I really love the Magic SysRq key. It's always nice to know that you can do some emergency actions even when the system is 99% locked up. What's my favorite sequence? Probably 'subo'. I'm still figuring it out.
One of my beefs with MSRK is that sometimes I can't be sure if it is responding (am I pressing the right sequence?). This usually happens when I get a crash while in X, not seeing the console.
I wrote a small kernel module to add a new action to the Magic SysRq key. The new action's, "Visualize", only purpose is to give back a cue that it's listening.
I copied from some kernel hacking example code for blinking the keyboard leds (should be possible if the kernel still reads commands from the keyboard) and for beeping (although I haven't got that working yet).
First try is using timers ('add_timer'). This seems to be working nicely on lappy but inconsistently on blackbird (sometimes the leds don't light up and sometime they light up but don't go off). I'm pretty sure that the timer function gets called because I can see the printk's. I guess this means that the IOCTL is failing. I'll try replacing the timer with work queue, see if that helps.
P.S.: Another difference between lappy and blackbird: On blackbird the 'v' from the Alt-SysRq-V sequence gets swallowed, whily on lappy it gets printed. Strange.
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