Messages in this thread | | | Date | Thu, 25 May 2006 12:00:54 +0300 | From | Anssi Hannula <> | Subject | Re: [patch 03/11] input: new force feedback interface |
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Here's this reply again with different From email address, so that Andrew Morton gets it too:
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?
-- Anssi Hannula
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