From 63e0f3b39c4c36fa94d5d2ab3942f7984a115bc3 Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba@suse.com>
Date: Mon, 30 May 2022 15:47:06 +0200
Subject: [PATCH] btrfs-progs: kernel-lib: make headers C++ compatible

The snapper build fails due to updates to kernel-lib files, the type
casts do not work the same way in C++. Simplify READ_ONCE/WRITE_ONCE
even more, drop use of 'new' as identifier.

Issue: https://github.com/openSUSE/snapper/issues/725
Signed-off-by: David Sterba <dsterba@suse.com>
---
 kerncompat.h      | 21 +++------------------
 kernel-lib/list.h | 24 ++++++++++++++++--------
 2 files changed, 19 insertions(+), 26 deletions(-)

diff --git a/kerncompat.h b/kerncompat.h
index 64c2c0c3..f6477990 100644
--- a/kerncompat.h
+++ b/kerncompat.h
@@ -538,29 +538,14 @@ struct __una_u64 { __le64 x; } __attribute__((__packed__));
  * Changed:
  * - __unqual_scalar_typeof: volatile cast to typeof()
  * - compiletime_assert_rwonce_type: no word size compatibility checks
+ * - no const volatile cast
  */
 
-/*
- * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
- * atomicity. Note that this may result in tears!
- */
-#ifndef __READ_ONCE
-#define __READ_ONCE(x)	(*(const volatile typeof(x) *)&(x))
-#endif
-
-#define READ_ONCE(x)							\
-({									\
-	__READ_ONCE(x);							\
-})
-
-#define __WRITE_ONCE(x, val)						\
-do {									\
-	*(volatile typeof(x) *)&(x) = (val);				\
-} while (0)
+#define READ_ONCE(x)		(x)
 
 #define WRITE_ONCE(x, val)						\
 do {									\
-	__WRITE_ONCE(x, val);						\
+	(x) = (val);							\
 } while (0)
 
 #endif
diff --git a/kernel-lib/list.h b/kernel-lib/list.h
index 11adb03a..0fe78971 100644
--- a/kernel-lib/list.h
+++ b/kernel-lib/list.h
@@ -28,6 +28,10 @@
 #include <stddef.h>
 #include <stdbool.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define LIST_POISON1  ((void *) 0x00100100)
 #define LIST_POISON2  ((void *) 0x00200200)
 
@@ -187,8 +191,8 @@ static inline void __list_del_entry(struct list_head *entry)
 static inline void list_del(struct list_head *entry)
 {
 	__list_del_entry(entry);
-	entry->next = LIST_POISON1;
-	entry->prev = LIST_POISON2;
+	entry->next = (struct list_head *)LIST_POISON1;
+	entry->prev = (struct list_head *)LIST_POISON2;
 }
 
 /**
@@ -901,8 +905,8 @@ static inline void __hlist_del(struct hlist_node *n)
 static inline void hlist_del(struct hlist_node *n)
 {
 	__hlist_del(n);
-	n->next = LIST_POISON1;
-	n->pprev = LIST_POISON2;
+	n->next = (struct hlist_node *)LIST_POISON1;
+	n->pprev = (struct hlist_node **)LIST_POISON2;
 }
 
 /**
@@ -1012,11 +1016,11 @@ hlist_is_singular_node(struct hlist_node *n, struct hlist_head *h)
  * reference of the first entry if it exists.
  */
 static inline void hlist_move_list(struct hlist_head *old,
-				   struct hlist_head *new)
+				   struct hlist_head *xnew)
 {
-	new->first = old->first;
-	if (new->first)
-		new->first->pprev = &new->first;
+	xnew->first = old->first;
+	if (xnew->first)
+		xnew->first->pprev = &xnew->first;
 	old->first = NULL;
 }
 
@@ -1076,4 +1080,8 @@ static inline void hlist_move_list(struct hlist_head *old,
 	     pos && ({ n = pos->member.next; 1; });			\
 	     pos = hlist_entry_safe(n, typeof(*pos), member))
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif