From mboxrd@z Thu Jan 1 00:00:00 1970 From: Heiko Carstens Date: Tue, 14 Feb 2023 08:38:47 +0000 Subject: Re: [PATCH v3 00/24] Remove COMMAND_LINE_SIZE from uapi Message-Id: List-Id: References: <20230214074925.228106-1-alexghiti@rivosinc.com> In-Reply-To: <20230214074925.228106-1-alexghiti@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Alexandre Ghiti Cc: Jonathan Corbet , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Geert Uytterhoeven , Michal Simek , Thomas Bogendoerfer , "James E . J . Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Paul Walmsley , Palmer Dabbelt , Albert Ou , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , "David S . Miller" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Chris Zankel , Max Filippov , Arnd Bergmann , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org 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.