RTEMS with QEMU read from serial inside VM

[Мороз Олег]

Hello everyone. I've got a problem with reading data from /dev/ttys1 
configured  as UDP socket.
I'm starting qemu like this:
qemu-system-i386 -serial udp:127.0.0.1:4555 at 127.0.0.1:4556 -serial 
udp:127.0.0.1:4557 at 127.0.0.1:4558 -kernel zvezda_shell.exe

then i've opend a file and trying to read from it

   tty_in_descriptor = open("/dev/ttyS1",O_RDONLY);
   printf("tty_in_descriptor is %d\n",tty_in_descriptor);
   if (tty_in_descriptor)
   {
       while(1)
       printf("read() %d\n",read(tty_in_descriptor,buffer,1));
   }

at the same time i'm using a python program to send data to 4555 UDP port

The executions stops at the first data read.

How can i resolve it?