Linux Access Control Lists library (libacl, -lacl).  The function
returns  in  a  descriptor to the permission set in the ACL entry
indicated by Subsequent operations using the returned  permission
set  descriptor  operate on the permission set within the ACL en‐
try.  Any ACL entry descriptors that refer to the entry  referred
to  by  shall  continue to refer to those entries.  If any of the
following conditions occur, the function returns and sets to  the
corresponding  value:  The argument is not a valid descriptor for
an ACL entry.  IEEE Std 1003.1e draft 17 (“POSIX.1e”,  abandoned)
Derived  from the FreeBSD manual pages written by and adapted for
Linux by