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

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Date:   Mon, 13 Feb 2023 08:40:02 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Arnd Bergmann <arnd@...db.de>,
        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 2/10/23 20:37, Arnd Bergmann wrote:
> 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/


Thanks, I had not noticed those failures. I'll take over and send a v3 
that fixes that,

Thanks again,

Alex


>
> for the archive of this thread.
>
>       Arnd