Hello! I'm currently writing an Xbox One controller driver for Linux, however I have come across an issue that I seem to not be able to resolve. In my open syscall below, I'm calling the usb_control_msg() function, in order to get a status update from my device. However, when I access the open syscall in my user-space program, perror returns an error of "Invalid argument". When i check dmesg, I see lots of warnings / errors, yet the usb_control_msg() function still returns a positive number, thus indicating that bytes were successfully transferred to my buffer. Could you please help me out?

Also, when I attempt to print my data buffer, it prints as NULL, even though two bytes were transferred to my data buffer. I'm attempting to print the data buffer with "printk(KERN_INFO "Data: %*phC", data);"

Code:

static int xb1_open(struct inode *inode, struct file *file) {
    printk(KERN_INFO "open function called..");

    struct xb1_controller *dev;
    struct usb_interface *interface;
    int subminor;
    int retval = 0;

    subminor = iminor(inode);

    interface = usb_find_interface(&xb1_driver, subminor);
    if(!interface) {
        printk(KERN_INFO "Unable to locate interface in open  
                  function");
        retval = -ENODEV;
        goto exit;
    }

    dev = usb_get_intfdata(interface);
    if(!dev) {
        printk(KERN_INFO "Unable to locate dev structure in open 
                  function");
        retval = -ENODEV;
        goto exit;
    }

    char data[8];
    memset(&data, 0, sizeof(data));

    retval = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev,   
                  0), USB_REQ_GET_STATUS, USB_DIR_IN, 0, 0, 
                  &data, sizeof(data), 0);
    if(retval < 0) {
        printk(KERN_INFO "usb_control_msg failed | Retval = %d", 
                  retval);
    }
    else {
         printk(KERN_INFO "Retval: %d", retval);
    }

In the below dmesg output, you can see that Retval is assigned a value of 2 (second line):

[ 77.102749] open function called.. [ 77.122795]

Retval: 2

[ 77.123087] ------------[ cut here ]------------ [ 77.123107] WARNING: CPU: 0 PID: 2278 at /build/linux-kOWph6/linux-4.4.0/fs/namei.c:3215 path_openat 0xb19/0x1330()

[ 77.123108] Modules linked in: xpad ff_memless main(OE) snd_intel8x0 snd_ac97_codec ac97_bus crct10dif_pclmul crc32_pclmul snd_pcm snd_seq_midi snd_seq_midi_event vboxvideo aesni_intel aes_x86_64 ttm lrw snd_rawmidi gf128mul drm_kms_helper glue_helper ablk_helper cryptd snd_seq drm snd_seq_device snd_timer joydev input_leds snd fb_sys_fops syscopyarea sysfillrect serio_raw sysimgblt soundcore vboxguest i2c_piix4 mac_hid 8250_fintek parport_pc ppdev lp parport autofs4 hid_generic usbhid hid psmouse ahci libahci e1000 pata_acpi video fjes

[ 77.123152] CPU: 0 PID: 2278 Comm: hello Tainted: G OE 4.4.0-45-generic #66-Ubuntu

[ 77.123154] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006

[ 77.123156] 0000000000000286 000000005d6bd96b ffff8800d980bcb8 ffffffff813f1fe3

[ 77.123159] 0000000000000000 ffffffff81cd8e58 ffff8800d980bcf0 ffffffff81081212

[ 77.123162] ffff8800d980bdd0 0000000000008002 ffff8800d980bef4 00000000ffffffea

[ 77.123165] Call Trace:

[ 77.123172] [] dump_stack 0x63/0x90

[ 77.123177] [] warn_slowpath_common 0x82/0xc0

[ 77.123180] [] warn_slowpath_null 0x1a/0x20

[ 77.123183] [] path_openat 0xb19/0x1330

[ 77.123187] [] do_filp_open 0x91/0x100

[ 77.123191] [] ? rawcallee_save__pv_queued_spin_unlock 0x11/0x20

[ 77.123194] [] ? __alloc_fd 0xc8/0x190

[ 77.123198] [] do_sys_open 0x138/0x2a0

[ 77.123201] [] ? __do_page_fault 0x1b4/0x400

[ 77.123204] [] SyS_open 0x1e/0x20

[ 77.123213] [] entry_SYSCALL_64_fastpath 0x16/0x71

[ 77.123216] ---[ end trace a1ba30f9590f2a36 ]---