Re: O_CLOEXEC use for OPEN_TREE_CLOEXEC

[Christian Brauner]

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.