mon: block osd pool mksnap for fs pools

Commit 23db15d disabled pool snaps for the rados mksnap path. But
ceph osd pool mksnap was an alternate way that pool snaps could be
created.
This commit disables pool snaps via this alternate path as well.

NOTE:
Pool-level snaps and fs-level snaps can't co-exist since snap IDs are
likely to clash between the two different mechanisms and can result in
unintentional data loss when either of the snaps are deleted.

Fixes: https://tracker.ceph.com/issues/59552
Signed-off-by: Milind Changire <[email protected]>

Author: mchangir

src/mon/OSDMonitor.cc

@@ -13033,6 +13033,12 @@ bool OSDMonitor::prepare_command_impl(MonOpRequestRef op,
     if (pp->snap_exists(snapname.c_str())) {
       ss << "pool " << poolstr << " snap " << snapname << " already exists";
     } else {
+      if (const auto& fsmap = mon.mdsmon()->get_fsmap(); fsmap.pool_in_use(pool)) {
+	dout(20) << "pool-level snapshots have been disabled for pools "
+		    "attached to an fs - poolid:" << pool << dendl;
+	err = -EOPNOTSUPP;
+	goto reply;
+      }
       pp->add_snap(snapname.c_str(), ceph_clock_now());
       pp->set_snap_epoch(pending_inc.epoch);
       ss << "created pool " << poolstr << " snap " << snapname;