Interested in learning OS-level programming

[kqlnut]

The flashlight, along with many other things, is controlled by reading and writing 'files' under the /sys pseudo-filesystem. You can do that using normal shell tools like echo, tee, pipes etc. or by using a programming language's file read/write methods. In this case you're looking to write either 0 or 1 to /sys/devices/platform/led-controller/leds/white:flash/brightness - note the permissions on that file which may mean you'll need to use sudo or similar to access it.

Just noticed this very informed response. I don't suppose this kind of stuff is documented anywhere? And is it OS specific? I can RTFM if I can find them.

You can find a lot of that very helpful stuff on megous' website, very informative (scroll down to the feature/driver support matrix and click on the part that interests you). It should not depend on the OS as long as they are using a similar kernel.