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From:   John Salamon <salamonj9@gmail.com>
Date:   Wed, 11 Oct 2023 17:10:09 +1030
Message-ID: <CA+fyA4Qsm6ydyxNQL4cLak+1eNYBvOJzJwonts84YTavBKB8vg@mail.gmail.com>
Subject: Re: uinput: waiting for UI_FF_UPLOAD events will not inform user when
 allocation is required
To:     dmitry.torokhov@gmail.com, rydberg@bitmath.org
Cc:     linux-input@vger.kernel.org, linux-kernel@vger.kernel.org
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Correction, "old" is a pointer to struct ff_effect, which after being
set to NULL looks like it gets pushed out by uinput on a struct
uinput_request.


On Tue, Oct 10, 2023 at 5:38=E2=80=AFPM John Salamon <salamonj9@gmail.com> =
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.
>
> 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 =3D=3D NULL to know when allocations are needed
> I think uinput documentation should describe this.
>
> I first noticed this using python-evdev, see my issue report here:
> https://github.com/gvalkov/python-evdev/issues/199