Hi John, On Tue, Oct 10, 2023 at 05:38:27PM +1030, John Salamon wrote: > Currently the "fake" input events generated by uinput in response to > effect uploads will return an effect with an id that has already been > handled by input_ff_upload in ff-core.c, which can modify the effect > id. This causes a problem specifically when the effect originally > uploaded via the EVIOCSFF ioctl contained an effect with -1, as the > userspace code handling UI_FF_UPLOAD receives an effect with an id > other than -1, and therefore will not know an allocation was > requested. The kernel never changes ID of an existing effect, the only time ID is changed is when userspace indicates that a new effect should be created by setting effect ID to -1. The handler of force feedback effects should know what effects (with what IDs) have been uploaded to the device so far, so whenever it sees a request for an effect with previously unseen effect_id it should recognize this as a signal that a new effect/id has been allocated by the kernel. > > I notice that the "old" field on the ff_effect struct is set to NULL > when the -1 id is changed (in input_ff_upload), which can serve as a > flag that an allocation was requested. If it is the intention is that > uinput users check if old == NULL to know when allocations are needed > I think uinput documentation should describe this. No, not really, as explained above. > > I first noticed this using python-evdev, see my issue report here: > https://github.com/gvalkov/python-evdev/issues/199 Thanks. -- Dmitry
