Ceph » Linux kernel client

See this failure:
http://pulpito.ceph.com/jspray-2016-12-06_12:37:38-kcephfs:recovery-master-testing-basic-smithi/611135

The client is getting the FSMapUser as we can see in the mon log:

2016-12-06 14:30:01.582024 7f07e8a13700  1 -- 172.21.15.1:6789/0 --> 172.21.15.95:0/1525586736 -- fsmap.user(e 45) v1 -- 0x564acc13d000 con 0

...but it's giving an ENOENT when trying to look up the mds_namespace 'alpha'

2016-12-06T14:30:01.563 INFO:teuthology.orchestra.run.smithi095:Running: 'sudo adjust-ulimits ceph-coverage /home/ubuntu/cephtest/archive/coverage /sbin/mount.ceph 172.21.15.1:6789:/ /home/ubuntu/cephtest/mnt.0 -v -o name=0,secretfile=/home/ubuntu/cephtest/ceph.data/client.0.secret,mds_namespace=alpha'
2016-12-06T14:30:01.663 INFO:teuthology.orchestra.run.smithi095.stdout:parsing options: name=0,secretfile=/home/ubuntu/cephtest/ceph.data/client.0.secret,mds_namespace=alpha
2016-12-06T14:30:01.663 INFO:teuthology.orchestra.run.smithi095.stdout:ceph: Unknown mount option mds_namespace
2016-12-06T14:30:01.663 INFO:teuthology.orchestra.run.smithi095.stdout:mount error 2 = No such file or directory

(The 'unknown mount option' seems unrelated http://tracker.ceph.com/issues/18159 -- we can be certain that the option is making it to the kernel because it only subscribes to fsmap.user when mds_namespace is set)