linux-kernel - Re: [PATCH 4/5] uapi: always define F_GETLK64/F_SETLK64/F

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Date:   Wed, 12 Jan 2022 08:56:09 +0100
From:   Christoph Hellwig <hch@....de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@....de>, Guo Ren <guoren@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [PATCH 4/5] uapi: always define F_GETLK64/F_SETLK64/F_SETLKW64
 in fcntl.h

On Tue, Jan 11, 2022 at 04:33:30PM +0100, Arnd Bergmann wrote:
> This is a very subtle change to the exported UAPI header contents:
> On 64-bit architectures, the three unusable numbers are now always
> shown, rather than depending on a user-controlled symbol.

Well, the change is bigger and less subtle.  Before this change the
constants were never visible to userspace at all (except on mips),
because the #ifdef CONFIG_64BIT it never set for userspace builds.

> This is probably what we want here for compatibility reasons, but I think
> it should be explained in the changelog text, and I'd like Jeff or Bruce
> to comment on it as well: the alternative here would be to make the
> uapi definition depend on __BITS_PER_LONG==32, which is
> technically the right thing to do but more a of a change.

I can change this to #if __BITS_PER_LONG==32 || defined(__KERNEL__),
but it will still be change in what userspace sees.