[ovs-dev] [PATCH v4 09/14] ofp-actions: Introduce macro for padding struct members.

Ben Pfaff blp at ovn.org
Fri Feb 19 08:34:19 UTC 2016


An upcoming commit will add another case where it's desirable to ensure
that a variable-length array is aligned on an 8-byte boundary.  This macro
makes that a little easier.

Signed-off-by: Ben Pfaff <blp at ovn.org>
CC: Joe Stringer <joe at ovn.org>
---
 lib/ofp-actions.h | 43 ++++++++++++++++++++++---------------------
 1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/lib/ofp-actions.h b/lib/ofp-actions.h
index 58d7857..24143d3 100644
--- a/lib/ofp-actions.h
+++ b/lib/ofp-actions.h
@@ -185,6 +185,19 @@ BUILD_ASSERT_DECL(sizeof(struct ofpact) == 4);
 #define OFPACT_ALIGNTO 8
 #define OFPACT_ALIGN(SIZE) ROUND_UP(SIZE, OFPACT_ALIGNTO)
 
+/* Expands to an anonymous union that contains:
+ *
+ *    - MEMBERS in a nested anonymous struct.
+ *
+ *    - An array as large as MEMBERS plus padding to a multiple of 8 bytes.
+ *
+ * The effect is to pad MEMBERS to a multiple of 8 bytes. */
+#define OFPACT_PADDED_MEMBERS(MEMBERS)                          \
+    union {                                                     \
+        struct { MEMBERS };                                     \
+        uint8_t pad[OFPACT_ALIGN(sizeof(struct { MEMBERS }))];  \
+    }
+
 /* Returns the ofpact following 'ofpact'. */
 static inline struct ofpact *
 ofpact_next(const struct ofpact *ofpact)
@@ -487,8 +500,7 @@ struct ofpact_meter {
  *
  * Used for OFPIT11_WRITE_ACTIONS. */
 struct ofpact_nest {
-    struct ofpact ofpact;
-    uint8_t pad[PAD_SIZE(sizeof(struct ofpact), OFPACT_ALIGNTO)];
+    OFPACT_PADDED_MEMBERS(struct ofpact ofpact;);
     struct ofpact actions[];
 };
 BUILD_ASSERT_DECL(offsetof(struct ofpact_nest, actions) % OFPACT_ALIGNTO == 0);
@@ -507,21 +519,6 @@ enum nx_conntrack_flags {
  * that the packet should not be recirculated. */
 #define NX_CT_RECIRC_NONE OFPTT_ALL
 
-/* We want to determine the size of these elements at compile time to ensure
- * actions alignment, but we also want to allow ofpact_conntrack to have
- * basic _put(), _get(), etc accessors defined below which access these
- * members directly from ofpact_conntrack. An anonymous struct will serve
- * both of these purposes. */
-#define CT_MEMBERS                      \
-struct {                                \
-    struct ofpact ofpact;               \
-    uint16_t flags;                     \
-    uint16_t zone_imm;                  \
-    struct mf_subfield zone_src;        \
-    uint16_t alg;                       \
-    uint8_t recirc_table;               \
-}
-
 #if !defined(IPPORT_FTP)
 #define	IPPORT_FTP  21
 #endif
@@ -530,10 +527,14 @@ struct {                                \
  *
  * Used for NXAST_CT. */
 struct ofpact_conntrack {
-    union {
-        CT_MEMBERS;
-        uint8_t pad[OFPACT_ALIGN(sizeof(CT_MEMBERS))];
-    };
+    OFPACT_PADDED_MEMBERS(
+        struct ofpact ofpact;
+        uint16_t flags;
+        uint16_t zone_imm;
+        struct mf_subfield zone_src;
+        uint16_t alg;
+        uint8_t recirc_table;
+    );
     struct ofpact actions[0];
 };
 BUILD_ASSERT_DECL(offsetof(struct ofpact_conntrack, actions)
-- 
2.1.3




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