How to use force feedback correctly?

How to use force feedback correctly?

[Alexander Stein]

Hello,

I've read the documentation about force feedback in 
Documentation/input/ff.txt. But I'm rather unsure how to use it actually. So 
far I understood this you have to use /dev/input/eventX to access your ff-
device. But normally only root has read and write access to this device files, 
while a joystick is used normally using /dev/input/jsX which can be used by a 
non-root user.

So my actual question is: How can I use force feedback of a joystick without 
setting global read/write permissions to /dev/input/eventX? Or may I even be 
able to use force feedback using /dev/input/jsX?

Other thing: Is it possible that on line 52 in Documentation/input/ff.txt the 
declaration of the features array is wrong?
> #52 unsigned long features[1 + FF_MAX/sizeof(unsigned long)];
IMO it has to be declared like this:
> unsigned long features[1 + FF_MAX/ (8 * sizeof(unsigned long))];
Which creates actually a Bit array, not an Byte array.

Thanks in advance
Regards
Alexander

Re: How to use force feedback correctly?

[Anssi Hannula]

Alexander Stein wrote:
> Hello,

Hi!

> I've read the documentation about force feedback in 
> Documentation/input/ff.txt. But I'm rather unsure how to use it actually. So 
> far I understood this you have to use /dev/input/eventX to access your ff-
> device. But normally only root has read and write access to this device files, 
> while a joystick is used normally using /dev/input/jsX which can be used by a 
> non-root user.
> 
> So my actual question is: How can I use force feedback of a joystick without 
> setting global read/write permissions to /dev/input/eventX?

The distribution should configure joystick eventX devices to
either have global read/write access, or read/write access for one group
(which the user is in), or have it chown the device to logged-in user,
depending on distribution conventions.

One can identify joystick devices from other eventX devices with udev
variable ENV{ID_CLASS}="joystick", or with existence of
"/dev/input/by-path/*-event-joystick", which is a symlink to the eventX
device.

On Mandriva Linux, permissions are granted to logged-in user with
pam_console / ConsoleKit, with /dev/input/by-path/*-event-joystick.

> Or may I even be 
> able to use force feedback using /dev/input/jsX?

Nope.

> Other thing: Is it possible that on line 52 in Documentation/input/ff.txt the 
> declaration of the features array is wrong?
>> #52 unsigned long features[1 + FF_MAX/sizeof(unsigned long)];
> IMO it has to be declared like this:
>> unsigned long features[1 + FF_MAX/ (8 * sizeof(unsigned long))];
> Which creates actually a Bit array, not an Byte array.

Right, seems to be wrong.

-- 
Anssi Hannula

Re: How to use force feedback correctly?

[Dmitriy Geels]

2009/3/17 Anssi Hannula <anssi.hannula@gmail.com>:
>> So my actual question is: How can I use force feedback of a joystick without
>> setting global read/write permissions to /dev/input/eventX?
>
> The distribution should configure joystick eventX devices to
> either have global read/write access, or read/write access for one group
> (which the user is in), or have it chown the device to logged-in user,
> depending on distribution conventions.
>
> One can identify joystick devices from other eventX devices with udev
> variable ENV{ID_CLASS}="joystick", or with existence of
> "/dev/input/by-path/*-event-joystick", which is a symlink to the eventX
> device.
Created bug report for ubuntu jaunty. https://bugs.launchpad.net/bugs/344673
This wasn't a problem for ubuntu, because kernels prior to 2.6.28 were
missing force feedback support for hid devices.
You can make this rule yourself, here is a good manual:
http://www.reactivated.net/writing_udev_rules.html
Or just wait, I will make this rule and post it to bug report.