Re: [PATCH v5 00/26] Remove COMMAND_LINE_SIZE from uapi - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@linaro.org>
To: Alexandre Ghiti <alexghiti@rivosinc.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	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>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Michal Simek <monstr@monstr.eu>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
	Helge Deller <deller@gmx.de>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.co>
Subject: Re: [PATCH v5 00/26] Remove COMMAND_LINE_SIZE from uapi
Date: Mon, 6 Mar 2023 14:19:15 +0100	[thread overview]
Message-ID: <e1fa23ff-951e-176b-1a84-cbaab34ed44d__22789.9248989829$1678108776$gmane$org@linaro.org> (raw)
In-Reply-To: <20230306100508.1171812-1-alexghiti@rivosinc.com>

On 6/3/23 11:04, 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.
> 
> This issue was already considered in s390 and they reached the same
> conclusion in commit 622021cd6c56 ("s390: make command line
> configurable").
> 
> 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.

Series:
Reviewed-by: Philippe Mathieu-DaudÃ© <philmd@linaro.org>