[src/trunk]: src/sys Add container_of to libkern.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/bc0dab24ea0e
branches:  trunk
changeset: 337580:bc0dab24ea0e
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Apr 20 15:22:17 2015 +0000

description:
Add container_of to libkern.

Given x = &c->f, container_of(x, T, f) yields c, where T is the type
of c.

Discussed on tech-kern a while ago:

https://mail-index.netbsd.org/tech-kern/2013/03/21/msg015131.html

diffstat:

 sys/external/bsd/common/include/linux/kernel.h |  14 ++---------
 sys/lib/libkern/libkern.h                      |  29 +++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 12 deletions(-)

diffs (78 lines):

diff -r b83111b60da4 -r bc0dab24ea0e sys/external/bsd/common/include/linux/kernel.h
--- a/sys/external/bsd/common/include/linux/kernel.h    Mon Apr 20 15:18:59 2015 +0000
+++ b/sys/external/bsd/common/include/linux/kernel.h    Mon Apr 20 15:22:17 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kernel.h,v 1.6 2015/02/25 15:50:16 riastradh Exp $     */
+/*     $NetBSD: kernel.h,v 1.7 2015/04/20 15:22:18 riastradh Exp $     */
 
 /*-
  * Copyright (c) 2013 The NetBSD Foundation, Inc.
@@ -37,6 +37,8 @@
 #include <sys/param.h>
 #include <sys/systm.h>
 
+#include <lib/libkern/libkern.h>
+
 #define        oops_in_progress        (panicstr != NULL)
 
 #define        IS_ENABLED(option)      0 /* XXX Hmm...  */
@@ -94,16 +96,6 @@
 #define        upper_32_bits(X)        ((uint32_t) (((X) >> 16) >> 16))
 #define        lower_32_bits(X)        ((uint32_t) ((X) & 0xffffffffUL))
 
-/*
- * Given x = &c->f, container_of(x, T, f) gives us back c, where T is
- * the type of c.
- */
-#define        container_of(PTR, TYPE, FIELD)                                  \
-       ((TYPE *)(((char *)(PTR)) - offsetof(TYPE, FIELD) +             \
-           0*sizeof((PTR) -                                            \
-               &((TYPE *)(((char *)(PTR)) -                            \
-                       offsetof(TYPE, FIELD)))->FIELD)))
-
 #define        ARRAY_SIZE(ARRAY)       __arraycount(ARRAY)
 
 #define        swap(X, Y)      do                                              \
diff -r b83111b60da4 -r bc0dab24ea0e sys/lib/libkern/libkern.h
--- a/sys/lib/libkern/libkern.h Mon Apr 20 15:18:59 2015 +0000
+++ b/sys/lib/libkern/libkern.h Mon Apr 20 15:22:17 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: libkern.h,v 1.117 2015/01/16 18:36:31 christos Exp $   */
+/*     $NetBSD: libkern.h,v 1.118 2015/04/20 15:22:17 riastradh Exp $  */
 
 /*-
  * Copyright (c) 1992, 1993
@@ -309,6 +309,33 @@
 #endif
 #endif
 
+/*
+ * Return the container of an embedded struct.  Given x = &c->f,
+ * container_of(x, T, f) yields c, where T is the type of c.  Example:
+ *
+ *     struct foo { ... };
+ *     struct bar {
+ *             int b_x;
+ *             struct foo b_foo;
+ *             ...
+ *     };
+ *
+ *     struct bar b;
+ *     struct foo *fp = b.b_foo;
+ *
+ * Now we can get at b from fp by:
+ *
+ *     struct bar *bp = container_of(fp, struct bar, b_foo);
+ *
+ * The 0*sizeof((PTR) - ...) causes the compiler to warn if the type of
+ * *fp does not match the type of struct bar::b_foo.
+ */
+#define        container_of(PTR, TYPE, FIELD)                                  \
+       ((TYPE *)(((char *)(PTR)) - offsetof(TYPE, FIELD) +             \
+           0*sizeof((PTR) -                                            \
+               &((TYPE *)(((char *)(PTR)) -                            \
+                       offsetof(TYPE, FIELD)))->FIELD)))
+
 #define        MTPRNG_RLEN             624
 struct mtprng_state {
        unsigned int mt_idx;