconfig into kernel Date: Sun, 27 Mar 2022 08:53:39 +0900 Message-Id: <164833881933.2575750.9855651229937143999.stgit@devnote2> X-Mailer: git-send-email 2.25.1 In-Reply-To: <164833878595.2575750.1483106296151574233.stgit@devnote2> References: <164833878595.2575750.1483106296151574233.stgit@devnote2> User-Agent: StGit/0.19 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Add a description how to embed the bootconfig file into kernel. Signed-off-by: Masami Hiramatsu --- Changes in v3: - Fix typos. Changes in v2: - Corrected the text accoding to Randy's suggestion. - Do not reccomend to use relative path for CONFIG_EMBED_BOOT_CONFIG_FILE. --- Documentation/admin-guide/bootconfig.rst | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst index a1860fc0ca88..9028e0f1307b 100644 --- a/Documentation/admin-guide/bootconfig.rst +++ b/Documentation/admin-guide/bootconfig.rst @@ -158,9 +158,15 @@ Each key-value pair is shown in each line with following style:: 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 with padding, size, -checksum and 12-byte magic word as below. +There are two options to boot the kernel with bootconfig: attaching the +bootconfig to the initrd image or embedding it in the kernel itself. + +Attaching a Boot Config to Initrd +--------------------------------- + +Since the boot configuration file is loaded with initrd by default, +it will be added to the end of the initrd (initramfs) image file with +padding, size, checksum and 12-byte magic word as below. [initrd][bootconfig][padding][size(le32)][checksum(le32)][#BOOTCONFIG\n] @@ -196,6 +202,24 @@ To remove the config from the image, you can use -d option as below:: Then add "bootconfig" on the normal kernel command line to tell the kernel to look for the bootconfig at the end of the initrd file. +Embedding a Boot Config into Kernel +----------------------------------- + +If you can not use initrd, you can also embed the bootconfig file in the +kernel by Kconfig options. In this case, you need to recompile the kernel +with the following configs:: + + CONFIG_EMBED_BOOT_CONFIG=y + CONFIG_EMBED_BOOT_CONFIG_FILE="/PATH/TO/BOOTCONFIG/FILE" + +``CONFIG_EMBED_BOOT_CONFIG_FILE`` requires a correct absolute path to +the bootconfig file. The kernel will embed it as the default bootconfig. + +Just as when attaching the bootconfig to the initrd, you need ``bootconfig`` +option on the kernel command line to enable the embedded bootconfig. + +Note that even if you set this option, you can override the embedded +bootconfig by another bootconfig which attached to the initrd. Kernel parameters via Boot Config =================================