C_SEEK
{ "oseek", f_seek, C_SEEK, C_SEEK },
{ "seek", f_seek, C_SEEK, C_SEEK },
if ((oflag & O_TRUNC) && (ddflags & C_SEEK)) {
(oflag | (ddflags & (C_SEEK | C_NOTRUNC) ? 0 : O_TRUNC))
if ((ddflags & (C_OF | C_SEEK | C_NOTRUNC)) == (C_OF | C_SEEK))