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    SubjectRe: [PATCH v3 00/24] Remove COMMAND_LINE_SIZE from uapi
    On Thu, Mar 2, 2023 at 4:17 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
    >
    > On Tue, 14 Feb 2023 01:19:02 PST (-0800), hca@linux.ibm.com wrote:
    > > On Tue, Feb 14, 2023 at 09:58:17AM +0100, Geert Uytterhoeven wrote:
    > >> Hi Heiko,
    > >>
    > >> On Tue, Feb 14, 2023 at 9:39 AM Heiko Carstens <hca@linux.ibm.com> wrote:
    > >> > 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.
    >
    > Thanks, I guess I'd missed that one. At some point I think there was
    > some discussion of making this a Kconfig for everyone, which seems
    > reasonable to me -- our use case for this being extended is syzkaller,
    > but we're sort of just picking a value that's big enough for now and
    > running with it.
    >
    > Probably best to get it out of uapi first, though, as that way at least
    > it's clear that it's not uABI.
    >
    > >> Commit 622021cd6c560ce7 ("s390: make command line configurable"),
    > >> I assume?
    > >
    > > Yes, sorry for that. I got distracted while writing and used the wrong
    > > branch to look this up.
    >
    > Alex: Probably worth adding that to the list in the cover letter as it
    > looks like you were planning on a v4 anyway (which I guess you now have
    > to do, given that I just added the issue to RISC-V).

    Yep, I will :)

    Thanks,

    Alex

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