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Rename __member2struct() to __containerof().

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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
This commit is contained in:
Ed Schouten 2012-09-13 08:13:01 +00:00
parent 03a51ef8f4
commit 5b5d76847d
3 changed files with 23 additions and 11 deletions
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18
sys/sys/cdefs.h
View File

@ -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

6
sys/sys/param.h
View File

@ -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

10
sys/sys/queue.h
View File

@ -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); \