Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751040AbbEYQJn (ORCPT ); Mon, 25 May 2015 12:09:43 -0400 Received: from mga09.intel.com ([134.134.136.24]:35279 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800AbbEYQJj (ORCPT ); Mon, 25 May 2015 12:09:39 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,492,1427785200"; d="scan'208";a="731397833" From: Andy Shevchenko To: "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org, Greg Kroah-Hartman , Vinod Koul , Lee Jones , Andrew Morton , Mika Westerberg , linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, Heikki Krogerus , Jarkko Nikula Cc: Andy Shevchenko Subject: [PATCH v2 4/8] klist: implement klist_prev() Date: Mon, 25 May 2015 19:09:28 +0300 Message-Id: <1432570172-86963-5-git-send-email-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1432570172-86963-1-git-send-email-andriy.shevchenko@linux.intel.com> References: <1432570172-86963-1-git-send-email-andriy.shevchenko@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2450 Lines: 82 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 --- include/linux/klist.h | 1 + lib/klist.c | 41 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 42 insertions(+) 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. * -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/