6 files changed, 266 insertions, 0 deletions
diff --git a/lib/ccan/container_of/_info b/lib/ccan/container_of/_info
new file mode 100644
index 0000000000..2f45ca7ccd
--- /dev/null
+++ b/lib/ccan/container_of/_info
@@ -0,0 +1,63 @@
+#include <stdio.h>
+#include <string.h>
+#include "config.h"
+
+/**
+ * container_of - routine for upcasting
+ *
+ * It is often convenient to create code where the caller registers a pointer
+ * to a generic structure and a callback.  The callback might know that the
+ * pointer points to within a larger structure, and container_of gives a
+ * convenient and fairly type-safe way of returning to the enclosing structure.
+ *
+ * This idiom is an alternative to providing a void * pointer for every
+ * callback.
+ *
+ * Example:
+ *	#include <stdio.h>
+ *	#include <ccan/container_of/container_of.h>
+ *
+ *	struct timer {
+ *		void *members;
+ *	};
+ *
+ *	struct info {
+ *		int my_stuff;
+ *		struct timer timer;
+ *	};
+ *
+ *	static void register_timer(struct timer *timer)
+ *	{
+ *		//...
+ *	}
+ *
+ *	static void my_timer_callback(struct timer *timer)
+ *	{
+ *		struct info *info = container_of(timer, struct info, timer);
+ *		printf("my_stuff is %u\n", info->my_stuff);
+ *	}
+ *
+ *	int main(void)
+ *	{
+ *		struct info info = { .my_stuff = 1 };
+ *
+ *		register_timer(&info.timer);
+ *		// ...
+ *		return 0;
+ *	}
+ *
+ * License: Public domain
+ * Author: Rusty Russell <rusty@rustcorp.com.au>
+ */
+int main(int argc, char *argv[])
+{
+	if (argc != 2)
+		return 1;
+
+	if (strcmp(argv[1], "depends") == 0) {
+		printf("ccan/check_type\n");
+		return 0;
+	}
+
+	return 1;
+}
diff --git a/lib/ccan/container_of/container_of.h b/lib/ccan/container_of/container_of.h
new file mode 100644
index 0000000000..1c9d147ae0
--- /dev/null
+++ b/lib/ccan/container_of/container_of.h
@@ -0,0 +1,108 @@
+#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 */
diff --git a/lib/ccan/container_of/test/compile_fail-bad-type.c b/lib/ccan/container_of/test/compile_fail-bad-type.c
new file mode 100644
index 0000000000..b7a1459386
--- /dev/null
+++ b/lib/ccan/container_of/test/compile_fail-bad-type.c
@@ -0,0 +1,22 @@
+#include <ccan/container_of/container_of.h>
+#include <stdlib.h>
+
+struct foo {
+	int a;
+	char b;
+};
+
+int main(int argc, char *argv[])
+{
+	struct foo foo = { .a = 1, .b = 2 };
+	int *intp = &foo.a;
+	char *p;
+
+#ifdef FAIL
+	/* p is a char *, but this gives a struct foo * */
+	p = container_of(intp, struct foo, a);
+#else
+	p = (char *)intp;
+#endif
+	return p == NULL;
+}
diff --git a/lib/ccan/container_of/test/compile_fail-types.c b/lib/ccan/container_of/test/compile_fail-types.c
new file mode 100644
index 0000000000..cae1c7abd2
--- /dev/null
+++ b/lib/ccan/container_of/test/compile_fail-types.c
@@ -0,0 +1,22 @@
+#include <ccan/container_of/container_of.h>
+#include <stdlib.h>
+
+struct foo {
+	int a;
+	char b;
+};
+
+int main(int argc, char *argv[])
+{
+	struct foo foo = { .a = 1, .b = 2 }, *foop;
+	int *intp = &foo.a;
+
+#ifdef FAIL
+	/* b is a char, but intp is an int * */
+	foop = container_of(intp, struct foo, b);
+#else
+	foop = NULL;
+#endif
+	(void) foop; /* Suppress unused-but-set-variable warning. */
+	return intp == NULL;
+}
diff --git a/lib/ccan/container_of/test/compile_fail-var-types.c b/lib/ccan/container_of/test/compile_fail-var-types.c
new file mode 100644
index 0000000000..f254d92102
--- /dev/null
+++ b/lib/ccan/container_of/test/compile_fail-var-types.c
@@ -0,0 +1,25 @@
+#include <ccan/container_of/container_of.h>
+#include <stdlib.h>
+
+struct foo {
+	int a;
+	char b;
+};
+
+int main(int argc, char *argv[])
+{
+	struct foo foo = { .a = 1, .b = 2 }, *foop;
+	int *intp = &foo.a;
+
+#ifdef FAIL
+	/* b is a char, but intp is an int * */
+	foop = container_of_var(intp, foop, b);
+#if !HAVE_TYPEOF
+#error "Unfortunately we don't fail if we don't have typeof."
+#endif
+#else
+	foop = NULL;
+#endif
+	(void) foop; /* Suppress unused-but-set-variable warning. */
+	return intp == NULL;
+}
diff --git a/lib/ccan/container_of/test/run.c b/lib/ccan/container_of/test/run.c
new file mode 100644
index 0000000000..5da440a1e5
--- /dev/null
+++ b/lib/ccan/container_of/test/run.c
@@ -0,0 +1,26 @@
+#include <ccan/container_of/container_of.h>
+#include <ccan/tap/tap.h>
+
+struct foo {
+	int a;
+	char b;
+};
+
+int main(int argc, char *argv[])
+{
+	struct foo foo = { .a = 1, .b = 2 };
+	int *intp = &foo.a;
+	char *charp = &foo.b;
+
+	plan_tests(8);
+	ok1(container_of(intp, struct foo, a) == &foo);
+	ok1(container_of(charp, struct foo, b) == &foo);
+	ok1(container_of_var(intp, &foo, a) == &foo);
+	ok1(container_of_var(charp, &foo, b) == &foo);
+
+	ok1(container_off(struct foo, a) == 0);
+	ok1(container_off(struct foo, b) == offsetof(struct foo, b));
+	ok1(container_off_var(&foo, a) == 0);
+	ok1(container_off_var(&foo, b) == offsetof(struct foo, b));
+	return exit_status();
+}