linux-kernel - Re: [PATCH v2 00/24] Remove COMMAND_LINE

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Message-Id: <aa40847d-1814-4a20-821e-650c8f1f7cad@app.fastmail.com>
Date:   Fri, 10 Feb 2023 20:37:37 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Alexandre Ghiti" <alex@...ti.fr>,
        "Palmer Dabbelt" <palmer@...osinc.com>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/24] Remove COMMAND_LINE_SIZE from uapi

On Fri, Feb 10, 2023, at 18:10, Alexandre Ghiti wrote:
> On 12/11/22 07:13, Palmer Dabbelt 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.
>>
>> Changes since v1 <https://lore.kernel.org/all/20210423025545.313965-1-palmer@dabbelt.com/>:
>> * Touches every arch.
>>
>>
>
> The command line size is still an issue on riscv, any comment on this so 
> we can make progress?

I think this makes sense overall, but I see there were a couple
of architecture specific regressions introduced in v2 that should
be resolved, see

https://lore.kernel.org/all/20221211061358.28035-1-palmer@rivosinc.com/

for the archive of this thread.

     Arnd