I was writing a program communicating via COMM with read/write, and thinking of setting the comm to synchronous mode, 
such that write() function won't return until all data in the buffer has been sent. So, I tried to set the O_DSYNC flag 
by calling fcntl() function. But apparently it doesn't work, fcntl function call return with errorno:22 (/* Invalid 
argument*/). 

Anyone has any idea? I guess qnx does't support O_DSYNC flag for serial port, is that right? 

Any idea how to walk around this: how to write() comm in a synchronous mode?

Attached is the code I used.

Thanks.


//*************** Code ***************************

#include <iostream>
#include <fstream>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <pthread.h>
#include <fcntl.h>
#include <stdarg.h>
#include <termios.h>
#include <time.h>
#include <errno.h>

using namespace std;
		
int main (int argc, char **argv)
{
	int serf = open("/dev/ser1", O_RDWR );
	if (serf == -1)
	{
		cout << "Fail to open COM." << endl;
		exit(1);
	}

	int retval = fcntl(serf, F_SETFL, O_DSYNC );
    if( retval == -1 ) {
        printf( "error setting stdout flags, with errorno=%d\n", errno);
        return EXIT_FAILURE;
    }


	ifstream iFile;

	char* iFileName = "/etc/printers/epijs.cfg"; 
	iFile.open(iFileName, ios::binary);
	if(!iFile.is_open())
	{
		cout << "Error opening input file named: " << iFileName << endl;
		exit (1); 
	}
	
	int wcount;
	while(!iFile.eof())
	{
		char buffer[132];
		iFile.read(buffer, 132);
		wcount=iFile.gcount();
		if (write(serf, buffer, wcount) != wcount)
		{
			cout << "Write error!" << endl;
			exit (1);
		};
	}
	
	iFile.close();
	close(serf);
	
	return EXIT_SUCCESS;
}