Linux force feedback hello world

gistfile1.txt

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

#include <linux/input.h>

#include <stdint.h>

#include <stdio.h>
#include <assert.h>

#define FF_EFFECTS(FX) \
    FX(FF_RUMBLE) \
    FX(FF_PERIODIC) \
    FX(FF_CONSTANT) \
    FX(FF_SPRING) \
    FX(FF_FRICTION) \
    FX(FF_DAMPER) \
    FX(FF_INERTIA) \
    FX(FF_RAMP) \
    FX(FF_SQUARE) \
    FX(FF_TRIANGLE) \
    FX(FF_SINE) \
    FX(FF_SAW_UP) \
    FX(FF_SAW_DOWN) \
    FX(FF_CUSTOM)

#define GETBIT(mask, bit) \
    ((((uint8_t*)(mask))[(bit) / 8] & (1 << ((bit) % 8))) != 0)

static void test_joystick(const char *path) {
    int err = 0;
    int fd = open(path, O_RDWR);
    if(fd == -1) {
        fprintf(stderr, "Can't open %s: %s\n", path, strerror(errno));
        return;
    }

    const int max_name_len = 128;
    char dev_name[max_name_len];
    int name_len = ioctl(fd, EVIOCGNAME(max_name_len), dev_name);
    if(name_len < 0) {
        fprintf(stderr, "Can't get device name %s: %s\n", path, strerror(errno));
        goto fail;
    }

    printf("device name: %s\n", dev_name);

    uint8_t ff_bits[(FF_CNT + 7) / 8];
    err = ioctl(fd, EVIOCGBIT(EV_FF, sizeof(ff_bits)), ff_bits);
    assert(err >= 0);

#define printit(x) \
    if(GETBIT(ff_bits, x)) printf("%s\n", #x);

    FF_EFFECTS(printit);

    struct ff_effect fx;
    fx.type = FF_RUMBLE;
    fx.id = -1;
    fx.direction = 0x0;

    fx.trigger.button = 0;
    fx.trigger.interval = 0;

    fx.replay.length = 500;
    fx.replay.delay = 0;

    fx.u.rumble.strong_magnitude = 0x2000;
    fx.u.rumble.weak_magnitude = 0x2000;

    err = ioctl(fd, EVIOCSFF, &fx);
    assert(err >= 0);

    printf("new fx id: %d\n", fx.id);

    struct input_event play;
    play.type = EV_FF;
    play.code = fx.id;
    play.value = 3;

    write(fd, (const void*)&play, sizeof(play));

    sleep(5);

fail:
    close(fd);
}

int main(int argc, char *argv[]) {
    (void)argc; (void)argv;

    test_joystick("/dev/input/event16");

    return 0;
}