xlockkbd.c


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#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/keysym.h>

static void die(const char *s)
{
	fprintf(stderr, "xlockkbd: %s\n", s);
	exit(1);
}

static bool grab_kbd(Display *d, int screen)
{
	Window w = RootWindow(d, screen);
	int res;

	// attempt to grab keyboard for 500ms if already grabbed.
	// thanks to slock code for the pointer.
	for (int i = 0;;) {
		res = XGrabKeyboard(d, w, True, GrabModeAsync, GrabModeAsync,
			CurrentTime);
		if (res != AlreadyGrabbed || ++i > 5)
			break;

		usleep(100000);
	}

	return (res == GrabSuccess);
}

static void wait_for_key(Display *d)
{
	XEvent ev;
	while (!XNextEvent(d, &ev)) {
		if (ev.type == KeyPress &&
				XLookupKeysym(&ev.xkey, 0) == XK_Escape)
			break;
	}
}

int main()
{
	Display *d = XOpenDisplay(NULL);
	if (!d)
		die("cannot open display");

	for (int i = 0; i < ScreenCount(d); ++i) {
		if (!grab_kbd(d, i))
			die("failed to grab keyboard");
	}

	wait_for_key(d);
	return 0;
}