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klist: implement klist_prev()

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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>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
This commit is contained in:
Andy Shevchenko 2015-07-27 18:03:59 +03:00 committed by Lee Jones
parent ddef08dd00
commit 2e0fed7f7c
2 changed files with 42 additions and 0 deletions
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1
include/linux/klist.h
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@ -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

41
lib/klist.c
View File

@ -323,6 +323,47 @@ static struct klist_node *to_klist_node(struct list_head *n)
return container_of(n, struct klist_node, n_node);
}
/**
* 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.