From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3AAE7C for ; Mon, 28 Mar 2022 14:30:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92418C004DD; Mon, 28 Mar 2022 14:30:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648477827; bh=0fJAVjmpmWefISZQ/CbYY4ljN8LhkUpwEfBUSoXFz/o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Q8zOPgsibK2EPWrixhHmPrrsyfIIk1vXGGUX4UZPseQI8k2V40kOCDhMYgf0VUJGR UYhNvemk7Iy8rpsOc/X+s+xFW1CgxLztCugnh5d8wPkMH5zoj/ZahjFE29nto9KXuH VeCiHgQ6IInNTVlrwgFCE0c6drf6NLhKNt6ie4DBpLMfRVc7oXZ7AwitTVJJWp2Wdq M5j5kzDgZFq4WzSp62Dh6ogLVerIPjqs6u1tMw6jQfwu2Mv/6QG6Ur+nD22lmO2YgU cDcwX2z29hmohmMdNlMgfN6l9Rftnp5UVjuBI1DNSWtT2Kr9I3ZJuvbjRvYB8YOq1o zUgMva6949LJw== 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 v5 3/3] docs: bootconfig: Add how to embed the bootconfig into kernel Date: Mon, 28 Mar 2022 23:30:22 +0900 Message-Id: <164847782202.3060675.17704713855690661713.stgit@devnote2> X-Mailer: git-send-email 2.25.1 In-Reply-To: <164847778869.3060675.8115416881394543419.stgit@devnote2> References: <164847778869.3060675.8115416881394543419.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Add a description how to embed the bootconfig file into kernel. Signed-off-by: Masami Hiramatsu --- Changes in v5: - Update CONFIG_EMBED_BOOT_CONFIG_FILE which can accept relative path. 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 | 31 +++++++++++++++++++++++++++--- 1 file changed, 28 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst index a1860fc0ca88..83a2a0cc9afa 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 +202,25 @@ 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 an absolute path or a relative +path to the bootconfig file from source tree or object tree. +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 =================================