Not able to open device (in dynamic mode)

[SteMMo33]

Hi all, I wrote a simple app to send data to LED strip device. Using the library statically linked there are no problems. Then I wrote another program with the library dynamically linked. The device is not opened. This is my code:

`

   lwsl_user("Devices:\n");
struct hid_device_info* pInfo = pHidEnumerate( 0, 0);
if (pInfo){
    struct hid_device_info* p = pInfo;
    while(p){
        lwsl_user("> %04X:%04X '%s' '%S' '%s'\n", p->vendor_id, p->product_id, p->path, p->manufacturer_string, p->product_string);
        p = p->next;
    }
}
else
    lwsl_user("- empty\n");
// hid_free_enumeration(pInfo);
// Open the device using the VID, PID,
// and optionally the Serial number.
wchar_t sn[80]={0};
handle = pHidOpen(0x20A0, 0x41E5, sn);
lwsl_user("fnOpen=%p sn='%S'\n", pHidOpen, sn);
if (handle==0){
    lwsl_user(".. Device not found\n");
    return CMDRET_ERR;
}   
lwsl_user("> device handle: %X\n", handle);
return CMDRET_OK;

`

This is the output:

`

Pointers ok. Open device .. hid_init: 0 Lista devices: 20A0:41E5 '0001:0027:00' '(null)' '(null)' 14C8:0005 '0001:0003:00' '(null)' '(null)' 0BDA:481A '0003:0002:ff' '(null)' '(null)' fnOpen=0xb5dcda39 sn='' .. Device not found closeLedStrip handle=0 hLibrary=80848690 ` The device is enumerated but not opened. Any idea?

Thanks, regards

[SteMMo33]

Sorry, not correct. I linked statically and I have the same problem. If I run other app on the same machine it works o_O Almost the same code .. Both of them enumerate the HID devices and both try to open the same VID + PID (included in the enumerated devices).

handle = hid_open(0x20A0, 0x41E5, NULL);

The outpus are:

hid_init: 0 Lista HID devices: 062A:4101 'MOSART Semi.' '2.4G Keyboard Mouse' 062A:4101 'MOSART Semi.' '2.4G Keyboard Mouse' 20A0:41E5 'Agile Innovative Ltd' 'BlinkStick' 14C8:0005 'Zytronic Displays Limited' 'Zytronic Touchscreen Controller' 0BDA:481A 'Generic' 'USB Audio' open handle: 81330680 Manufacturer String [res:0]: Agile Innovative Ltd

vs

hid_init: 0 Lista HID devices: 062A:4101 062A:4101 20A0:41E5 14C8:0005 0BDA:481A open handle: 0 .. Device not found

I compiled the hidtest app and I had similar result about the enumeration: it is able to open the device.

Any idea?

[Youw]

What platform is it? (Linux?) Did you perform hid_init first?

In any case, I think you should already have a solution: you have a working application - simply check what is the difference.

[SteMMo33]

Yes, the platform is ASUS Tinkerboard with Linaro (Debian for ARM). Yes, i performed hid_init and the row

hid_init: 0

is the return code. The code (apart the debug strings) is the same :(

[Youw]

BTW: consider updating to a new version. See #373.

[SteMMo33]

Discovered the problem! The applications was run by root; instead the application that did not work is launched by www-data user. Is there a way to allow to www-data user to open the device?

[Youw]

That is a general UNIX question, e.g.: https://unix.stackexchange.com/questions/172197/give-group-permissions-to-specific-device