Author: ed
Date: Thu Sep 13 08:13:01 2012
New Revision: 240450
URL: http://svn.freebsd.org/changeset/base/240450
Log:
Rename __member2struct() to __containerof().
Compared to __member2struct(), this macro has the following advantages:
- It ensures that the type of the pointer is compatible with the member
field of the structure (or a void pointer).
- It works properly in combination with volatile and const, though
unfortunately it drops these qualifiers from the returned value.
mdf@ proposed to add the container_of() macro, just like Linux has.
Eventually I decided against this, as <sys/param.h> is included all over
the place. It seems container_of() on Linux is specific to the kernel,
not userspace. I'd rather not pollute userspace with this.
I also thought about adding __container_of(), but this would have two
advantages. Xorg seems to already have a __container_of(), which is not
compatible with this version. Also, the underscore in the middle
conflicts with our existing macros (__offsetof, __rangeof, etc).
I'm changing member2struct() to use its old code, as the extra
strictness of this new macro conflicts with existing code (read: cxgb).
MFC after: 1 month
Modified:
head/sys/sys/cdefs.h
head/sys/sys/param.h
head/sys/sys/queue.h
Modified: head/sys/sys/cdefs.h
==============================================================================
--- head/sys/sys/cdefs.h Thu Sep 13 07:25:41 2012 (r240449)
+++ head/sys/sys/cdefs.h Thu Sep 13 08:13:01 2012 (r240450)
@@ -402,8 +402,22 @@
#endif
#define __rangeof(type, start, end) \
(__offsetof(type, end) - __offsetof(type, start))
-#define __member2struct(s, m, x)
\
- ((struct s *)(void *)((char *)(x) - __offsetof(struct s, m)))
+
+/*
+ * Given the pointer x to the member m of the struct s, return
+ * a pointer to the containing structure. When using GCC, we first
+ * assign pointer x to a local variable, to check that its type is
+ * compatible with member m.
+ */
+#if __GNUC_PREREQ__(3, 1)
+#define __containerof(x, s, m) ({
\
+ const volatile __typeof(((s *)0)->m) *__x = (x); \
+ __DEQUALIFY(s *, (const volatile char *)__x - __offsetof(s, m));\
+})
+#else
+#define __containerof(x, s, m)
\
+ __DEQUALIFY(s *, (const volatile char *)(x) - __offsetof(s, m))
+#endif
/*
* Compiler-dependent macros to declare that functions take printf-like
Modified: head/sys/sys/param.h
==============================================================================
--- head/sys/sys/param.h Thu Sep 13 07:25:41 2012 (r240449)
+++ head/sys/sys/param.h Thu Sep 13 08:13:01 2012 (r240450)
@@ -331,10 +331,10 @@ __END_DECLS
((db) << (PAGE_SHIFT - DEV_BSHIFT))
/*
- * Given the pointer x to the member m of the struct s, return
- * a pointer to the containing structure.
+ * Old spelling of __containerof().
*/
-#define member2struct(s, m, x) __member2struct(s, m, x)
+#define member2struct(s, m, x)
\
+ ((struct s *)(void *)((char *)(x) - offsetof(struct s, m)))
/*
* Access a variable length array that has been declared as a fixed
Modified: head/sys/sys/queue.h
==============================================================================
--- head/sys/sys/queue.h Thu Sep 13 07:25:41 2012 (r240449)
+++ head/sys/sys/queue.h Thu Sep 13 08:13:01 2012 (r240450)
@@ -287,9 +287,8 @@ struct {
\
} while (0)
#define STAILQ_LAST(head, type, field)
\
- (STAILQ_EMPTY((head)) ? \
- NULL : \
- __member2struct(type, field.stqe_next, (head)->stqh_last))
+ (STAILQ_EMPTY((head)) ? NULL : \
+ __containerof((head)->stqh_last, struct type, field.stqe_next))
#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
@@ -425,9 +424,8 @@ struct {
\
#define LIST_NEXT(elm, field) ((elm)->field.le_next)
#define LIST_PREV(elm, head, type, field)
\
- ((elm)->field.le_prev == &LIST_FIRST((head)) ? \
- NULL : \
- __member2struct(type, field.le_next, (elm)->field.le_prev))
+ ((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL : \
+ __containerof((elm)->field.le_prev, struct type, field.le_next))
#define LIST_REMOVE(elm, field) do {
\
QMD_SAVELINK(oldnext, (elm)->field.le_next); \
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