diff mbox

[v2,4/8] klist: implement klist_prev()

Message ID 1432570172-86963-5-git-send-email-andriy.shevchenko@linux.intel.com (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Andy Shevchenko May 25, 2015, 4:09 p.m. UTC 
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>
---
 include/linux/klist.h |  1 +
 lib/klist.c           | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

Comments

Greg KH June 1, 2015, 1:21 a.m. UTC | #1 
On Mon, May 25, 2015 at 07:09:28PM +0300, 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-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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diff mbox

Patch

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.
  *