From: Felix Fietkau <nbd@nbd.name>
Date: Fri, 29 Apr 2022 10:57:25 +0000 (+0200)
Subject: list.h: add container_of_safe macro
X-Git-Url: http://git.openwrt.org/?a=commitdiff_plain;h=45210ce14136d9410d7139fba816c4465b4c7af5;p=project%2Flibubox.git

list.h: add container_of_safe macro

It works like container_of, except that it also deals with NULL pointers

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

diff --git a/list.h b/list.h
index a2cb241..6aa7b2a 100644
--- a/list.h
+++ b/list.h
@@ -42,6 +42,14 @@
 	})
 #endif
 
+#ifndef container_of_safe
+#define container_of_safe(ptr, type, member)						\
+	({										\
+		const __typeof__(((type *) NULL)->member) *__mptr = (ptr);		\
+		__mptr ? (type *)((char *) __mptr - offsetof(type, member)) : NULL;	\
+	})
+#endif
+
 struct list_head {
 	struct list_head *next;
 	struct list_head *prev;