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

Paul E. McKenney
2023-01-07T16:22:06Z

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.