[libhid-discuss] hid_force_open failed with return code 12

[Charles Lepple]

Marius Scurtescu wrote:
> On 3/21/07, Charles Lepple <clepple at ghz.cc> wrote:
>> On Mar 20, 2007, at 10:34 PM, Marius Scurtescu wrote:
>>
>> > Hi,
>> >
>> > I am using libhid under Ubuntu Edgy, tried both i386 and amd64
>> > (0.2.15+20060325-2ubuntu1).
>> >
>> > Trying to access a Radio Shark 2 device. The problem is that libhid
>> > cannot detach the kernel driver from the USB device.
>> >
>> > Using libhid-detach-device, same thing.
>> >
>> > Any suggestions?
>>
>> The most common problem is not having write permission to the device
>> node in /dev/bus/usb/*/*.
>
> That must be it. If I am running as root then it detaches fine. Only
> root has write access to these devices. How can I change this? Should
> I change the group or force write for all?
>
> Also, the device gets created when you insert the USB connector, can
> you control permissions on that?

You can do something like what we have in Network UPS Tools for USB UPSes:

http://boxster.ghz.cc/projects/nut/browser/trunk/scripts/udev/nut-usbups.rules.in

I think the README file one level up has some info on installing the udev
rules file. (Note that the autoconf script would take the
nut-usbups.rules.in file and replace @RUN_AS_GROUP@ with the actual
configured group, writing the output to nut-usbups.rules. Your udev script
could do something similar with your userid instead of the group.)

-- 
Charles Lepple
clepple at ghz.cc