CODEWITHSUNDEEP
c++clibusblibeventlibusb-1.0
Pawel Zubrycki
Pawel Zubrycki

Reputation: 2713

How to use libusb with libevent?

I'm writing an event-driven application using libevent, and I need to do a USB transfer using libusb-1.0.

I wanted to use libusb_get_pollfds to get a list of files descriptors (in fds) and add them to libevent like this:

const struct libusb_pollfd **fds = libusb_get_pollfds(device->context);

const struct libusb_pollfd *it = *fds;
for(;it != NULL; ++it) {
    cout << "Adding fd: " << it->fd << ", " << it->events << endl;
    struct event * ev = event_new(base_, 
        it->fd, it->events | EV_PERSIST, 
        callbacks::libusb_cb, this);
    event_add(ev, 0);
    libusb_fds_events.insert(std::make_pair(it->fd, ev));
}

free(fds);

// (...)

// And the callback function:
void callbacks::libusb_cb(evutil_socket_t fd, short what, void *arg) {
    Server *s = reinterpret_cast<Server*>(arg);
    libusb_handle_events_timeout(s->device_->context, 0);
}

Also, I use libusb_set_pollfd_notifiers to add/remove fds from libusb_fds_events.

The problem is I get many strange fds on the list returned by libusb (for example, I get stdin(!) many times with event equals to 0).

Am I using it in right way?

Upvotes: 3

Views: 3052

Answers (1)

Pawel Zubrycki
Pawel Zubrycki

Reputation: 2713

I found an error in code. It should have been:

const struct libusb_pollfd **it = fds;
for(;*it != NULL; ++it) {
    cout << "Adding fd: " << (*it)->fd << ", " << (*it)->events << endl;
    struct event * ev = event_new(base_, 
        (*it)->fd, (*it)->events | EV_PERSIST, 
        callbacks::libusb_cb, this);
    event_add(ev, 0);
    libusb_fds_events.insert(std::make_pair((*it)->fd, ev));
}

Upvotes: 5

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