datapath: Compatibility code for RCU check functions.

The rcu_dereference_rtnl() and rtnl_dereference() functions will
be introduced in 2.6.37.  They provide nice documentation of
locking expectations as well as checking on recent kernels.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

diff --git a/datapath/linux-2.6/compat-2.6/include/linux/rtnetlink.h b/datapath/linux-2.6/compat-2.6/include/linux/rtnetlink.h
index 6602536..b6bf7cb 100644 (file)
--- a/datapath/linux-2.6/compat-2.6/include/linux/rtnetlink.h
+++ b/datapath/linux-2.6/compat-2.6/include/linux/rtnetlink.h
@@ -46,4 +46,52 @@ static inline int rtnl_is_locked(void)
 
 #endif
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,34)
+#ifdef CONFIG_PROVE_LOCKING
+static inline int lockdep_rtnl_is_held(void)
+{
+       return 1;
+}
+#endif
+
+static inline int rcu_read_lock_held(void)
+{
+       return 1;
+}
+#endif
+
+#ifndef rcu_dereference_check
+#define rcu_dereference_check(p, c) rcu_dereference(p)
+#endif
+
+#ifndef rcu_dereference_protected
+#define rcu_dereference_protected(p, c) (p)
+#endif
+
+#ifndef rcu_dereference_rtnl
+/**
+ * rcu_dereference_rtnl - rcu_dereference with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Do an rcu_dereference(p), but check caller either holds rcu_read_lock()
+ * or RTNL. Note : Please prefer rtnl_dereference() or rcu_dereference()
+ */
+#define rcu_dereference_rtnl(p)                                        \
+       rcu_dereference_check(p, rcu_read_lock_held() ||        \
+                                lockdep_rtnl_is_held())
+#endif
+
+#ifndef rtnl_dereference
+/**
+ * rtnl_dereference - fetch RCU pointer when updates are prevented by RTNL
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Return the value of the specified RCU-protected pointer, but omit
+ * both the smp_read_barrier_depends() and the ACCESS_ONCE(), because
+ * caller holds RTNL.
+ */
+#define rtnl_dereference(p)                                    \
+       rcu_dereference_protected(p, lockdep_rtnl_is_held())
+#endif
+
 #endif /* linux/rtnetlink.h wrapper */