linux-kernel - Re: [RFC PATCH v4 01/22] bootconfig: Add Extra Boot Config support

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Date:   Thu, 6 Feb 2020 18:41:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Frank Rowand <frowand.list@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Tim Bird <Tim.Bird@...y.com>, Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v4 01/22] bootconfig: Add Extra Boot Config support

Hi Geert,

On Thu, 6 Feb 2020 10:08:22 +0100
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> Hi Steven,
> 
> On Mon, Dec 9, 2019 at 4:55 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Mon, 9 Dec 2019 14:50:09 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > > On Sun, 8 Dec 2019 11:34:32 -0800
> > > Randy Dunlap <rdunlap@...radead.org> wrote:
> > > > On 12/2/19 2:13 AM, Masami Hiramatsu wrote:
> > > > > diff --git a/init/Kconfig b/init/Kconfig
> > > > > index 67a602ee17f1..13bb3eac804c 100644
> > > > > --- a/init/Kconfig
> > > > > +++ b/init/Kconfig
> > > > > @@ -1235,6 +1235,17 @@ source "usr/Kconfig"
> > > > >
> > > > >  endif
> > > > >
> > > > > +config BOOT_CONFIG
> > > > > + bool "Boot config support"
> > > > > + select LIBXBC
> > > > > + default y
> > > >
> > > > questionable "default y".
> > > > That needs lots of justification.
> > >
> > > OK, I can make it 'n' by default.
> > >
> > > I thought that was OK because most of the memories for the
> > > bootconfig support were released after initialization.
> > > If user doesn't pass the bootconfig, only the code for
> > > /proc/bootconfig remains on runtime memory.
> >
> > As 'n' is usually the default, I will argue this should be 'y'!
> >
> > This is not some new fancy feature, or device that Linus
> > complains about "my X is important!". I will say this X *is* important!
> > This will (I hope) become standard in all kernel configs. One could even
> > argue that there shouldn't even be a config for this at all (forced
> > 'y'). This would hurt more not to have than to have. I would hate to
> > try to load special options only to find out that the kernel was
> > compiled with default configs and this wasn't enabled.
> 
> Let's bite ;-)
> 
> If one could even argue that there shouldn't even be a config for this
> at all, then why are there two? There's a visible BOOT_CONFIG config,
> and an invisible LIBXBC config.

Oh, I just imitated LIBFDT. 

> Are there other users planned for LIBXBC?

No, no more. I had a plan to use it for ftrace scripting interface,
but I found it should be easy to make a userspace tool using
lib/bootconfig.c directly :)

So it is OK to replace it with BOOT_CONFIG now.

Thank you!

-- 
Masami Hiramatsu <mhiramat@...nel.org>