Re: [patch 03/11] input: new force feedback interface

Anssi Hannula
2006-05-22T16:10:19Z

Andrew Morton wrote:
> Anssi Hannula <anssi.hannula@gmail.com> wrote:
>
>>Implement a new force feedback interface, in which all non-driver-specific
>>operations are separated to a common module. This module handles effect type
>>validations, effect timers, locking, etc.
>>
>>As a result, support is added for gain and envelope for memoryless devices,
>>periodic => rumble conversion for memoryless devices and rumble => periodic
>>conversion for devices with periodic support instead of rumble support. Also
>>the effect memory of devices is not emptied if the root user opens and closes
>>the device while another user is using effects. This module also obsoletes
>>some flawed locking and timer code in few ff drivers.
>>
>>The module is named ff-effects. If INPUT_FF_EFFECTS is enabled, the force
>>feedback drivers and interfaces (evdev) will be depending on it.
>>
>>Userspace interface is left unaltered.
>>
>
>
> Nice-looking patches.
>

Thanks for looking and providing helpful comments :)

>>+#define spin_ff_cond_lock(_ff, _flags) \
>>+ do { \
>>+ if (!_ff->driver->playback) \
>>+ spin_lock_irqsave(&_ff->atomiclock, _flags); \
>>+ } while (0);
>>+
>>+#define spin_ff_cond_unlock(_ff, _flags) \
>>+ do { \
>>+ if (!_ff->driver->playback) \
>>+ spin_unlock_irqrestore(&_ff->atomiclock, _flags); \
>>+ } while (0);
>
>
> Making these static inline functions would deuglify them a bit.
>

I put them like that because spin_lock_irqsave is a macro that uses the
local variable "flags".
But yes, I can probably pass that parameter to an inline function as a
pointer. I'll change that.

>>+static int input_ff_effect_access(struct input_dev *dev, int id, int override)
>>+{
>>+ struct ff_device *ff = dev->ff;
>>+ if (id < dev->ff_effects_max && id >= 0 && test_bit(FF_EFFECT_USED, ff->effects[id].flags))
>
>
> Kernel does have an 80-columns rule, but input seems to have always spurned it.
>
>
>>+static int input_ff_envelope_time(struct ff_effect_status *effect, struct ff_envelope *envelope, unsigned long *event_time)
>>+{
>>+ unsigned long fade_start;
>>+ if (!envelope)
>>+ return 0;
>>+
>>+ if (envelope->attack_length && time_after(effect->play_at + msecs_to_jiffies(envelope->attack_length), effect->adj_at)) {
>
>
> Try using an 80-column wondow for a while ;)

Okay, I'll make the lines shorter.

>
>
>>+ return value;
>>+ }
>>+
>>+ difference = abs(value) - envelope_level;
>>+
>>+ debug("difference = %d", difference);
>>+ debug("time_from_level = 0x%x", time_from_level);
>>+ debug("time_of_envelope = 0x%x", time_of_envelope);
>>+ if (difference < 0)
>>+ difference = -((-difference) * time_from_level / time_of_envelope);
>>+ else
>>+ difference = difference * time_from_level / time_of_envelope;
>
>
> You've checked there's no possibility of divide-by-zero here?
>

Yes, the "time_of_envelope" is set a few lines above from
"envelope->attack_length" or "envelope->fade_length", and there is an if
block that checks they're non-zero.

>>+
>>+static int input_ff_safe_sum(int a, int b, int limit) {
>
>
> The opening brace goes in column zero, please.
>
>
>>+ int c;
>>+ if (!a)
>>+ return b;
>>+ c = a + b;
>>+ if (c > limit)
>>+ return limit;
>>+ return c;
>>+}
>>+
>>+static s8 input_ff_s8_sum(int a, int b) {
>
>
> dittoes.

Okay, will fix.

>
>>+ int c;
>>+ c = input_ff_safe_sum(a, b, 0x7f);
>>+ if (c < -0x80)
>>+ return -0x80;
>>+ return c;
>>+}
>>
>>...
>>
>>+static void input_ff_timer(unsigned long timer_data)
>>+{
>>+ struct input_dev *dev = (struct input_dev *) timer_data;
>>+ struct ff_device *ff = dev->ff;
>>+ struct ff_effect effect;
>>+ int i;
>>+ unsigned long flags;
>>+ int effects_pending;
>>+ unsigned long effect_handled[NBITS(FF_EFFECTS_MAX)];
>
>
> DECLARE_BITMAP would be more usual. (Yes, it should have been called
> DEFINE_BITMAP).
>

Ok.

>>+ int effect_type;
>>+ int safety;
>>+
>>+ debug("timer: updating effects");
>>+
>>+ spin_lock_irqsave(&ff->atomiclock, flags);
>>+
>>+ memset(effect_handled, 0, sizeof(effect_handled));
>
>
> You could take the lock after the memset.
>

Ok.

>>+int input_ff_erase(struct input_dev *dev, int id)
>>+{
>>+ struct ff_device *ff;
>>+ unsigned long flags = 0;
>>+ int ret;
>>+ if (!test_bit(EV_FF, dev->evbit))
>>+ return -EINVAL;
>>+ mutex_lock(&dev->ff_lock);
>>+ ff = dev->ff;
>>+ if (!ff) {
>>+ mutex_unlock(&dev->ff_lock);
>>+ return -ENODEV;
>>+ }
>>+ spin_ff_cond_lock(ff, flags);
>>+ ret = _input_ff_erase(dev, id, current->pid == 0);
>>+ spin_ff_cond_unlock(ff, flags);
>>+
>>+ mutex_unlock(&dev->ff_lock);
>>+ return ret;
>>+}
>
>
> Perhaps you meant `current->uid == 0' here. There's no way in which pid
> 0 will call this code.

Right, a silly mistake.

> What's happening here anyway? Why does this code need to know about pids?
>
> Checking for uid==0 woud be a fishy thing to do as well.

User ID 0 is allowed to delete effects of other users. Pids are used to
keep a track of what process owns what effects. This is the same
behaviour as before.

There is a problem with this, though:
When a process closes any fd to this device, all pid-matching effects
are deleted whether the process has another fd using the device or not.

One solution would probably be to add some handle parameter to
input_ff_upload() and input_ff_erase(), and then in
evdev_ioctl_handler() pass an id unique to this fd. Then effects would
be fd-specific, not pid-specific. I think the uid == 0 thing can also be
dropped... I don't think the root user needs ability to override user
effects (it can delete them anyway, just kill the user process owning
the effects).

WDYT?

>
>>+static int input_ff_flush(struct input_dev *dev, struct file *file)
>>+{
>>+ struct ff_device *ff;
>>+ unsigned long flags = 0;
>>+ int i;
>>+ debug("flushing now");
>>+ mutex_lock(&dev->ff_lock);
>>+ ff = dev->ff;
>>+ if (!ff) {
>>+ mutex_unlock(&dev->ff_lock);
>>+ return -ENODEV;
>>+ }
>>+ spin_ff_cond_lock(ff, flags);
>>+ for (i = 0; i < dev->ff_effects_max; i++) {
>>+ _input_ff_erase(dev, i, 0);
>>+ }
>
>
> Unneeded braces.
>

Will remove.

>>+ spin_ff_cond_unlock(ff, flags);
>>+ mutex_unlock(&dev->ff_lock);
>>+ return 0;
>>+}
>>+
>>+
>>+ ff->effects[id].flags[0] = 0;
>>+ ff->effects[id].effect = *effect;
>>+
>>+ if (ff->driver->playback) {
>>+ if (!test_bit(effect->type, ff->flags))
>>+ input_ff_convert_effect(dev, effect);
>>+ ret = ff->driver->upload(dev, effect, NULL);
>>+ if (!ret)
>>+ set_bit(FF_EFFECT_USED, ff->effects[id].flags);
>>+ mutex_unlock(&dev->ff_lock);
>>+ return ret;
>>+ }
>>+ set_bit(FF_EFFECT_USED, ff->effects[id].flags);
>>+
>>+ } else {
>>+ id = effect->id;
>>+
>>+ ret = input_ff_effect_access(dev, id, 1);
>>+ if (ret) {
>>+ spin_ff_cond_unlock(ff, flags);
>>+ mutex_unlock(&dev->ff_lock);
>>+ return ret;
>>+ }
>>+
>>+ if (effect->type != ff->effects[id].effect.type ||
>>+ (effect->type == FF_PERIODIC && effect->u.periodic.waveform !=
>>+ ff->effects[id].effect.u.periodic.waveform)) {
>>+ spin_ff_cond_unlock(ff, flags);
>>+ mutex_unlock(&dev->ff_lock);
>>+ return -EINVAL;
>>+ }
>>+
>>+ if (ff->driver->playback) {
>>+ if (!test_bit(effect->type, ff->flags))
>>+ input_ff_convert_effect(dev, effect);
>>+ ret = ff->driver->upload(dev, effect, &ff->effects[id].effect);
>>+ ff->effects[id].effect = *effect;
>>+ mutex_unlock(&dev->ff_lock);
>>+ return ret;
>
>
> I think we're missing a spin_ff_cond_unlock() here?

Well, spin_ff_cond_unlock() checks for ff->driver->playback and it is
already tested in the if block above.

>
>>+ }
>>+ ff->effects[id].effect = *effect;
>>+ clear_bit(FF_EFFECT_PLAYING, ff->effects[id].flags);
>>+
>>+ }
>>+
>>+ spin_unlock_irqrestore(&ff->atomiclock, flags);
>>+ mutex_unlock(&dev->ff_lock);
>>+ return ret;
>>+}
>
>
> And here we have spin_unlock_irqrestore() instead of spin_ff_cond_unlock().

If there is no need to unlock, one of the above "if
(ff->driver->playback)" would be true and the function would've already
returned before this point.

> It would be best to convert this function to have a single return point.
> That tends to prevent problems like this from happening, and from creeping
> in later on.

I agree that the locking is too confusing in input_ff_event() and
input_ff_upload(), even if it is correct.

I'll modify the function to have a single return point, or maybe split
the function for the two different locking paths, which then call common
functions without the need to cond_lock. I guess that could be done for
all cond_locking functions.

>
>>+int input_ff_allocate(struct input_dev *dev)
>>+{
>>+ debug("allocating device");
>>+ mutex_lock(&dev->ff_lock);
>>+ if (dev->ff)
>>+ printk(KERN_ERR "ff-effects: allocating to non-NULL pointer\n");
>>+ dev->ff = kzalloc(sizeof(*dev->ff), GFP_KERNEL);
>>+ if (!dev->ff) {
>>+ mutex_unlock(&dev->ff_lock);
>>+ return -ENOMEM;
>>+ }
>>+ spin_lock_init(&dev->ff->atomiclock);
>>+ init_timer(&dev->ff->timer);
>>+ dev->ff->timer.function = input_ff_timer;
>>+ dev->ff->timer.data = (unsigned long) dev;
>>+ dev->ff->event = input_ff_event;
>
>
> setup_timer()
>

Will change.

>>+ mutex_unlock(&dev->ff_lock);
>>+ debug("ff allocated");
>>+ return 0;
>>+}
>>+
>>
>>...
>>
>>Index: linux-2.6.17-rc4-git1/drivers/input/Kconfig
>>===================================================================
>>--- linux-2.6.17-rc4-git1.orig/drivers/input/Kconfig 2006-03-20 07:53:29.000000000 +0200
>>+++ linux-2.6.17-rc4-git1/drivers/input/Kconfig 2006-05-14 02:28:42.000000000 +0300
>>@@ -24,6 +24,14 @@ config INPUT
>>
>> if INPUT
>>
>>+config INPUT_FF_EFFECTS
>>+ tristate "Force feedback effects"
>>+ help
>>+ Say Y here if you want to be able to play force feedback effects.
>>+
>>+ To compile this driver as a module, choose M here: the
>>+ module will be called ff-effects.
>
>
> hm. I'd have expected more dependencies than this.
>

Only INPUT.

>> comment "Userland interfaces"
>>
>> config INPUT_MOUSEDEV
>>@@ -110,6 +118,7 @@ config INPUT_TSDEV_SCREEN_Y
>>
>> config INPUT_EVDEV
>> tristate "Event interface"
>>+ depends on INPUT_FF_EFFECTS || INPUT_FF_EFFECTS=n
>
>
> Isn't that always true?
>

This disallows building evdev as builtin and ff-effects as module.

>>+
>>+struct ff_effect_status {
>>+ pid_t owner;
>
>
> This code is almost devoid of comments. Those which it does have tend to
> cover little low-level implementation details. But it's the *big* things
> which a reader is not able to learn from the implementation, and which
> should be commented. Like: why on earth does this code need to know about
> pids?

Okay, I'll try to add some.

>
>>+#if defined(CONFIG_INPUT_FF_EFFECTS_MODULE) || defined(CONFIG_INPUT_FF_EFFECTS)
>
>
> No, we shouldn't use CONFIG_FOO_MODULE. We just don't know at compile-time
> whether the user will later compile and insert a particular module.
>

Right... so maybe we should just make ff-effects a bool instead of
tristate or put it in the input module?

>>+ mutex_lock(&dev->ff_lock);
>>+ del_timer_sync(&ff->timer);
>>+ dev->flush = NULL;
>>+ dev->ff = NULL;
>>+ kfree(ff);
>>+ mutex_unlock(&dev->ff_lock);
>
>
> The kfree can be moved outside the lock.
>

Indeed.

BTW, what is the best way to send corrected patches for this patchset?
Probably as a reply to the individual patches?