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From:   "NeilBrown" <neilb@suse.de>
To:     "Al Viro" <viro@zeniv.linux.org.uk>
Cc:     "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>, linux-fsdevel@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 05/11] VFS: new function: mount_is_internal()
In-reply-to: <YQC99cfMkbGz3u1q@zeniv-ca.linux.org.uk>
References: <162742539595.32498.13687924366155737575.stgit@noble.brown>,
 <162742546552.32498.14429836898036234922.stgit@noble.brown>,
 <YQC99cfMkbGz3u1q@zeniv-ca.linux.org.uk>
Date:   Wed, 28 Jul 2021 13:32:45 +1000
Message-id: <162744316594.21659.15176398691432709276@noble.neil.brown.name>
Precedence: bulk

On Wed, 28 Jul 2021, Al Viro wrote:
> On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:
> > This patch introduces the concept of an "internal" mount which is a
> > mount where a filesystem has create the mount itself.
> > 
> > Both the mounted-on-dentry and the mount's root dentry must refer to the
> > same superblock (they may be the same dentry), and the mounted-on dentry
> > must be an automount.
> 
> And what happens if you mount --move it?
> 
> 
If you move the mount, then the mounted-on dentry would not longer be an
automount (....  I assume???...) so it would not longer be
mount_is_internal().

I think that is reasonable.  Whoever moved the mount has now taken over
responsibility for it - it no longer is controlled by the filesystem.
The moving will have removed the mount from the list of auto-expire
mounts, and the mount-trap will now be exposed and can be mounted-on
again.

It would be just like unmounting the automount, and bind-mounting the
same dentry elsewhere.

NeilBrown