Fixing Ceph ‘rbd: map failed: (6) No such device or address’

Tried to follow along here: http://docs.ceph.com/docs/hammer/start/quick-rbd/

But on my Ubuntu 16.04 client, when it got to the rbd map command, I got:

$ sudo rbd map foo --pool rbd --name client.admin
rbd: sysfs write failed
rbd: map failed: (6) No such device or address
$

Found the reason here: https://bugs.launchpad.net/ubuntu/+source/ceph/+bug/1578484

Got it working with:

$ rbd feature disable foo exclusive-lock object-map fast-diff deep-flatten

Now the map works:

$ sudo rbd map foo --pool rbd --name client.admin
/dev/rbd0
$

Has to do with these new Ceph features not being supported by the kernel client, which is why they must be disabled.