Re: uinput: ioctls for UI_BEGIN_FF_UPLOAD fails (returns -1). How to debug?

2016-03-27 20:53 GMT+02:00 Manuel Reimer [off-list ref]:

Hello,

I'm writing on an usermode input driver.

Currently my force feedback support just consists of some printf's as a
first try.

My problem is, that it seems like as soon as I first sent something to my
open uinput device (some buttons that were pressed on the device) the uinput
backend seems to get into some bad state.

My "force feedback thread" gets the "EV_UINPUT" event trigger, but if I try
to call

ioctl(args->fduinput, UI_BEGIN_FF_UPLOAD, &upload);

in this case, then the return value is "-1"...

Check the value of errno just after the failed call (and use strerror
to get a nice error message).

The same code works without any problem if no buttons are pressed and
"fftest" is called directly after startup of the driver application.

Can someone help me with debugging this problem? My understanding is, that
this call shouldn't return -1 if the "EV_UINPUT" event was successfully
received, right?

You also need to check the event code, it must be UI_FF_UPLOAD.

My system:

$ uname -a
Linux manuelspc 4.4.5-1-ARCH #1 SMP PREEMPT Thu Mar 10 07:38:19 CET 2016
x86_64 GNU/Linux

Thank you very much in advance.

Manuel
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