Linux Access Control Lists library (libacl, -lacl).  The function
returns  the  number of ACL entries that are contained in the ACL
referred to by the argument The function returns  the  number  of
entries in if successful; otherwise the value is returned and the
global variable is set to indicate the error.  If any of the fol‐
lowing  conditions  occur,  the  function returns and sets to the
corresponding value: The argument is not a valid  pointer  to  an
ACL.  This is a non‐portable, Linux specific extension to the ACL
manipulation  functions  defined  in  IEEE  Std  1003.1e draft 17
(“POSIX.1e”, abandoned).  Written by