FASYNC
#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK|O_DIRECT|FEXEC)
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FPOSIXSHM|FRDAHEAD| \
FC_FL(FASYNC),
oflags |= FASYNC;
if ((oflags ^ nflags) & FASYNC && so->so_version != SOV_STREAM) {
int async = nflags & FASYNC;
return (FASYNC);
retval = (flag & (FMASK | FASYNC));