Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: [PATCH] asm-generic: Remove asm/setup.h from the UABI.
Date:   Thu, 22 Apr 2021 19:55:45 -0700
Message-Id: <20210423025545.313965-1-palmer@dabbelt.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Cc:     linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@android.com, Palmer Dabbelt <palmerdabbelt@google.com>
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     Arnd Bergmann <arnd@arndb.de>
Precedence: bulk

From: Palmer Dabbelt <palmerdabbelt@google.com>

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.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
 include/{uapi => }/asm-generic/setup.h | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename include/{uapi => }/asm-generic/setup.h (100%)

diff --git a/include/uapi/asm-generic/setup.h b/include/asm-generic/setup.h
similarity index 100%
rename from include/uapi/asm-generic/setup.h
rename to include/asm-generic/setup.h
-- 
2.31.1.498.g6c1eba8ee3d-goog