linux-kernel - [PATCH 1/9] list: add list_last_entry_or

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Message-Id: <20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-v1-1-48920b9cf369@bootlin.com>
Date: Wed, 09 Jul 2025 18:48:00 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Liu Ying <victor.liu@....com>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
 Philipp Zabel <p.zabel@...gutronix.de>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>, 
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 Zijun Hu <quic_zijuhu@...cinc.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 1/9] list: add list_last_entry_or_null()

Add an equivalent of list_first_entry_or_null() to obtain the last element
of a list.

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

---

Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Zijun Hu <quic_zijuhu@...cinc.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/list.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index e7e28afd28f8eef94ab6baec77e69ea104ba0391..7f7657e416209a2941b3f292b1334e9e0f2a3ca5 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -636,6 +636,20 @@ static inline void list_splice_tail_init(struct list_head *list,
 	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
 })
 
+/**
+ * list_last_entry_or_null - get the last element from a list
+ * @ptr:	the list head to take the element from.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Note that if the list is empty, it returns NULL.
+ */
+#define list_last_entry_or_null(ptr, type, member) ({ \
+	struct list_head *head__ = (ptr); \
+	struct list_head *pos__ = READ_ONCE(head__->prev); \
+	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
+
 /**
  * list_next_entry - get the next element in list
  * @pos:	the type * to cursor

-- 
2.50.0