kbd_write
kbd_write(s->keys2, f2, 0, s->vkbd);
kbd_write(s->keys1, f1, 1, s->vkbd);
kbd_write(diff, f2, 0, s->vkbd);
kbd_write(s->keys1, f1, 1, s->vkbd);
static void kbd_write(bitstr_t *m, int32_t fb, int32_t make, int32_t fd);