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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Fri, 6 Aug 2021 10:18:19 +0200
Message-ID: <CAJfpegtOLgJO9VPpyHS0PB8JSeHjZ8aMwa0fMGrcRFsB8CTUJg@mail.gmail.com>
Subject: Re: [PATCH 07/11] exportfs: Allow filehandle lookup to cross internal
 mount points.
To:     Amir Goldstein <amir73il@gmail.com>
Cc:     NeilBrown <neilb@suse.de>, Christoph Hellwig <hch@infradead.org>,
        Josef Bacik <josef@toxicpanda.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
        David Sterba <dsterba@suse.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Linux Btrfs <linux-btrfs@vger.kernel.org>
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On Fri, 6 Aug 2021 at 10:08, Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Fri, Aug 6, 2021 at 10:52 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Thu, 29 Jul 2021 at 07:27, Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > > Given that today, subvolume mounts (or any mounts) on the lower layer
> > > are not followed by overlayfs, I don't really see the difference
> > > if mounts are created manually or automatically.
> > > Miklos?
> >
> > Never tried overlay on btrfs.  Subvolumes AFAIK do not use submounts
> > currently, they are a sort of hack where the st_dev changes when
> > crossing the subvolume boundary, but there's no sign of them in
> > /proc/mounts (there's no d_automount in btrfs).
>
> That's what Niel's patch 11/11 is proposing to add and that's the reason
> he was asking if this is going to break overlayfs over btrfs.
>
> My question was, regardless of btrfs, can ovl_lookup() treat automount
> dentries gracefully as empty dirs or just read them as is, instead of
> returning EREMOTE on lookup?
>
> The rationale is that we use a private mount and we are not following
> across mounts from layers anyway, so what do we care about
> auto or manual mounts?

I guess that depends on the use cases.  If no one cares (as is the
case apparently), the simplest is to leave it the way it is.

Thanks,
Miklos