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

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Date:   Sun,  4 Apr 2021 17:20:48 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     will@...nel.org, danielwa@...co.com, robh@...nel.org,
        daniel@...pelevich.san-francisco.ca.us, arnd@...nel.org,
        akpm@...ux-foundation.org
Cc:     linux-arch@...r.kernel.org, devicetree@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org,
        microblaze <monstr@...str.eu>, linux-mips@...r.kernel.org,
        nios2 <ley.foon.tan@...el.com>, openrisc@...ts.librecores.org,
        linux-hexagon@...r.kernel.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, linux-xtensa@...ux-xtensa.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org
Subject: [RFC PATCH v6 1/1] cmdline: Add capability to both append and prepend at
 the same time

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@...co.com>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.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