[ovs-dev] [nlsize v2 2/2] datapath: Better calculate max nlattr-formatted flow size.

Justin Pettit jpettit at nicira.com
Mon Feb 7 23:13:00 UTC 2011


Both userspace and the kernel allocate space based on the max size of a
nlattr-formatted flow.  It was easy to change the max size of a flow
definition and cause crashes by forgetting to update one or both of
those definitions.  This commit attempts to make that harder by
providing a better description of how the max size is calculated and
defining that size in datapath-protocol.h and have the others use it.

Signed-off-by: Justin Pettit <jpettit at nicira.com>
---
 datapath/flow.c |    5 +++++
 datapath/flow.h |   17 +++++++++++++++--
 lib/odp-util.h  |   27 +++++++++++++++++++++++----
 3 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/datapath/flow.c b/datapath/flow.c
index 735e147..512b8f9 100644
--- a/datapath/flow.c
+++ b/datapath/flow.c
@@ -813,6 +813,11 @@ int flow_to_nlattrs(const struct sw_flow_key *swkey, struct sk_buff *skb)
 	struct odp_key_ethernet *eth_key;
 	struct nlattr *nla;
 
+	/* This is an imperfect sanity-check that FLOW_BUFSIZE doesn't need
+	 * to be updated, but will at least raise awareness when new ODP key
+	 * types are added. */
+	BUILD_BUG_ON(__ODP_KEY_ATTR_MAX != 14);
+
 	if (swkey->tun_id != cpu_to_be64(0))
 		NLA_PUT_BE64(skb, ODP_KEY_ATTR_TUN_ID, swkey->tun_id);
 
diff --git a/datapath/flow.h b/datapath/flow.h
index 9cf5c67..eba730f 100644
--- a/datapath/flow.h
+++ b/datapath/flow.h
@@ -107,8 +107,21 @@ u64 flow_used_time(unsigned long flow_jiffies);
 u32 flow_hash(const struct sw_flow_key *);
 int flow_cmp(const struct tbl_node *, void *target);
 
-/* By my calculations currently the longest valid nlattr-formatted flow key is
- * 132 bytes long.
+/* Upper bound on the length of a nlattr-formatted flow key.  The longest
+ * nlattr-formatted flow key would be:
+ *
+ *                         struct  pad  nl hdr  total
+ *                         ------  ---  ------  -----
+ *  ODP_KEY_ATTR_TUN_ID        8    --     4     12 
+ *  ODP_KEY_ATTR_IN_PORT       4    --     4      8
+ *  ODP_KEY_ATTR_ETHERNET     12    --     4     16
+ *  ODP_KEY_ATTR_8021Q         4    --     4      8
+ *  ODP_KEY_ATTR_ETHERTYPE     2     2     4      8
+ *  ODP_KEY_ATTR_IPV6         34     2     4     40 
+ *  ODP_KEY_ATTR_ICMPV6        2     2     4      8
+ *  ODP_KEY_ATTR_ND           28    --     4     32
+ *  -------------------------------------------------
+ *  total                                       132
  */
 #define FLOW_BUFSIZE 132
 
diff --git a/lib/odp-util.h b/lib/odp-util.h
index d991b19..4c59035 100644
--- a/lib/odp-util.h
+++ b/lib/odp-util.h
@@ -63,14 +63,33 @@ void format_odp_action(struct ds *, const struct nlattr *);
 void format_odp_actions(struct ds *, const struct nlattr *odp_actions,
                         size_t actions_len);
 
-/* By my calculations currently the longest valid nlattr-formatted flow key is
- * 132 bytes long.
+/* Upper bound on the length of a nlattr-formatted flow key.  The longest
+ * nlattr-formatted flow key would be:
  *
- * We allocate temporary on-stack buffers for flow keys as arrays of uint32_t
+ *                         struct  pad  nl hdr  total
+ *                         ------  ---  ------  -----
+ *  ODP_KEY_ATTR_TUN_ID        8    --     4     12 
+ *  ODP_KEY_ATTR_IN_PORT       4    --     4      8
+ *  ODP_KEY_ATTR_ETHERNET     12    --     4     16
+ *  ODP_KEY_ATTR_8021Q         4    --     4      8
+ *  ODP_KEY_ATTR_ETHERTYPE     2     2     4      8
+ *  ODP_KEY_ATTR_IPV6         34     2     4     40 
+ *  ODP_KEY_ATTR_ICMPV6        2     2     4      8
+ *  ODP_KEY_ATTR_ND           28    --     4     32
+ *  -------------------------------------------------
+ *  total                                       132
+ */
+#define ODPUTIL_FLOW_KEY_BYTES 132
+
+/* This is an imperfect sanity-check that ODPUTIL_FLOW_KEY_BYTES doesn't
+ * need to be updated, but will at least raise awareness when new ODP
+ * key types are added. */
+BUILD_ASSERT_DECL(__ODP_KEY_ATTR_MAX == 14);
+
+/* We allocate temporary on-stack buffers for flow keys as arrays of uint32_t
  * to ensure proper 32-bit alignment for Netlink attributes.  (An array of
  * "struct nlattr" might not, in theory, be sufficiently aligned because it
  * only contains 16-bit types.) */
-#define ODPUTIL_FLOW_KEY_BYTES 132
 #define ODPUTIL_FLOW_KEY_U32S DIV_ROUND_UP(ODPUTIL_FLOW_KEY_BYTES, 4)
 
 void odp_flow_key_format(const struct nlattr *, size_t, struct ds *);
-- 
1.7.1





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