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

From: Alexandre Ghiti
Date: Mon Feb 13 2023 - 02:40:13 EST



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