On Tue, Apr 21, 2020 at 11:53:19AM -0700, Brendan Shanks wrote: > > > On Nov 27, 2019, at 2:10 AM, Mathieu Maret <mathieu.maret@xxxxxxxxx> > > wrote: > > > > Hi, > > > > I'm using evdev for vibrator interface. I can register ff_effect > > and play them. But, if I do any kind of fork, all the effects are > > flush and cannot be used. > > > > You can find, below, an example of such a program. From some trace > > have put in the kernel, it's seems that at the end of the system() > > call, evdev_flush get called. > > > > evdev_flush() will call flush_effects() that will remove all the > > registered effects. > > > > I've only one device with vibrator and it's a imx6 4.1.15 kernel. > > But code looks the same that in linus master that why I'm posting it > > here. I hope that it will not waste people time > > > > Hi everyone, > > I’m also hitting this bug with games that use force-feedback steering > wheels under Wine/Proton. It typically shows up as EVIOCSFF ioctls > failing with EINVAL, since all the effects were unexpectedly flushed. > > The problem is that input_ff_flush() is called whenever a file > descriptor is closed, but there can be multiple descriptors open to > the same file description (through fork(), dup(), etc). > input_ff_flush() removes all effects added by that file description, > which the users of the other descriptors certainly don't expect. > > As for the fix, maybe fd_ops->flush() shouldn’t be implemented at all? > In the current design, effects “belong” to a file description (a > struct file *), not a descriptor. This seems sensible to me: a process > could open a device, upload an effect, then fork(), and it makes sense > that the child would have full control of the effects created by the > parent. It seems to me like nothing should be done when a descriptor > is closed, and input_ff_flush() should be called only when the whole > struct file is released. > Yes, I agree, we should drop setting fops->flush and move the code into evdev_release(). This will ensure that the effects are stopped and erased once file is closed, but will allow passing the descriptors around. Can I get a real patch for this please? Thanks. -- Dmitry
