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