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Date:   Tue, 22 Jun 2021 06:41:58 +0800
From:   Wang Yugui <wangyugui@e16-tech.com>
To:     "Frank Filz" <ffilzlnx@mindspring.com>
Subject: Re: any idea about auto export multiple btrfs snapshots?
Cc:     "'NeilBrown'" <neilb@suse.de>, <linux-nfs@vger.kernel.org>
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References: <20210621225541.3CEB.409509F4@e16-tech.com> <001901d766c5$cf427af0$6dc770d0$@mindspring.com>
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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


Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/06/22