linux-kernel - Re: O_CLOEXEC use for OPEN_TREE

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Message-ID: <CALCETrWMWs3_G5JhJb7+h+JQjpqXxqOh2vNcQaG1HuXjaeCqQw@mail.gmail.com>
Date: Wed, 14 Jan 2026 11:42:57 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Christian Brauner <brauner@...nel.org>
Cc: Florian Weimer <fweimer@...hat.com>, 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 Wed, Jan 14, 2026 at 8:09 AM Christian Brauner <brauner@...nel.org> wrote:
>
> 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.
>

How about, for future syscalls, we make CLOEXEC unconditional?  If
anyone wants an ofd to get inherited across exec, they can F_SETFD it
themselves.

--Andy