linux-kernel - Re: O_CLOEXEC use for OPEN_TREE

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Message-ID: <20260114-alias-riefen-2cb8c09d0ded@brauner>
Date: Wed, 14 Jan 2026 17:03:17 +0100
From: Christian Brauner <brauner@...nel.org>
To: Florian Weimer <fweimer@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>, 
	David Howells <dhowells@...hat.com>, DJ Delorie <dj@...hat.com>
Subject: Re: O_CLOEXEC use for OPEN_TREE_CLOEXEC

On Tue, Jan 13, 2026 at 11:40:55PM +0100, Florian Weimer wrote:
> In <linux/mount.h>, we have this:
> 
> #define OPEN_TREE_CLOEXEC      O_CLOEXEC       /* Close the file on execve() */
> 
> This causes a few pain points for us to on the glibc side when we mirror
> this into <linux/mount.h> becuse O_CLOEXEC is defined in <fcntl.h>,
> which is one of the headers that's completely incompatible with the UAPI
> headers.
> 
> The reason why this is painful is because O_CLOEXEC has at least three
> different values across architectures: 0x80000, 0x200000, 0x400000
> 
> Even for the UAPI this isn't ideal because it effectively burns three
> open_tree flags, unless the flags are made architecture-specific, too.

I think that just got cargo-culted... A long time ago some API define as
O_CLOEXEC and now a lot of APIs have done the same. I'm pretty sure we
can't change that now but we can document that this shouldn't be ifdefed
and instead be a separate per-syscall bit. But I think that's the best
we can do right now.