container_of: use offsetof from stddef

Use standardized offsetof() macro from stddef.
Helps to build valid code with latest gcc10 with -O2.

2 files changed, 5 insertions, 10 deletions

diff --git a/base/memory/container_of.h b/base/memory/container_of.h
index 4e4c662bf..ddb795935 100644
--- a/base/memory/container_of.h
+++ b/base/memory/container_of.h
@@ -1,4 +1,4 @@
-// Copyright (C) 2018 Red Hat, Inc. All rights reserved.
+// Copyright (C) 2018 - 2020 Red Hat, Inc. All rights reserved.
 // 
 // This file is part of LVM2.
 //
@@ -13,10 +13,12 @@
 #ifndef BASE_MEMORY_CONTAINER_OF_H
 #define BASE_MEMORY_CONTAINER_OF_H
 
+#include <stddef.h>  // offsetof
+
 //----------------------------------------------------------------
 
 #define container_of(v, t, head) \
-    ((t *)((const char *)(v) - (const char *)&((t *) 0)->head))
+    ((t *)((const char *)(v) - offsetof(t, head)))
 
 //----------------------------------------------------------------
 
diff --git a/lib/device/bcache.h b/lib/device/bcache.h
index 4ef044c74..2950afa69 100644
--- a/lib/device/bcache.h
+++ b/lib/device/bcache.h
@@ -16,19 +16,12 @@
 #define BCACHE_H
 
 #include "device_mapper/all.h"
+#include "base/memory/container_of.h"
 
 #include <linux/fs.h>
 #include <stdint.h>
 #include <stdbool.h>
 
-/*----------------------------------------------------------------*/
-
-// FIXME: move somewhere more sensible
-#define container_of(v, t, head) \
-    ((t *)((const char *)(v) - (const char *)&((t *) 0)->head))
-
-/*----------------------------------------------------------------*/
-
 enum dir {
 	DIR_READ,
 	DIR_WRITE