-- http://man7.org/linux/man-pages/man2/setxattr.2.html
-- http://man7.org/linux/man-pages/man2/listxattr.2.html
-- http://man7.org/linux/man-pages/man2/getxattr.2.html
-- http://man7.org/linux/man-pages/man3/errno.3.html
-- https://www.freedesktop.org/wiki/CommonExtendedAttributes/