PendingReleaseNotes: add note about fallocate mode 0

fallocate now returns EOPNOTSUPP for mode 0

Signed-off-by: Milind Changire <[email protected]>

Author: mchangir

PendingReleaseNotes

@@ -43,6 +43,10 @@
   there are alternative monitoring solutions, like `prometheus`, which is the most
   widely adopted among the Ceph user community.
 
+* CephFS: EOPNOTSUPP (Operation not supported ) is now returned by the CephFS
+  fuse client for `fallocate` for the default case (i.e. mode == 0) since
+  CephFS does not support disk space reservation. The only flags supported are
+  `FALLOC_FL_KEEP_SIZE` and `FALLOC_FL_PUNCH_HOLE`.
 
 >=19.0.0