linux-kernel - Re: [PATCH] init/main.c: Wrap long kernel cmdline when printing to logs

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Message-ID: <CAMuHMdWGb0jVt9ziBtWdHWC9omPAFMHVPBHDpv0F1XzvR0THpg@mail.gmail.com>
Date: Tue, 21 Oct 2025 09:05:48 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Doug Anderson <dianders@...omium.org>
Cc: Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org, 
	Andrew Chant <achant@...gle.com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Brian Gerst <brgerst@...il.com>, 
	Christian Brauner <brauner@...nel.org>, Francesco Valla <francesco@...la.it>, 
	Guo Weikang <guoweikang.kernel@...il.com>, Huacai Chen <chenhuacai@...nel.org>, 
	Jan Hendrik Farr <kernel@...rr.cc>, Jeff Xu <jeffxu@...omium.org>, Kees Cook <kees@...nel.org>, 
	Masahiro Yamada <masahiroy@...nel.org>, Michal Koutný <mkoutny@...e.com>, 
	Miguel Ojeda <ojeda@...nel.org>, "Mike Rapoport (Microsoft)" <rppt@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Tejun Heo <tj@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	"Uladzislau Rezki (Sony)" <urezki@...il.com>, Sven Schnelle <svens@...ux.ibm.com>, 
	linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [PATCH] init/main.c: Wrap long kernel cmdline when printing to logs

Hi Doug,

CC s390

On Mon, 20 Oct 2025 at 18:04, Doug Anderson <dianders@...omium.org> wrote:
> On Mon, Oct 20, 2025 at 8:42 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Mon, 20 Oct 2025 at 17:33, Doug Anderson <dianders@...omium.org> wrote:
> > > Printing the command line to the kernel log buffer is one of the very
> > > rare cases where:
> > > * There's a legitimate reason to print a (potentially) very long
> > > string to the kernel buffer.
> >
> > arch/s390/Kconfig:
> >
> >     config COMMAND_LINE_SIZE
> >             int "Maximum size of kernel command line"
> >             default 4096
> >             range 896 1048576
> >
> > Yummy...
>
> Wow, what are they expecting to stuff in there? An encoded initramfs
> or something? I kinda feel like the 1MB number isn't something anyone
> expects but is a number picked to effectively be "unlimited".

Dunno, commit 622021cd6c560ce7 ("s390: make command line configurable")
lacks the "why" part.

> Do you have a suggestion of what my code should do if it sees such a
> long cmdline? At small numbers (4K, 8K, maybe even 32K) printing the
> wrapped cmdline is nice. Above that, maybe it should just print
> something like "<cmdline truncated>" or something?

I don't know, I never saw truncated kernel command lines myself.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds