osx - OS X serial port open with DTR low -

i've written serial port access code windows , os x on latter i've yet find way open port dtr low. (i'm trying avoid reseting arduino.) here simplest version of c code demonstrates problem:

const char *pathname = "/dev/tty.usbmodem411"; …. int main() {      int fd;     int status;     printf(" starting serial port program \n");     fd = open(pathname, o_rdwr | o_noctty | o_ndelay);      if (fd != -1) printf(" port opened, fd = %d\n",fd) ;     else     {         printf(" not open port\n");         return;     }     printf("closing port , quitting app\n");     if (fd !=-1) close(fd);     return 0; } 

i haven't found other open() flags help. can set dtr low after opening port via ioctl() doesn't since arduino resetting on open().

does know how keep dtr low during open() ? function of usb driver?