[RFC PATCH v6 1/1] cmdline: Add capability to both append and prepend at the same time

[RFC PATCH v6 1/1] cmdline: Add capability to both append and prepend at the same time

[Christophe Leroy]

One user has expressed the need to both append and prepend some
built-in parameters to the command line provided by the bootloader.

Allthough it is a corner case, it is easy to implement so let's do it.

When the user chooses to prepend the bootloader provided command line
with the built-in command line, he is offered the possibility to enter
an additionnal built-in command line to be appended after the
bootloader provided command line.

It is a complementary feature which has no impact on the already
existing ones and/or the existing defconfig.

Suggested-by: Daniel Walker <danielwa@cisco.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
Sending this out as an RFC, applies on top of the series
("Implement GENERIC_CMDLINE"). I will add it to the series next spin
unless someone is against it.
---
 include/linux/cmdline.h |  3 +++
 init/Kconfig            | 12 +++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
index 020028e2bdf0..fb274a4d5519 100644
--- a/include/linux/cmdline.h
+++ b/include/linux/cmdline.h
@@ -36,6 +36,9 @@ static __always_inline bool __cmdline_build(char *dst, const char *src)
 
 	len = cmdline_strlcat(dst, src, COMMAND_LINE_SIZE);
 
+	if (IS_ENABLED(CONFIG_CMDLINE_PREPEND))
+		len = cmdline_strlcat(dst, " " CONFIG_CMDLINE_MORE, COMMAND_LINE_SIZE);
+
 	if (IS_ENABLED(CONFIG_CMDLINE_APPEND))
 		len = cmdline_strlcat(dst, " " CONFIG_CMDLINE, COMMAND_LINE_SIZE);
 
diff --git a/init/Kconfig b/init/Kconfig
index fa002e3765ab..cd3087ff4f28 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -128,6 +128,14 @@ config CMDLINE
 	  If this string is not empty, additional choices are proposed
 	  below to determine how it will be used by the kernel.
 
+config CMDLINE_MORE
+	string "Additional default kernel command string" if GENERIC_CMDLINE && CMDLINE_PREPEND
+	default ""
+	help
+	  Defines an additional default kernel command string.
+	  If this string is not empty, it is appended to the
+	  command-line arguments provided by the bootloader
+
 choice
 	prompt "Kernel command line type" if CMDLINE != ""
 	default CMDLINE_PREPEND if ARCH_WANT_CMDLINE_PREPEND_BY_DEFAULT
@@ -154,7 +162,9 @@ config CMDLINE_PREPEND
 	bool "Prepend to the bootloader kernel arguments"
 	help
 	  The default kernel command string will be prepended to the
-	  command-line arguments provided by the bootloader.
+	  command-line arguments provided by the bootloader. When this
+	  option is selected, another string can be added which will
+	  be appended.
 
 config CMDLINE_FORCE
 	bool "Always use the default kernel command string"
-- 
2.25.0

Re: [RFC PATCH v6 1/1] cmdline: Add capability to both append and prepend at the same time

[Rob Herring]

On Sun, Apr 4, 2021 at 12:20 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
> One user has expressed the need to both append and prepend some
> built-in parameters to the command line provided by the bootloader.
>
> Allthough it is a corner case, it is easy to implement so let's do it.
>
> When the user chooses to prepend the bootloader provided command line
> with the built-in command line, he is offered the possibility to enter
> an additionnal built-in command line to be appended after the
> bootloader provided command line.
>
> It is a complementary feature which has no impact on the already
> existing ones and/or the existing defconfig.
>
> Suggested-by: Daniel Walker <danielwa@cisco.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> Sending this out as an RFC, applies on top of the series
> ("Implement GENERIC_CMDLINE"). I will add it to the series next spin
> unless someone is against it.

Well, it works, but you are working around the existing kconfig and
the result is not great. You'd never design it this way.

Rob