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List:       dmaengine
Subject:    Re: [PATCH v6 4/8] klist: implement klist_prev()
From:       Lee Jones <lee.jones () linaro ! org>
Date:       2015-07-28 7:47:55
Message-ID: 20150728074755.GR21114 () x1
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On Mon, 27 Jul 2015, Andy Shevchenko wrote:

> klist_prev() gets the previous element in the list. It is useful to traverse
> through the list in reverse order, for example, to provide LIFO (last in first
> out) variant of access.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  include/linux/klist.h |  1 +
>  lib/klist.c           | 41 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)

Applied, thanks.  Pull request to follow.

> diff --git a/include/linux/klist.h b/include/linux/klist.h
> index 61e5b72..953f283 100644
> --- a/include/linux/klist.h
> +++ b/include/linux/klist.h
> @@ -63,6 +63,7 @@ extern void klist_iter_init(struct klist *k, struct klist_iter *i);
>  extern void klist_iter_init_node(struct klist *k, struct klist_iter *i,
>  				 struct klist_node *n);
>  extern void klist_iter_exit(struct klist_iter *i);
> +extern struct klist_node *klist_prev(struct klist_iter *i);
>  extern struct klist_node *klist_next(struct klist_iter *i);
>  
>  #endif
> diff --git a/lib/klist.c b/lib/klist.c
> index 89b485a..d74cf7a 100644
> --- a/lib/klist.c
> +++ b/lib/klist.c
> @@ -324,6 +324,47 @@ static struct klist_node *to_klist_node(struct list_head *n)
>  }
>  
>  /**
> + * klist_prev - Ante up prev node in list.
> + * @i: Iterator structure.
> + *
> + * First grab list lock. Decrement the reference count of the previous
> + * node, if there was one. Grab the prev node, increment its reference
> + * count, drop the lock, and return that prev node.
> + */
> +struct klist_node *klist_prev(struct klist_iter *i)
> +{
> +	void (*put)(struct klist_node *) = i->i_klist->put;
> +	struct klist_node *last = i->i_cur;
> +	struct klist_node *prev;
> +
> +	spin_lock(&i->i_klist->k_lock);
> +
> +	if (last) {
> +		prev = to_klist_node(last->n_node.prev);
> +		if (!klist_dec_and_del(last))
> +			put = NULL;
> +	} else
> +		prev = to_klist_node(i->i_klist->k_list.prev);
> +
> +	i->i_cur = NULL;
> +	while (prev != to_klist_node(&i->i_klist->k_list)) {
> +		if (likely(!knode_dead(prev))) {
> +			kref_get(&prev->n_ref);
> +			i->i_cur = prev;
> +			break;
> +		}
> +		prev = to_klist_node(prev->n_node.prev);
> +	}
> +
> +	spin_unlock(&i->i_klist->k_lock);
> +
> +	if (put && last)
> +		put(last);
> +	return i->i_cur;
> +}
> +EXPORT_SYMBOL_GPL(klist_prev);
> +
> +/**
>   * klist_next - Ante up next node in list.
>   * @i: Iterator structure.
>   *

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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