Changing direction, how does csi do the mounting of cephfs? Found the section where this seems to happen but I know nothing about GO:

https://github.com/ceph/ceph-csi/tree/devel/internal/cephfs/mounter
https://github.com/ceph/ceph-csi/blob/devel/internal/cephfs/mounter/volumemounter.go

Seems to me we either need to use one of the options:

// Load available ceph mounters installed on system into availableMounters
// Called from driver.go's Run().
func LoadAvailableMounters(conf *util.Config) error {
	// #nosec
	fuseMounterProbe := exec.Command("ceph-fuse", "--version")
	// #nosec
	kernelMounterProbe := exec.Command("mount.ceph")

However, neither of these work based on the above outputs. Am I missing something stupidly easy?

Well, I had the mon IP wrong and it seems you need to specify the user. Finally got the thing to mount:

# oc scale deployment -n openshift-storage rook-ceph-mgr-a --replicas=0
# oc debug node/<WORKER_NODE>
# chroot /host
# mkdir /mnt/cephfs
# mount -t ceph <MON_1_IP>:6789:/ /mnt/cephfs -o name=admin,secret=<CLIENT.ADMIN.SECRET>

You can get the MON_IP by running 
# ceph mon stat

You can get the CLIENT.ADMIN.SECRET by running:
# ceph auth get client.admin

sh-4.4# mount -t ceph 172.30.185.225:6789:/ /mnt/cephfs -o name=admin,secret=<redacted>
sh-4.4#

sh-4.4# mount |grep ceph
...
172.30.185.225:6789:/ on /var/mnt/cephfs type ceph (rw,relatime,seclabel,name=admin,secret=<hidden>,acl)

I had the mon ip wrong and didn't specify the name=admin :)

Kotresh, PTAL.