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J . Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , 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 References: <20230306100508.1171812-1-alexghiti@rivosinc.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: <20230306100508.1171812-1-alexghiti@rivosinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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-Daudé