The acl_calc_mask function is a POSIX.1e call that calculates and set the permissions associated with the ACL_MASK ACL entry of the ACL referred to by acl_p.
The value of new permissions are the union of the permissions granted by the ACL_GROUP, ACL_GROUP_OBJ, ACL_USER tag types which match processes in the file group class contained in the ACL referred to by acl_p.
If the ACL referred to by acl_p already contains an ACL_MASK entry, its permissions shall be overwritten; if it does not contain an ACL_MASK entry, one shall be added.
.Rv -std acl_calc_mask
The acl_calc_mask function fails if: