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Linux:试图通过ioctl获取操纵杆供应商和产品ID,取而代之的是EINVAL

作者:互联网

我试图在Ubuntu上读取USB操纵杆的名称,供应商ID和产品ID(特别是我在Ubuntu 13.10 x64上使用有线Xbox 360打击垫).我可以读取名称,但在尝试阅读供应商和产品ID时,我收到EINVAL错误.代码如下:

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;
}

读取供应商和产品ID的代码段是:

ioctl(m_file, EVIOCGID, &inpid)

根据man page for ioctl,EINVAL请求(EVIOCGID)或argp(inpid)无效.

如何确定哪个无效?

解决方法:

在做了一些挖掘之后,我发现ioctl(m_file,EVIOCGID和& inpid)失败的原因是我打开的设备是操纵杆(/ dev / input / js)而EVIOCGID ioctl是用于事件设备(/ dev / input / event)因此失败了.不幸的是,没有JSIOCGID ioctl所以我不得不改变策略.相反,我使用udev来访问操纵杆的供应商和产品ID.这是我正在使用的代码:

// 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;
}

使用udev,我能够在Ubuntu 13.10 x64上一致地检索USB游戏杆的供应商和产品ID.

UPDATE

我进一步测试了这个:

> Linux Mint 16 x64
> Manjaro x64
> Fedora 20 x64

在所有情况下,这段代码都很有效.

标签:ioctl,joystick,linux,ubuntu,usb
来源: https://codeday.me/bug/20190728/1564021.html