Re: [PATCH] asm-generic: Remove asm/setup.h from the UABI.

[Palmer Dabbelt]

On Fri, 23 Apr 2021 02:09:46 PDT (-0700), Arnd Bergmann wrote:
> On Fri, Apr 23, 2021 at 4:57 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> > From: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> >
> > I honestly have no idea if this is sane.
> >
> > 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 UABI 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.
> >
> > I couldn't think of a better way to ask about this then just sending the
> > patch.
>
> I think removing asm/setup.h from the uapi headers makes sense,
> but then we should do it consistently for all architectures as far
> as possible.
>
> Most architectures either use the generic file or they provide their
> own one-line version, so if we move them back, I would do it
> for all.

Ya, makes sense.  I just wanted to see if anyone had a reason for things 
being this way before I chased everything around.

> The architectures that have additional contents in this file
> are alpha, arm, and ia64. We I would leave those unchanged
> in that case.