From: Phil Callihan <pcallihan@...>
Date: 2003-12-21T14:16:53+09:00
Subject: Ioctl problem

I'm trying to use Ruby IO:ioctl on /dev/mixer.  It work with c but not 
with ruby.  I sure it a dumb mistake, but I can see it.  Below is a ruby 
program that fails and the c program that work.  Thanks ahead of time.
pc
_________
#! /usr/bin/env ruby

SOUND_MIXER_READ_DEVMASK = 0x80044dfe

mixer = File.open("/dev/mixer", "w+")
notused = 0
devmask = mixer.ioctl(SOUND_MIXER_READ_DEVMASK, notused)
printf "devmask[%08x]\n", devmask

#~ Program results:
#~ test.rb:8:
#~ in `ioctl': Bad address - /dev/mixer (Errno::EFAULT) from test.rb:8
__________
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>

#define SOUND_MIXER_READ_DEVMASK 0X80044dfe

int main(int argc, char *argv[])
{
	int mixerfd, devmask;
	
	char* name = "/dev/mixer";
	if ((mixerfd = open(name, O_RDWR)) < 0) {
		perror(name);
		exit(1);
	}
	if (ioctl(mixerfd, SOUND_MIXER_READ_DEVMASK, &devmask) == -1) {
		perror("SOUND_MIXER_READ_DEVMASK");
		exit(-1);
	}
	printf("Mixer Device mask [%08x]\n", devmask);

	return 0;
}
/*
Program results:
Mixer Device mask [005051d1]
*/