When there are no such events, keyboard_update() returns 0 immediately (non-zero else) whereas keyboard_waitforupdate() blocks and waits until an event occurs.
vga_waitevent(3) allows to wait for keyboard and other events at the same time.
svgalib(7), vgagl(7), libvga.config(5), keytest(6), eventtest(6), keyboard_seteventhandler(3), keyboard_init(3), keyboard_init_return_fd(3), keyboard_close(3), keyboard_setdefaulteventhandler(3), keyboard_getstate(3), keyboard_clearstate(3), keyboard_translatekeys(3), keyboard_keypressed(3), vga_waitevent(3)
This manual page was edited by Michael Weller <email@example.com>. The exact source of the referenced function as well as of the original documentation is unknown.
It is very likely that both are at least to some extent are due to Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby asked to be excused by the original author and will happily accept any additions or corrections to this first version of the svgalib manual.