The full name of PWL is persistent write log, and the full name of
RWL is replica write log. Change the title to make it consistent
with the name of the feature and better reflect its design.
Signed-off-by: Yin Congmin <congmin.yin@intel.com>
A discussion on the ceph-users list uncovered a bit of uncertainty
about how exclusive locking works:
https://www.mail-archive.com/ceph-users@lists.ceph.com/msg56910.html
Add a bit of background information about exclusive locks, and
cross-reference the documentatation on OpenStack, and on CephX.
Signed-off-by: Florian Haas <florian@citynetwork.eu>
