I'm attempting to read the name, vendor ID and product ID for a USB joystick on Ubuntu (specifically I'm working with a wired Xbox 360 pad on Ubuntu 13.10 x64). I can read the name but when attempting to read the vendor and product IDs I get an EINVAL error. The code is as follows:
if (plugged[index])
{
char name[32];
std::snprintf(name, sizeof(name), "/dev/input/js%u", index);
// Open the joystick's file descriptor (read-only and non-blocking)
m_file = ::open(name, O_RDONLY | O_NONBLOCK);
if (m_file >= 0)
{
// Retrieve the axes mapping
ioctl(m_file, JSIOCGAXMAP, m_mapping);
// Get the name
char joyname[128];
if (ioctl(m_file, JSIOCGNAME(128), joyname) < 0) {
m_name = "Unknown Joystick";
} else {
m_name = joyname;
}
// Get vendor and product IDs
input_id inpid;
if (ioctl(m_file, EVIOCGID, &inpid) < 0) {
if (errno == EBADF) printf("EBADF\n");
if (errno == EFAULT) printf("EFAULT\n");
if (errno == ENOTTY) printf("ENOTTY\n");
if (errno == EINVAL) printf("EINVAL\n");
m_manufacturerID = 0;
m_productID = 0;
} else {
m_manufacturerID = inpid.vendor;
m_productID = inpid.product;
}
// Reset the joystick state
m_state = JoystickState();
return true;
}
else
{
return false;
}
}
else
{
return false;
}
The snippet that reads vendor and product IDs is:
ioctl(m_file, EVIOCGID, &inpid)
According the man page for ioctl, EINVAL the request (EVIOCGID) or argp (inpid) is invalid.
How can I determine which is invalid?
After doing some more digging I found that the reason ioctl(m_file, EVIOCGID, &inpid) fails is that the device I'm opening is a joystick (/dev/input/js) and the EVIOCGID ioctl is for event devices (/dev/input/event) hence the failure. Unfortunately there is not JSIOCGID ioctl so I had to change tactics. Instead I'm using udev to access the joystick's vendor and product IDs. Here's the code I'm using:
// Use udev to look up the product and manufacturer IDs
struct udev *udev = udev_new();
if (udev)
{
char sysname[32];
std::snprintf(sysname, sizeof(sysname), "js%u", index);
struct udev_device *dev = udev_device_new_from_subsystem_sysname(udev, "input", sysname);
dev = udev_device_get_parent_with_subsystem_devtype(dev, "usb", "usb_device");
if (!dev)
{
err() << "Unable to find parent USB device" << std::endl;
}
std::stringstream ss;
ss << std::hex << udev_device_get_sysattr_value(dev, "idVendor");
ss >> m_manufacturerID;
ss.clear();
ss.str("");
ss << std::hex << udev_device_get_sysattr_value(dev, "idProduct");
ss >> m_productID;
udev_device_unref(dev);
udev_unref(udev);
}
else
{
err() << "Cannot create udev" << std::endl;
}
With udev I've been able to consistently retrieve vendor and product IDs for USB joysticks on Ubuntu 13.10 x64.
UPDATE
I've tested this further with:
In all instances this code worked great.