Mailing List Archive

Provide a convenient and type-safe wrapper which does the correct
dance to subtract offsetof. This is very similar to the
"container_of" macro in the Linux kernel, but it has an additional
feature that instead of the type argument you may also pass an
expression of that type; this makes initialising a variable with
CONTAINER_OF easier.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
tools/libxl/libxl_internal.h | 29 +++++++++++++++++++++++++++++
1 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 594b9fb..213b5f9 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1238,6 +1238,35 @@ _hidden void libxl__ao__destroy(libxl_ctx*, libxl__ao *ao);
* Convenience macros.
*/

+/*
+ * CONTAINER_OF work like this. Given:
+ * typedef struct {
+ * ...
+ * member_type member_name;
+ * ...
+ * } outer_type;
+ * outer_type outer, *outer_var;
+ * member_type *inner_ptr = &outer->member_name;
+ *
+ * Then, effectively:
+ * outer_type *CONTAINER_OF(member_type *inner_ptr,
+ * *outer_var, // or type name for outer_type
+ * member_name);
+ *
+ * So that:
+ * CONTAINER_OF(inner_ptr, *outer_var, member_name) == &outer
+ * CONTAINER_OF(inner_ptr, outer_type, member_name) == &outer
+ */
+#define CONTAINER_OF(inner_ptr, outer, member_name) \
+ ({ \
+ typeof(outer) *container_of_; \
+ container_of_ = (void*)((char*)(inner_ptr) - \
+ offsetof(typeof(outer), member_name)); \
+ (void)(&container_of_->member_name == \
+ (typeof(inner_ptr))0) /* type check */; \
+ container_of_; \
+ })
+

/*
* All of these assume (or define)
--
1.7.2.5


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