SUNRPC: Add a helper to switch the transport of an rpc_clnt

Commit Message

Chuck Lever July 19, 2013, 6 p.m. UTC

From: Trond Myklebust <[e-mail]>

Signed-off-by: Trond Myklebust <[e-mail]>
[ cel: forward ported to 3.11 ]
Signed-off-by: Chuck Lever <[e-mail]>
---

I changed this patch slightly to ensure that on an error return,
rpc_switch_client_transport() hasn't mangled the clnt so that it
cannot be used again.

I don't want to leave the upper layers with a clnt that can't be
used for a retry, or that might cause an unexplained hang rather
than an immediate error exit.

Does this seem reasonable?


 include/linux/sunrpc/clnt.h |    4 ++
 net/sunrpc/clnt.c           |   87 ++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 85 insertions(+), 6 deletions(-)


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Patch

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index bfe11be..29bb018 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -134,6 +134,10 @@  void rpc_task_reset_client(struct rpc_task *task, struct rpc_clnt *clnt);
 struct rpc_clnt *rpc_clone_client(struct rpc_clnt *);
 struct rpc_clnt *rpc_clone_client_set_auth(struct rpc_clnt *,
 				rpc_authflavor_t);
+int		rpc_switch_client_transport(struct rpc_clnt *,
+				struct xprt_create *,
+				const struct rpc_timeout *);
+
 void		rpc_shutdown_client(struct rpc_clnt *);
 void		rpc_release_client(struct rpc_clnt *);
 void		rpc_task_release_client(struct rpc_task *);
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 5a750b9..3efd363 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -25,6 +25,7 @@ 
 #include <linux/namei.h>
 #include <linux/mount.h>
 #include <linux/slab.h>
+#include <linux/rcupdate.h>
 #include <linux/utsname.h>
 #include <linux/workqueue.h>
 #include <linux/in.h>
@@ -289,12 +290,32 @@  static void rpc_clnt_set_nodename(struct rpc_clnt *clnt, const char *nodename)
 	memcpy(clnt->cl_nodename, nodename, clnt->cl_nodelen);
 }
 
+static struct rpc_xprt *rpc_clnt_set_transport(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		const struct rpc_timeout *timeout)
+{
+	struct rpc_xprt *old;
+
+	spin_lock(&clnt->cl_lock);
+	old = rcu_dereference(clnt->cl_xprt);
+
+	if (!xprt_bound(xprt))
+		clnt->cl_autobind = 1;
+
+	clnt->cl_timeout = timeout;
+	rcu_assign_pointer(clnt->cl_xprt, xprt);
+	spin_unlock(&clnt->cl_lock);
+
+	return old;
+}
+
 static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, struct rpc_xprt *xprt)
 {
 	const struct rpc_program *program = args->program;
 	const struct rpc_version *version;
 	struct rpc_clnt		*clnt = NULL;
 	struct rpc_auth		*auth;
+	const struct rpc_timeout *timeout;
 	int err;
 
 	/* sanity check the name before trying to print it */
@@ -318,7 +339,6 @@  static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 		goto out_err;
 	clnt->cl_parent = clnt;
 
-	rcu_assign_pointer(clnt->cl_xprt, xprt);
 	clnt->cl_procinfo = version->procs;
 	clnt->cl_maxproc  = version->nrprocs;
 	clnt->cl_protname = program->name;
@@ -333,16 +353,15 @@  static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 	INIT_LIST_HEAD(&clnt->cl_tasks);
 	spin_lock_init(&clnt->cl_lock);
 
-	if (!xprt_bound(xprt))
-		clnt->cl_autobind = 1;
-
-	clnt->cl_timeout = xprt->timeout;
+	timeout = xprt->timeout;
 	if (args->timeout != NULL) {
 		memcpy(&clnt->cl_timeout_default, args->timeout,
 				sizeof(clnt->cl_timeout_default));
-		clnt->cl_timeout = &clnt->cl_timeout_default;
+		timeout = &clnt->cl_timeout_default;
 	}
 
+	rpc_clnt_set_transport(clnt, xprt, timeout);
+
 	clnt->cl_rtt = &clnt->cl_rtt_default;
 	rpc_init_rtt(&clnt->cl_rtt_default, clnt->cl_timeout->to_initval);
 	clnt->cl_principal = NULL;
@@ -573,6 +592,62 @@  rpc_clone_client_set_auth(struct rpc_clnt *clnt, rpc_authflavor_t flavor)
 }
 EXPORT_SYMBOL_GPL(rpc_clone_client_set_auth);
 
+/**
+ * rpc_switch_client_transport: switch the RPC transport on the fly
+ * @clnt: pointer to a struct rpc_clnt
+ * @args: pointer to the new transport arguments
+ * @timeout: pointer to the new timeout parameters
+ *
+ * This function allows the caller to switch the RPC transport for the
+ * rpc_clnt structure 'clnt' to allow it to connect to a mirrored NFS
+ * server, for instance.  It assumes that the caller has ensured that
+ * there are no active tasks by using some form of locking.
+ *
+ * Returns zero if "clnt" is now using the new xprt.  Otherwise a
+ * negative errno is returned, and "clnt" continues to use the old
+ * xprt.
+ */
+int rpc_switch_client_transport(struct rpc_clnt *clnt,
+		struct xprt_create *args,
+		const struct rpc_timeout *timeout)
+{
+	const struct rpc_timeout *old_timeo;
+	rpc_authflavor_t pseudoflavor;
+	struct rpc_xprt *xprt, *old;
+	struct rpc_auth *auth;
+
+	xprt = xprt_create_transport(args);
+	if (IS_ERR(xprt)) {
+		dprintk("RPC:      failed to switch xprt for clnt %p\n", clnt);
+		return PTR_ERR(xprt);
+	}
+
+	pseudoflavor = clnt->cl_auth->au_flavor;
+
+	old_timeo = clnt->cl_timeout;
+	old = rpc_clnt_set_transport(clnt, xprt, timeout);
+
+	/*
+	 * Note: we must always create a new rpc_auth cache
+	 * when switching to a different server!  GSS contexts
+	 * in particular are between a single client and
+	 * server.
+	 */
+	auth = rpcauth_create(pseudoflavor, clnt);
+	if (IS_ERR(auth)) {
+		printk(KERN_INFO "RPC: Couldn't create auth handle (flavor %u)\n",
+				pseudoflavor);
+		rpc_clnt_set_transport(clnt, old, old_timeo);
+		xprt_put(xprt);
+		return PTR_ERR(auth);
+	}
+
+	synchronize_rcu();
+	xprt_put(old);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rpc_switch_client_transport);
+
 /*
  * Kill all tasks for the given client.
  * XXX: kill their descendants as well?