Subject: Re: [PATCH v6 1/8] SUNRPC: introduce helpers for reference counted rpcbind clients

From: Stanislav Kinsbursky <[email-masked]>
Date: Wed, 21 Sep 2011 13:07:43 +0400

v6:
1) added write memory barrier to rpcb_set_local to make sure, that rpcbind 
clients become valid before rpcb_users assignment
2) explicitly set rpcb_users to 1 instead of incrementing it (looks clearer from 
my pow).

Notice: write memory barrier after zeroing rpcbind clients in rpcb_put_local() 
is not required, since to users of them left. New user (service) will create new 
clients before dereferencing them.

This helpers will be used for dynamical creation and destruction of rpcbind
clients.
Variable rpcb_users is actually a counter of lauched RPC services. If rpcbind
clients has been created already, then we just increase rpcb_users.

Signed-off-by: Stanislav Kinsbursky <[email-masked]>

---
  net/sunrpc/rpcb_clnt.c |   54 ++++++++++++++++++++++++++++++++++++++++++++++++
  1 files changed, 54 insertions(+), 0 deletions(-)

diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
index e45d2fb..9fcdb42 100644
--- a/net/sunrpc/rpcb_clnt.c
+++ b/net/sunrpc/rpcb_clnt.c
@@ -114,6 +114,9 @@ static struct rpc_program	rpcb_program;
  static struct rpc_clnt *	rpcb_local_clnt;
  static struct rpc_clnt *	rpcb_local_clnt4;

+DEFINE_SPINLOCK(rpcb_clnt_lock);
+unsigned int			rpcb_users;
+
  struct rpcbind_args {
  	struct rpc_xprt *	r_xprt;

@@ -161,6 +164,57 @@ static void rpcb_map_release(void *data)
  	kfree(map);
  }

+static int rpcb_get_local(void)
+{
+	int cnt;
+
+	spin_lock(&rpcb_clnt_lock);
+	if (rpcb_users)
+		rpcb_users++;
+	cnt = rpcb_users;
+	spin_unlock(&rpcb_clnt_lock);
+
+	return cnt;
+}
+
+void rpcb_put_local(void)
+{
+	struct rpc_clnt *clnt = rpcb_local_clnt;
+	struct rpc_clnt *clnt4 = rpcb_local_clnt4;
+	int shutdown;
+
+	spin_lock(&rpcb_clnt_lock);
+	if (--rpcb_users == 0) {
+		rpcb_local_clnt = NULL;
+		rpcb_local_clnt4 = NULL;
+	}
+	shutdown = !rpcb_users;
+	spin_unlock(&rpcb_clnt_lock);
+
+	if (shutdown) {
+		/*
+		 * cleanup_rpcb_clnt - remove xprtsock's sysctls, unregister
+		 */
+		if (clnt4)
+			rpc_shutdown_client(clnt4);
+		if (clnt)
+			rpc_shutdown_client(clnt);
+	}
+	return;
+}
+
+static void rpcb_set_local(struct rpc_clnt *clnt, struct rpc_clnt *clnt4)
+{
+	/* Protected by rpcb_create_local_mutex */
+	rpcb_local_clnt = clnt;
+	rpcb_local_clnt4 = clnt4;
+	smp_wmb();
+	rpcb_users = 1;
+	dprintk("RPC:       created new rpcb local clients (rpcb_local_clnt: "
+			"%p, rpcb_local_clnt4: %p)\n", rpcb_local_clnt,
+			rpcb_local_clnt4);
+}
+
  /*
   * Returns zero on success, otherwise a negative errno value
   * is returned.