It appears that a recent glibc update now enforces the requirement for a mode
parameter for open calls with the O_CREAT flag set. nfs-utils support code
defines a function xflock used by exportfs and mountd that calls open with
O_CREAT but no mode parameter. This causes exportfs and mountd to dump core,
with the error message:
*** invalid open64 call: O_CREAT without mode ***:rpc.mountd terminated