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

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Message-ID: <20251021131633.26700Dd6-hca@linux.ibm.com>
Date: Tue, 21 Oct 2025 15:16:33 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Doug Anderson <dianders@...omium.org>,
        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

On Tue, Oct 21, 2025 at 09:05:48AM +0200, Geert Uytterhoeven wrote:
> 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.

That was just a follow-on patch of commit 5ecb2da660ab ("s390: support command
lines longer than 896 bytes") which solved the real problem with a too short
maximum command line size back then. In order to never have to deal with this
sort of problem again it was made configurable.

But I doubt that anybody will change the default ever.