Re: [PATCH RFC bootconfig] Allow forcing unconditional bootconfig processing

From: "Paul E. McKenney" <paulmck@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	corbet@lwn.net, akpm@linux-foundation.org,
	ndesaulniers@google.com, vbabka@suse.cz, hannes@cmpxchg.org,
	joel@joelfernandes.org, quic_neeraju@quicinc.com,
	urezki@gmail.com
Subject: Re: [PATCH RFC bootconfig] Allow forcing unconditional bootconfig processing
Date: Sat, 7 Jan 2023 08:22:02 -0800	[thread overview]
Message-ID: <20230107162202.GA4028633@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20230108002215.c18df95b19acdd3207b379fa@kernel.org>

On Sun, Jan 08, 2023 at 12:22:15AM +0900, Masami Hiramatsu wrote:
> On Wed, 4 Jan 2023 16:58:38 -0800
> "Paul E. McKenney" <paulmck@kernel.org> wrote:
> 
> > The BOOT_CONFIG family of Kconfig options allows a bootconfig file
> > containing kernel boot parameters to be embedded into an initrd or into
> > the kernel itself.  This can be extremely useful when deploying kernels
> > in cases where some of the boot parameters depend on the kernel version
> > rather than on the server hardware, firmware, or workload.
> > 
> > Unfortunately, the "bootconfig" kernel parameter must be specified in
> > order to cause the kernel to look for the embedded bootconfig file,
> > and it clearly does not help to embed this "bootconfig" kernel parameter
> > into that file.
> > 
> > Therefore, provide a new BOOT_CONFIG_FORCE Kconfig option that causes the
> > kernel to act as if the "bootconfig" kernel parameter had been specified.
> > In other words, kernels built with CONFIG_BOOT_CONFIG_FORCE=y will look
> > for the embedded bootconfig file even when the "bootconfig" kernel
> > parameter is omitted.  This permits kernel-version-dependent kernel
> > boot parameters to be embedded into the kernel image without the need to
> > (for example) update large numbers of boot loaders.
> 
> I like this because this is a simple solution. We have another option
> to specify "bootconfig" in CONFIG_CMDLINE, but it can be overwritten by
> bootloader. Thus, it is better to have this option so that user can
> always enable bootconfig.

Glad you like it!

In addition, if the help text is accurate, another shortcoming of
CONFIG_CMDLINE is that its semantics vary from one architecture to
another.  Some have CONFIG_CMDLINE override the boot-loader supplied
parameters, and others differ in the order in which the parameters
are processed.

> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thank you!

> BTW, maybe CONFIG_BOOT_CONFIG_EMBED is better to select this.
> (or at least recommend to enable this)

Like this?

							Thanx, Paul

------------------------------------------------------------------------

commit d09a1505c51a70da38b34ac38062977299aef742
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Sat Jan 7 08:09:22 2023 -0800

    bootconfig: Default BOOT_CONFIG_FORCE to y if BOOT_CONFIG_EMBED
    
    When a kernel is built with CONFIG_BOOT_CONFIG_EMBED=y, the intention
    will normally be to unconditionally provide the specified kernel-boot
    arguments to the kernel, as opposed to requiring a separately provided
    bootconfig parameter.  Therefore, make the BOOT_CONFIG_FORCE Kconfig
    option default to y in kernels built with CONFIG_BOOT_CONFIG_EMBED=y.
    
    The old semantics may be obtained by manually overriding this default.
    
    Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/init/Kconfig b/init/Kconfig
index 0fb19fa0edba9..97a0f14d9020d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1379,6 +1379,7 @@ config BOOT_CONFIG
 config BOOT_CONFIG_FORCE
 	bool "Force unconditional bootconfig processing"
 	depends on BOOT_CONFIG
+	default y if BOOT_CONFIG_EMBED
 	help
 	  With this Kconfig option set, BOOT_CONFIG processing is carried
 	  out even when the "bootconfig" kernel-boot parameter is omitted.
