Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Sun, 8 Jan 2023 15:04:25 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     paulmck@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
Message-Id: <20230108150425.426f2861e9db1152fa84508f@kernel.org>
In-Reply-To: <20230107162202.GA4028633@paulmck-ThinkPad-P17-Gen-1>
References: <20230105005838.GA1772817@paulmck-ThinkPad-P17-Gen-1>
        <20230108002215.c18df95b19acdd3207b379fa@kernel.org>
        <20230107162202.GA4028633@paulmck-ThinkPad-P17-Gen-1>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Sat, 7 Jan 2023 08:22:02 -0800
"Paul E. McKenney" <paulmck@kernel.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@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.

Yes, that differences confuse us...

> 
> > 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?

Yes! Thanks.

> 
> 							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>

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

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@kernel.org>