linux-kernel - Re: [PATCH RFC bootconfig] Allow forcing unconditional bootconfig processing

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Date:   Sun, 8 Jan 2023 20:25:01 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        corbet@....net, akpm@...ux-foundation.org, ndesaulniers@...gle.com,
        vbabka@...e.cz, hannes@...xchg.org, joel@...lfernandes.org,
        quic_neeraju@...cinc.com, urezki@...il.com
Subject: Re: [PATCH RFC bootconfig] Allow forcing unconditional bootconfig
 processing

On Sun, Jan 08, 2023 at 03:04:25PM +0900, Masami Hiramatsu wrote:
> On Sat, 7 Jan 2023 08:22:02 -0800
> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > 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@...nel.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.
> 
> Yes, that differences confuse us...

I am glad that it is not just me.  ;-)

I will add words to that effect to the commit log.

> > > Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Thank you!
> > 
> > > BTW, maybe CONFIG_BOOT_CONFIG_EMBED is better to select this.
> > > (or at least recommend to enable this)
> > 
> > Like this?
> 
> Yes! Thanks.
> 
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit d09a1505c51a70da38b34ac38062977299aef742
> > Author: Paul E. McKenney <paulmck@...nel.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@...nel.org>
> >     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Applied, thank you!

							Thanx, Paul

> Thank you!
> 
> > 
> > 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.
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>