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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 2 Mar 2023 10:47:31 +0100
Message-ID: <CAMuHMdVC99kFpS9vL+HEqbXdDRMKVSW_t21X1p37d0oQufxKLw@mail.gmail.com>
Subject: Re: [PATCH v4 00/24] Remove COMMAND_LINE_SIZE from uapi
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
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Hi Alex,

On Thu, Mar 2, 2023 at 10:35 AM Alexandre Ghiti <alexghiti@rivosinc.com> 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.
>
> Changes since v3 <https://lore.kernel.org/all/20230214074925.228106-1-alexghiti@rivosinc.com/>:
> * Added RB/AB
> * Added a mention to commit 622021cd6c56 ("s390: make command line
>   configurable") in the cover letter

Thanks for the update!

 Apparently you forgot to add your own SoB?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds