Re: [RFC PATCH] fs: allow opening overlayfs/erofs layers through O_ALT

On Wed, Jul 22, 2026 at 9:06=E2=80=AFAM Christian Brauner <[email protected]=
rg> wrote:

> Like I said before: I'm fine with an API where we can use open_tree() to
> see through into underlying layers, and given the right permission pull
> a mount out of it. That is a narrow, checkable primitive and it needs
> none of this. No new open flag, no second ->show_options, no metafs, no
> mnt_devname surgery. That part we can potentially do.

What, exactly, do you mean as the distinction between "[seeing]
through into underlying layers" and "[pulling] a mount out of it".  I
have a guess, but I'm not convinced that my guess is right.


Other than that question, I think I generally agree with you.  The
interesting operations here (getting an fd to something that was
previously inaccessible) are different enough from normal path lookups
that I think they deserve to be explicit syscalls or syscall modes,
not magic links.

--Andy