1 files changed, 109 insertions, 0 deletions
diff --git a/ccan/container_of/container_of.h b/ccan/container_of/container_of.h
new file mode 100644
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+++ b/ccan/container_of/container_of.h
@@ -0,0 +1,109 @@
+/* CC0 (Public domain) - see LICENSE file for details */
+#ifndef CCAN_CONTAINER_OF_H
+#define CCAN_CONTAINER_OF_H
+#include <stddef.h>
+
+#include "config.h"
+#include <ccan/check_type/check_type.h>
+
+/**
+ * container_of - get pointer to enclosing structure
+ * @member_ptr: pointer to the structure member
+ * @containing_type: the type this member is within
+ * @member: the name of this member within the structure.
+ *
+ * Given a pointer to a member of a structure, this macro does pointer
+ * subtraction to return the pointer to the enclosing type.
+ *
+ * Example:
+ *        struct foo {
+ *                int fielda, fieldb;
+ *                // ...
+ *        };
+ *        struct info {
+ *                int some_other_field;
+ *                struct foo my_foo;
+ *        };
+ *
+ *        static struct info *foo_to_info(struct foo *foo)
+ *        {
+ *                return container_of(foo, struct info, my_foo);
+ *        }
+ */
+#define container_of(member_ptr, containing_type, member)                \
+         ((containing_type *)                                                \
+          ((char *)(member_ptr)                                                \
+           - container_off(containing_type, member))                        \
+          + check_types_match(*(member_ptr), ((containing_type *)0)->member))
+
+/**
+ * container_off - get offset to enclosing structure
+ * @containing_type: the type this member is within
+ * @member: the name of this member within the structure.
+ *
+ * Given a pointer to a member of a structure, this macro does
+ * typechecking and figures out the offset to the enclosing type.
+ *
+ * Example:
+ *        struct foo {
+ *                int fielda, fieldb;
+ *                // ...
+ *        };
+ *        struct info {
+ *                int some_other_field;
+ *                struct foo my_foo;
+ *        };
+ *
+ *        static struct info *foo_to_info(struct foo *foo)
+ *        {
+ *                size_t off = container_off(struct info, my_foo);
+ *                return (void *)((char *)foo - off);
+ *        }
+ */
+#define container_off(containing_type, member)        \
+        offsetof(containing_type, member)
+
+/**
+ * container_of_var - get pointer to enclosing structure using a variable
+ * @member_ptr: pointer to the structure member
+ * @container_var: a pointer of same type as this member's container
+ * @member: the name of this member within the structure.
+ *
+ * Given a pointer to a member of a structure, this macro does pointer
+ * subtraction to return the pointer to the enclosing type.
+ *
+ * Example:
+ *        static struct info *foo_to_i(struct foo *foo)
+ *        {
+ *                struct info *i = container_of_var(foo, i, my_foo);
+ *                return i;
+ *        }
+ */
+#if HAVE_TYPEOF
+#define container_of_var(member_ptr, container_var, member) \
+        container_of(member_ptr, typeof(*container_var), member)
+#else
+#define container_of_var(member_ptr, container_var, member)        \
+        ((void *)((char *)(member_ptr)        -                        \
+                  container_off_var(container_var, member)))
+#endif
+
+/**
+ * container_off_var - get offset of a field in enclosing structure
+ * @container_var: a pointer to a container structure
+ * @member: the name of a member within the structure.
+ *
+ * Given (any) pointer to a structure and a its member name, this
+ * macro does pointer subtraction to return offset of member in a
+ * structure memory layout.
+ *
+ */
+#if HAVE_TYPEOF
+#define container_off_var(var, member)                \
+        container_off(typeof(*var), member)
+#else
+#define container_off_var(var, member)                        \
+        ((char *)&(var)->member - (char *)(var))
+#endif
+
+#endif /* CCAN_CONTAINER_OF_H */