ioctl - does it actually work? replaced or preferred by something else?

Jack B. Nymbol has asked for the wisdom of the Perl Monks concerning the following question:

Playing with some ioctl but not having any success. This is supposed to turn off the CAPS-LOCK LED. I'm starting to think that maybe ioctl is out of favor and therefore not well supported. I ran h2ph -r -l -h . in /usr/include. I even came across something called h2pl but it appears to be vestigial.

require 'sys/ioctl.ph';
sysopen( FD, "/dev/console", 1 ) or die "Unable to open /dev/console";
select(FD);$|++;
my $KDSETLED = 0x4B32;
my $stat = ioctl(FD, $KDSETLED, 0x0) || -1;
close(FD);

print STDOUT "status = $stat\n";
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Re: ioctl - does it actually work? replaced or preferred by something else? by Khen1950fx (Canon) on Feb 19, 2007 at 03:04 UTC
It worked for me. It turned off CAPS-LOCKED and returned `Status = 0 but true`.	[reply] [d/l]
Re: ioctl - does it actually work? replaced or preferred by something else? by zentara (Cardinal) on Feb 19, 2007 at 14:20 UTC
It worked for me too, but only as root. When running it as a user I get the error "Unable to open /dev/console". What errors or malfunction do you see? I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]
Re^2: ioctl - does it actually work? replaced or preferred by something else? by Jack B. Nymbol (Acolyte) on Feb 19, 2007 at 18:25 UTC
Yes, works as root, as user it doesn't work. The perms allow user access to /dev/console. Running in perl -d I can print FD "\a" and hear the bell. Since the user has permission for the device I don't understand what's preventing this. As for turning the LED back on, use your keyboard.	[reply]
Re^3: ioctl - does it actually work? replaced or preferred by something else? by zentara (Cardinal) on Feb 19, 2007 at 18:33 UTC
I'm running a grsecurity kernel, and it does some things to limit users access to /dev/console for security reasons. As far as using the keyboard to reset the led, it dosn't. On my system, if I run the script I can turn off or turn on the led, but after I exit the script, the light no longer functions, when I toggle the Caps Lock key. It may be all because of my security kernel, but it's a fairly common patch people are using. I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]
Re^4: ioctl - does it actually work? replaced or preferred by something else? by Jack B. Nymbol (Acolyte) on Feb 19, 2007 at 20:12 UTC
Re^5: ioctl - does it actually work? replaced or preferred by something else? by zentara (Cardinal) on Feb 19, 2007 at 21:54 UTC
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Re: ioctl - does it actually work? replaced or preferred by something else? by zentara (Cardinal) on Feb 19, 2007 at 15:11 UTC
Yikes, I found another glitch. As root, your script turns off the caps-lock-led, BUT..... it stays off. You wouldn't know how to turn it back on would you? :-) I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]
Re^2: ioctl - does it actually work? replaced or preferred by something else? by Fletch (Bishop) on Feb 19, 2007 at 18:14 UTC
There's a Lovecraft-ian quote which comes to mind, the gist of which is not calling forth that which you don't know how to send back; similar precaution should probably be applied when poking around with ioctls (and especially doing so as root :)	[reply]
Re^3: ioctl - does it actually work? replaced or preferred by something else? by zentara (Cardinal) on Feb 19, 2007 at 18:19 UTC
Yeah, it took a reboot to clear it. The code above not only sets the LED, but screws up the keyboard LED flags. Its all in /usr/include/linux/kd.h , but resetting the flag to normal working order is not obvious. A logout/login did not reset it, only a reboot did. I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]