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From:   "NeilBrown" <neilb@suse.de>
To:     "Wang Yugui" <wangyugui@e16-tech.com>
Cc:     linux-nfs@vger.kernel.org
Subject: Re: any idea about auto export multiple btrfs snapshots?
In-reply-to: <162425113589.17441.4163890972298681569@noble.neil.brown.name>
References: <20210617122852.BE6A.409509F4@e16-tech.com>,
 <162397637680.29912.2268876490205517592@noble.neil.brown.name>,
 <20210618152631.F3DE.409509F4@e16-tech.com>,
 <162425113589.17441.4163890972298681569@noble.neil.brown.name>
Date:   Mon, 21 Jun 2021 15:13:27 +1000
Message-id: <162425240757.17441.3695249639927377778@noble.neil.brown.name>
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> > It seems more fixes are needed.
> 
> I think the problem is that the submount doesn't appear in /proc/mounts.
> "nfsd_fh()" in nfs-utils needs to be able to map from the uuid for a
> filesystem to the mount point.  To do this it walks through /proc/mounts
> checking the uuid of each filesystem.  If a filesystem isn't listed
> there, it obviously fails.
> 
> I guess you could add code to nfs-utils to do whatever "btrfs subvol
> list" does to make up for the fact that btrfs doesn't register in
> /proc/mounts.

Another approach might be to just change svcxdr_encode_fattr3() and
nfsd4_encode_fattr() in the 'FSIDSOJURCE_UUID' case to check if
dentry->d_inode has a different btrfs volume id to
exp->ex_path.dentry->d_inode.
If it does, then mix the volume id into the fsid somehow.

With that, you wouldn't want the first change I suggested.

NeilBrown