lkml.org 
[lkml]   [2015]   [Oct]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 1/2] Input: Document and check on implicitly defined FF_MAX_EFFECTS
    On Thu, Sep 17, 2015 at 07:29:47PM +0200, Elias Vanderstuyft wrote:
    > There is an undocumented upper bound for the total number of ff effects:
    > FF_GAIN (= 96).
    > This can be found as follows:
    > - user: write(EV_FF, effect_id, iterations)
    > calls kernel: ff->playback(effect_id, ...): starts effect "effect_id"
    > - user: write(EV_FF, FF_GAIN, gain)
    > calls kernel: ff->set_gain(gain, ...): sets gain
    >
    > A collision occurs when effect_id equals FF_GAIN.
    > According to input_ff_event(),
    > FF_GAIN is the smallest value where a collision occurs.
    > Therefore the greatest safe value for effect_id is FF_GAIN - 1,
    > and thus the total number of effects should never exceed FF_GAIN.
    >
    > Define FF_MAX_EFFECTS as FF_GAIN and check on this limit in ff-core.
    >
    > Signed-off-by: Elias Vanderstuyft <elias.vds@gmail.com>

    Applied, thank you.

    > ---
    > drivers/input/ff-core.c | 5 +++++
    > include/uapi/linux/input.h | 8 ++++++++
    > 2 files changed, 13 insertions(+)
    >
    > diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c
    > index c642082..0bf7008 100644
    > --- a/drivers/input/ff-core.c
    > +++ b/drivers/input/ff-core.c
    > @@ -318,6 +318,11 @@ int input_ff_create(struct input_dev *dev, unsigned int max_effects)
    > return -EINVAL;
    > }
    >
    > + if (max_effects > FF_MAX_EFFECTS) {
    > + dev_err(&dev->dev, "cannot allocate more than FF_MAX_EFFECTS effects\n");
    > + return -EINVAL;
    > + }
    > +
    > ff_dev_size = sizeof(struct ff_device) +
    > max_effects * sizeof(struct file *);
    > if (ff_dev_size < max_effects) /* overflow */
    > diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
    > index 63915a7..42d7933 100644
    > --- a/include/uapi/linux/input.h
    > +++ b/include/uapi/linux/input.h
    > @@ -1200,6 +1200,14 @@ struct ff_effect {
    > #define FF_GAIN 0x60
    > #define FF_AUTOCENTER 0x61
    >
    > +/*
    > + * ff->playback(effect_id = FF_GAIN) is the first effect_id to
    > + * cause a collision with another ff method, in this case ff->set_gain().
    > + * Therefore the greatest safe value for effect_id is FF_GAIN - 1,
    > + * and thus the total number of effects should never exceed FF_GAIN.
    > + */
    > +#define FF_MAX_EFFECTS FF_GAIN
    > +
    > #define FF_MAX 0x7f
    > #define FF_CNT (FF_MAX+1)
    >
    > --
    > 1.9.3
    >

    --
    Dmitry


    \
     
     \ /
      Last update: 2015-10-15 03:01    [W:7.261 / U:1.252 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site