Description of problem:

If a snapshot is created on a parent directory of a subvolume, it shows up in the snapshot listing:

$ ceph fs volume create b
$ ceph fs subvolume create b foo
$ sudo mkdir /home/pdonnell/mnt/tmp.NdWboGH0TH/volumes/_nogroup/.snap/bar
$ ceph fs subvolume snapshot ls b foo
[
    {
        "name": "_bar_1099511627777" 
    }
]

These should be filtered out of the listing and operations on those snapshots should fail. Eventually we might want to have snapshots on subvolume groups again to have feature parity with RBD consistency groups [1] but those snapshot names can be fetched by listing the subvolume group snaps.

[1] https://tracker.ceph.com/projects/ceph/wiki/Consistency_groups


For more details, look into upstream tracker attached.