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[for-next,13/21] docs: bootconfig: Add how to embed the bootconfig into kernel

Message ID 20220427193641.826142252@goodmis.org (mailing list archive)
State New
Headers show
Series None | expand

Commit Message

Steven Rostedt April 27, 2022, 7:36 p.m. UTC
From: Masami Hiramatsu <mhiramat@kernel.org>

Add a description how to embed the bootconfig file into kernel.

Link: https://lkml.kernel.org/r/164921228987.1090670.16843569536974147213.stgit@devnote2

Cc: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 Documentation/admin-guide/bootconfig.rst | 31 +++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)
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diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index a1860fc0ca88..d99994345d41 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.
@@ -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_BOOT_CONFIG_EMBED_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