Re: [PATCH v2 3/6] staging:iio:events: Use kfifo for event queue

[Jonathan Cameron <jic23@kernel.org>]

On 12/19/2011 10:29 AM, Lars-Peter Clausen wrote:
> The current IIO event code uses a list to emulate FIFO like behaviour.
> Just use a kfifo directly instead to implement the event queue. As part of this
> patch the maximum of events in the queue is increased from 10 to 16 since kfifo
> requires a power of two for the number of fifo elements.
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
> ---
>  drivers/staging/iio/industrialio-event.c |   88 +++++++-----------------------
>  1 files changed, 21 insertions(+), 67 deletions(-)
> 
> diff --git a/drivers/staging/iio/industrialio-event.c b/drivers/staging/iio/industrialio-event.c
> index a7b345d..d63aa0b 100644
> --- a/drivers/staging/iio/industrialio-event.c
> +++ b/drivers/staging/iio/industrialio-event.c
> @@ -13,6 +13,7 @@
>  #include <linux/device.h>
>  #include <linux/fs.h>
>  #include <linux/kernel.h>
> +#include <linux/kfifo.h>
>  #include <linux/module.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> @@ -24,22 +25,10 @@
>  #include "events.h"
>  
>  /**
> - * struct iio_detected_event_list - list element for events that have occurred
> - * @list:		linked list header
> - * @ev:			the event itself
> - */
> -struct iio_detected_event_list {
> -	struct list_head		list;
> -	struct iio_event_data		ev;
> -};
> -
> -/**
>   * struct iio_event_interface - chrdev interface for an event line
>   * @wait:		wait queue to allow blocking reads of events
>   * @event_list_lock:	mutex to protect the list of detected events
>   * @det_events:		list of detected events
> - * @max_events:		maximum number of events before new ones are dropped
> - * @current_events:	number of events in detected list
>   * @dev_attr_list:	list of event interface sysfs attribute
>   * @flags:		file operations related flags including busy flag.
>   * @group:		event interface sysfs attribute group
> @@ -47,9 +36,8 @@ struct iio_detected_event_list {
>  struct iio_event_interface {
>  	wait_queue_head_t	wait;
>  	struct mutex		event_list_lock;
> -	struct list_head	det_events;
> -	int			max_events;
> -	int			current_events;
> +	DECLARE_KFIFO(det_events, struct iio_event_data, 16);
> +
>  	struct list_head	dev_attr_list;
>  	unsigned long		flags;
>  	struct attribute_group	group;
> @@ -58,34 +46,25 @@ struct iio_event_interface {
>  int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp)
>  {
>  	struct iio_event_interface *ev_int = indio_dev->event_interface;
> -	struct iio_detected_event_list *ev;
> -	int ret = 0;
> +	struct iio_event_data ev;
> +	int copied;
>  
>  	/* Does anyone care? */
>  	mutex_lock(&ev_int->event_list_lock);
>  	if (test_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
> -		if (ev_int->current_events == ev_int->max_events) {
> -			mutex_unlock(&ev_int->event_list_lock);
> -			return 0;
> -		}
> -		ev = kmalloc(sizeof(*ev), GFP_KERNEL);
> -		if (ev == NULL) {
> -			ret = -ENOMEM;
> -			mutex_unlock(&ev_int->event_list_lock);
> -			goto error_ret;
> -		}
> -		ev->ev.id = ev_code;
> -		ev->ev.timestamp = timestamp;
>  
> -		list_add_tail(&ev->list, &ev_int->det_events);
> -		ev_int->current_events++;
> +		ev.id = ev_code;
> +		ev.timestamp = timestamp;
> +
> +		copied = kfifo_put(&ev_int->det_events, &ev);
> +
>  		mutex_unlock(&ev_int->event_list_lock);
> -		wake_up_interruptible(&ev_int->wait);
> +		if (copied != 0)
> +			wake_up_interruptible(&ev_int->wait);
>  	} else
>  		mutex_unlock(&ev_int->event_list_lock);
>  
> -error_ret:
> -	return ret;
> +	return 0;
>  }
>  EXPORT_SYMBOL(iio_push_event);
>  
> @@ -95,15 +74,14 @@ static ssize_t iio_event_chrdev_read(struct file *filep,
>  				     loff_t *f_ps)
>  {
>  	struct iio_event_interface *ev_int = filep->private_data;
> -	struct iio_detected_event_list *el;
> -	size_t len = sizeof(el->ev);
> +	unsigned int copied;
>  	int ret;
>  
> -	if (count < len)
> +	if (count < sizeof(struct iio_event_data))
>  		return -EINVAL;
>  
>  	mutex_lock(&ev_int->event_list_lock);
> -	if (list_empty(&ev_int->det_events)) {
> +	if (kfifo_is_empty(&ev_int->det_events)) {
>  		if (filep->f_flags & O_NONBLOCK) {
>  			ret = -EAGAIN;
>  			goto error_mutex_unlock;
> @@ -111,39 +89,25 @@ static ssize_t iio_event_chrdev_read(struct file *filep,
>  		mutex_unlock(&ev_int->event_list_lock);
>  		/* Blocking on device; waiting for something to be there */
>  		ret = wait_event_interruptible(ev_int->wait,
> -					       !list_empty(&ev_int
> -							   ->det_events));
> +					!kfifo_is_empty(&ev_int->det_events));
>  		if (ret)
>  			goto error_ret;
>  		/* Single access device so no one else can get the data */
>  		mutex_lock(&ev_int->event_list_lock);
>  	}
>  
> -	el = list_first_entry(&ev_int->det_events,
> -			      struct iio_detected_event_list,
> -			      list);
> -	if (copy_to_user(buf, &(el->ev), len)) {
> -		ret = -EFAULT;
> -		goto error_mutex_unlock;
> -	}
> -	list_del(&el->list);
> -	ev_int->current_events--;
>  	mutex_unlock(&ev_int->event_list_lock);
> -	kfree(el);
> -
> -	return len;
> +	ret = kfifo_to_user(&ev_int->det_events, buf, count, &copied);
>  
>  error_mutex_unlock:
>  	mutex_unlock(&ev_int->event_list_lock);
>  error_ret:
> -
> -	return ret;
> +	return ret ? ret : copied;
>  }
>  
>  static int iio_event_chrdev_release(struct inode *inode, struct file *filep)
>  {
>  	struct iio_event_interface *ev_int = filep->private_data;
> -	struct iio_detected_event_list *el, *t;
>  
>  	mutex_lock(&ev_int->event_list_lock);
>  	clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
> @@ -152,11 +116,7 @@ static int iio_event_chrdev_release(struct inode *inode, struct file *filep)
>  	 * clear out any awaiting events. The mask will prevent
>  	 * any new __iio_push_event calls running.
>  	 */
> -	list_for_each_entry_safe(el, t, &ev_int->det_events, list) {
> -		list_del(&el->list);
> -		kfree(el);
> -	}
> -	ev_int->current_events = 0;
> +	kfifo_reset_out(&ev_int->det_events);
>  	mutex_unlock(&ev_int->event_list_lock);
>  
>  	return 0;
> @@ -268,9 +228,6 @@ static ssize_t iio_ev_value_store(struct device *dev,
>  	unsigned long val;
>  	int ret;
>  
> -	if (!indio_dev->info->write_event_value)
> -		return -EINVAL;
> -
>  	ret = strict_strtoul(buf, 10, &val);
>  	if (ret)
>  		return ret;
> @@ -401,10 +358,7 @@ static bool iio_check_for_dynamic_events(struct iio_dev *indio_dev)
>  static void iio_setup_ev_int(struct iio_event_interface *ev_int)
>  {
>  	mutex_init(&ev_int->event_list_lock);
> -	/* discussion point - make this variable? */
> -	ev_int->max_events = 10;
> -	ev_int->current_events = 0;
> -	INIT_LIST_HEAD(&ev_int->det_events);
> +	INIT_KFIFO(ev_int->det_events);
>  	init_waitqueue_head(&ev_int->wait);
>  }
>