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Subject: Re: any idea about auto export multiple btrfs snapshots?
To:     Wang Yugui <wangyugui@e16-tech.com>,
        Frank Filz <ffilzlnx@mindspring.com>
Cc:     'NeilBrown' <neilb@suse.de>, linux-nfs@vger.kernel.org,
        Frank Filz <ffilz@redhat.com>
References: <20210621225541.3CEB.409509F4@e16-tech.com>
 <001901d766c5$cf427af0$6dc770d0$@mindspring.com>
 <20210622064158.98CA.409509F4@e16-tech.com>
From:   Frank Filz <ffilz@redhat.com>
Message-ID: <f2581d9f-dfe4-3280-80de-31683c9e647d@redhat.com>
Date:   Tue, 22 Jun 2021 10:34:35 -0700
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On 6/21/21 3:41 PM, Wang Yugui wrote:
> Hi,
>
>> OK thanks for the information. I think they will just work in nfs-ganesha as
>> long as the snapshots or subvols are mounted within an nfs-ganesha export or
>> are exported explicitly. nfs-ganesha has the equivalent of knfsd's
>> nohide/crossmnt options and when nfs-ganesha detects crossing a filesystem
>> boundary will lookup the filesystem via getmntend and listing btrfs subvols
>> and then expose that filesystem (via the fsid attribute) to the clients
>> where at least the Linux nfs client will detect a filesystem boundary and
>> create a new mount entry for it.
>
> Not only exported explicitly, but also kept in the same hierarchy.
>
> If we export
> /mnt/test		#the btrfs
> /mnt/test/sub1	# the btrfs subvol 1
> /mnt/test/sub2	# the btrfs subvol 2
>
> we need to make sure we will not access '/mnt/test/sub1' through '/mnt/test'
> from nfs client.
>
> current safe export:
> #/mnt/test		#the btrfs, not exported
> /mnt/test/sub1	# the btrfs subvol 1
> /mnt/test/sub2	# the btrfs subvol 2
>

What's the problem with exporting /mnt/test AND then exporting sub1 and 
sub2 as crossmnt exports? As far as I can tell, that seems to work just 
fine with nfs-ganesha.

Frank