Date:   Tue, 14 Feb 2023 10:19:02 +0100
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Alexandre Ghiti <alexghiti@rivosinc.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Richard Henderson <richard.henderson@linaro.org>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Matt Turner <mattst88@gmail.com>,
        Vineet Gupta <vgupta@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Michal Simek <monstr@monstr.eu>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
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        linux-arch@vger.kernel.org
Subject: Re: [PATCH v3 00/24] Remove COMMAND_LINE_SIZE from uapi
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On Tue, Feb 14, 2023 at 09:58:17AM +0100, Geert Uytterhoeven wrote:
> Hi Heiko,
> 
> On Tue, Feb 14, 2023 at 9:39 AM Heiko Carstens <hca@linux.ibm.com> wrote:
> > On Tue, Feb 14, 2023 at 08:49:01AM +0100, Alexandre Ghiti wrote:
> > > This all came up in the context of increasing COMMAND_LINE_SIZE in the
> > > RISC-V port.  In theory that's a UABI break, as COMMAND_LINE_SIZE is the
> > > maximum length of /proc/cmdline and userspace could staticly rely on
> > > that to be correct.
> > >
> > > Usually I wouldn't mess around with changing this sort of thing, but
> > > PowerPC increased it with a5980d064fe2 ("powerpc: Bump COMMAND_LINE_SIZE
> > > to 2048").  There are also a handful of examples of COMMAND_LINE_SIZE
> > > increasing, but they're from before the UAPI split so I'm not quite sure
> > > what that means: e5a6a1c90948 ("powerpc: derive COMMAND_LINE_SIZE from
> > > asm-generic"), 684d2fd48e71 ("[S390] kernel: Append scpdata to kernel
> > > boot command line"), 22242681cff5 ("MIPS: Extend COMMAND_LINE_SIZE"),
> > > and 2b74b85693c7 ("sh: Derive COMMAND_LINE_SIZE from
> > > asm-generic/setup.h.").
> > >
> > > It seems to me like COMMAND_LINE_SIZE really just shouldn't have been
> > > part of the uapi to begin with, and userspace should be able to handle
> > > /proc/cmdline of whatever length it turns out to be.  I don't see any
> > > references to COMMAND_LINE_SIZE anywhere but Linux via a quick Google
> > > search, but that's not really enough to consider it unused on my end.
> > >
> > > The feedback on the v1 seemed to indicate that COMMAND_LINE_SIZE really
> > > shouldn't be part of uapi, so this now touches all the ports.  I've
> > > tried to split this all out and leave it bisectable, but I haven't
> > > tested it all that aggressively.
> >
> > Just to confirm this assumption a bit more: that's actually the same
> > conclusion that we ended up with when commit 3da0243f906a ("s390: make
> > command line configurable") went upstream.
> 
> Commit 622021cd6c560ce7 ("s390: make command line configurable"),
> I assume?

Yes, sorry for that. I got distracted while writing and used the wrong
branch to look this up.