Ceph » CephFS

To reproduce:
Setup ceph cluster with mds but don't create fs yet (nor the necessary pools). Equivalent to the result of MON=1 MDS=2 OSD=1 CEPH_NUM_FS=0 ../src/vstart.sh -d -n

Then add three pools:
ceph osd pool create foo 8 8
ceph osd pool create fs_data 8 8
ceph osd pool create fs_metadata 8 8

Create a fs instance with the 2 latter pools (or any pools with id !=1):
ceph fs new fs fs_metadata fs_data

Add pool with id 1 to fs:
ceph fs add_data_pool fs 1

Now mount the fs and create a file:
sudo ceph-fuse fs
touch fs/file
touch: setting times of 'fs/file': No such file or directory

Other operations will fail too , e.g. setting xattr ceph.dir.layout.pool to pool 1. Creating directories works.

PR: https://github.com/ceph/ceph/pull/15982