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From:   "NeilBrown" <neilb@suse.de>
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     "Christoph Hellwig" <hch@infradead.org>,
        "Josef Bacik" <josef@toxicpanda.com>,
        "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@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 09/11] nfsd: Allow filehandle lookup to cross internal
 mount points.
In-reply-to: <20210728191539.GB3152@fieldses.org>
References: <162742539595.32498.13687924366155737575.stgit@noble.brown>,
 <162742546556.32498.16708762469227881912.stgit@noble.brown>,
 <20210728191539.GB3152@fieldses.org>
Date:   Thu, 29 Jul 2021 08:29:31 +1000
Message-id: <162751137120.21659.13367329474467230018@noble.neil.brown.name>
Precedence: bulk

On Thu, 29 Jul 2021, J. Bruce Fields wrote:
> On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:
> > Enhance nfsd to detect internal mounts and to cross them without
> > requiring a new export.
> 
> Why don't we want a new export?
> 
> (Honest question, it's not obvious to me what the best behavior is.)

Because a new export means asking user-space to determine if the mount
is exported and to provide a filehandle-prefix for it.  A large part of
the point of this it to avoid using a different filehandle-prefix.

I haven't yet thought deeply about how the 'crossmnt' flag (for v3)
should affect crossing these internal mounts.  My current feeling is
that it shouldn't as it really is just one big filesystem being
exported, which happens to internally have different inode-number
spaces. 
Unfortuantely this technically violates the RFC as the fsid is not meant
to change when you do a LOOKUP ...

NeilBrown