Re: [PATCH v2 00/24] Remove COMMAND_LINE_SIZE from uapi

[Alexandre Ghiti]

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@xxxxxxxxxxx/>:
> > > * 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@xxxxxxxxxxxx/


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