linux-kernel - Re: How to support directory opacity in a filesystem for overlayfs to use?

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Message-ID: <112184.1736870193@warthog.procyon.org.uk>
Date: Tue, 14 Jan 2025 15:56:33 +0000
From: David Howells <dhowells@...hat.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: dhowells@...hat.com, mszeredi@...hat.com,
    linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: How to support directory opacity in a filesystem for overlayfs to use?

Miklos Szeredi <miklos@...redi.hu> wrote:

> On Tue, 14 Jan 2025 at 16:15, David Howells <dhowells@...hat.com> wrote:
> 
> > What's the best way for a network filesystem to make a native
> > directory-is-opaque flag available to the system?  Is it best to catch
> > setxattr/getxattr/removexattr("overlay.opaque") and translate these into the
> > RPCs to wrangle the flag?
> 
> I don't know.  Out of curiosity, which filesystem is it?

One of the varieties of AFS.  Unfortunately, xattrs aren't a thing and can't
easily be added because of the volume transfer and backup protocols and
formats.

> There's "trusted.overlay.opaque" and "user.overlay.opaque" and are
> used in different scenarios.   There was also talk of making the
> "trusted." namespace nest inside user namespaces, but apparently it's
> not so important.
> 
> Which one would you like to emulate?

Um - I don't know the difference to answer that question.

David