From: Phil Callihan <callihan@...>
Date: 2003-12-21T14:26:54+09:00
Subject: Trouble using IO::ioctl

I'm trying to write a audio volume control with Ruby.  I want to use
Ruby's ioctl method to control the mixer.  It's just not working. Here
is two short program to demonstrate the problem.  It has to be a dumb
mistake, but I don't see it.  Thanks ahead of time.

pc

Ruby program fails:
___________________________________________
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
_____________________________________________
C program works:
#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]
*/