--- /dev/null
+Userspace RCU API
+by Mathieu Desnoyers and Paul E. McKenney
+
+
+void rcu_init(void);
+
+ This must be called before any of the following functions
+ are invoked.
+
+void rcu_read_lock(void);
+
+ Begin an RCU read-side critical section. These critical
+ sections may be nested.
+
+void rcu_read_unlock(void);
+
+ End an RCU read-side critical section.
+
+void rcu_register_thread(void);
+
+ Each thread must invoke this function before its first call to
+ rcu_read_lock(). Threads that never call rcu_read_lock() need
+ not invoke this function. In addition, rcu-bp ("bullet proof"
+ RCU) does not require any thread to invoke rcu_register_thread().
+
+void rcu_unregister_thread(void);
+
+ Each thread that invokes rcu_register_thread() must invoke
+ rcu_unregister_thread() before invoking pthread_exit()
+ or before returning from its top-level function.
+
+void synchronize_rcu(void);
+
+ Wait until every pre-existing RCU read-side critical section
+ has completed. Note that this primitive will not necessarily
+ wait for RCU read-side critical sections that have not yet
+ started: this is not a reader-writer lock. The duration
+ actually waited is called an RCU grace period.
+
+void call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *head));
+
+ Registers the callback indicated by "head". This means
+ that "func" will be invoked after the end of a future
+ RCU grace period. The rcu_head structure referenced
+ by "head" will normally be a field in a larger RCU-protected
+ structure. A typical implementation of "func" is as
+ follows:
+
+ void func(struct rcu_head *head)
+ {
+ struct foo *p = container_of(head, struct foo, rcu);
+
+ free(p);
+ }
+
+ This RCU callback function can be registered as follows
+ given a pointer "p" to the enclosing structure:
+
+ call_rcu(&p->rcu, func);
+
+ call_rcu should be called from registered RCU read-side threads.
+ For the QSBR flavor, the caller should be online.
+
+struct call_rcu_data *create_call_rcu_data(unsigned long flags,
+ int cpu_affinity);
+
+ Returns a handle that can be passed to the following
+ primitives. The "flags" argument can be zero, or can be
+ URCU_CALL_RCU_RT if the worker threads associated with the
+ new helper thread are to get real-time response. The argument
+ "cpu_affinity" specifies a cpu on which the call_rcu thread should
+ be affined to. It is ignored if negative.
+
+struct call_rcu_data *get_default_call_rcu_data(void);
+
+ Returns the handle of the default call_rcu() helper thread.
+
+struct call_rcu_data *get_call_rcu_data(void);
+
+ Returns the handle of the current thread's call_rcu() helper
+ thread, which might well be the default helper thread.
+ get_call_rcu_data should be called from registered RCU read-side
+ threads. For the QSBR flavor, the caller should be online.
+
+void call_rcu_data_free(struct call_rcu_data *crdp);
+
+ Terminates a call_rcu() helper thread and frees its associated
+ data. The caller must have ensured that this thread is no longer
+ in use, for example, by passing NULL to set_thread_call_rcu_data()
+ and set_cpu_call_rcu_data() as required.
+
+struct call_rcu_data *get_default_call_rcu_data(void);
+
+ Returns the handle for the default call_rcu() helper thread.
+ Creates it if necessary.
+
+struct call_rcu_data *get_cpu_call_rcu_data(int cpu);
+
+ Returns the handle for the current cpu's call_rcu() helper
+ thread, or NULL if the current CPU has no helper thread
+ currently assigned. The call to this function and use of the
+ returned call_rcu_data should be protected by RCU read-side
+ lock.
+
+struct call_rcu_data *get_thread_call_rcu_data(void);
+
+ Returns the handle for the current thread's hard-assigned
+ call_rcu() helper thread, or NULL if the current thread is
+ instead using a per-CPU or the default helper thread.
+
+struct call_rcu_data *get_call_rcu_data(void);
+
+ Returns the handle for the current thread's call_rcu() helper
+ thread, which is either, in increasing order of preference:
+ per-thread hard-assigned helper thread, per-cpu helper thread,
+ or default helper thread.
+
+pthread_t get_call_rcu_thread(struct call_rcu_data *crdp);
+
+ Returns the helper thread's pthread identifier linked to a call
+ rcu helper thread data.
+
+void set_thread_call_rcu_data(struct call_rcu_data *crdp);
+
+ Sets the current thread's hard-assigned call_rcu() helper to the
+ handle specified by "crdp". Note that "crdp" can be NULL to
+ disassociate this thread from its helper. Once a thread is
+ disassociated from its helper, further call_rcu() invocations
+ use the current CPU's helper if there is one and the default
+ helper otherwise.
+
+int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp);
+
+ Sets the specified CPU's call_rcu() helper to the handle
+ specified by "crdp". Again, "crdp" can be NULL to disassociate
+ this CPU from its helper thread. Once a CPU has been
+ disassociated from its helper, further call_rcu() invocations
+ that would otherwise have used this CPU's helper will instead
+ use the default helper. The caller must wait for a grace-period
+ to pass between return from set_cpu_call_rcu_data() and call to
+ call_rcu_data_free() passing the previous call rcu data as
+ argument.
+
+int create_all_cpu_call_rcu_data(unsigned long flags)
+
+ Creates a separate call_rcu() helper thread for each CPU.
+ After this primitive is invoked, the global default call_rcu()
+ helper thread will not be called.
+
+ The set_thread_call_rcu_data(), set_cpu_call_rcu_data(), and
+ create_all_cpu_call_rcu_data() functions may be combined to set up
+ pretty much any desired association between worker and call_rcu()
+ helper threads. If a given executable calls only call_rcu(),
+ then that executable will have only the single global default
+ call_rcu() helper thread. This will suffice in most cases.
+
+void free_all_cpu_call_rcu_data(void);
+
+ Clean up all the per-CPU call_rcu threads. Should be paired with
+ create_all_cpu_call_rcu_data() to perform teardown. Note that
+ this function invokes synchronize_rcu() internally, so the
+ caller should be careful not to hold mutexes (or mutexes within a
+ dependency chain) that are also taken within a RCU read-side
+ critical section, or in a section where QSBR threads are online.
+
+void call_rcu_after_fork_child(void);
+
+ Should be used as pthread_atfork() handler for programs using
+ call_rcu and performing fork() or clone() without a following
+ exec().
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