[PATCH] RPC: Make rpc_create_client() probe server for RPC program+version support

 Ensure that we don't create an RPC client without checking that the server
 does indeed support the RPC program + version that we are trying to set up.

 This enables us to immediately return an error to "mount" if it turns out
 that the server is only supporting NFSv2, when we requested NFSv3 or NFSv4.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 59 insertions, 2 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 99515d7727a..b36797ad808 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -97,7 +97,7 @@ rpc_setup_pipedir(struct rpc_clnt *clnt, char *dir_name)
  * made to sleep too long.
  */
 struct rpc_clnt *
-rpc_create_client(struct rpc_xprt *xprt, char *servname,
+rpc_new_client(struct rpc_xprt *xprt, char *servname,
 		  struct rpc_program *program, u32 vers,
 		  rpc_authflavor_t flavor)
 {
@@ -182,6 +182,36 @@ out_err:
 	return ERR_PTR(err);
 }
 
+/**
+ * Create an RPC client
+ * @xprt - pointer to xprt struct
+ * @servname - name of server
+ * @info - rpc_program
+ * @version - rpc_program version
+ * @authflavor - rpc_auth flavour to use
+ *
+ * Creates an RPC client structure, then pings the server in order to
+ * determine if it is up, and if it supports this program and version.
+ *
+ * This function should never be called by asynchronous tasks such as
+ * the portmapper.
+ */
+struct rpc_clnt *rpc_create_client(struct rpc_xprt *xprt, char *servname,
+		struct rpc_program *info, u32 version, rpc_authflavor_t authflavor)
+{
+	struct rpc_clnt *clnt;
+	int err;
+	
+	clnt = rpc_new_client(xprt, servname, info, version, authflavor);
+	if (IS_ERR(clnt))
+		return clnt;
+	err = rpc_ping(clnt, RPC_TASK_SOFT|RPC_TASK_NOINTR);
+	if (err == 0)
+		return clnt;
+	rpc_shutdown_client(clnt);
+	return ERR_PTR(err);
+}
+
 /*
  * This function clones the RPC client structure. It allows us to share the
  * same transport while varying parameters such as the authentication
@@ -1086,3 +1116,30 @@ out_overflow:
 	printk(KERN_WARNING "RPC %s: server reply was truncated.\n", __FUNCTION__);
 	goto out_retry;
 }
+
+static int rpcproc_encode_null(void *rqstp, u32 *data, void *obj)
+{
+	return 0;
+}
+
+static int rpcproc_decode_null(void *rqstp, u32 *data, void *obj)
+{
+	return 0;
+}
+
+static struct rpc_procinfo rpcproc_null = {
+	.p_encode = rpcproc_encode_null,
+	.p_decode = rpcproc_decode_null,
+};
+
+int rpc_ping(struct rpc_clnt *clnt, int flags)
+{
+	struct rpc_message msg = {
+		.rpc_proc = &rpcproc_null,
+	};
+	int err;
+	msg.rpc_cred = authnull_ops.lookup_cred(NULL, NULL, 0);
+	err = rpc_call_sync(clnt, &msg, flags);
+	put_rpccred(msg.rpc_cred);
+	return err;
+}
diff --git a/net/sunrpc/pmap_clnt.c b/net/sunrpc/pmap_clnt.c
index 97c420ff1ee..df4d84c9020 100644
--- a/net/sunrpc/pmap_clnt.c
+++ b/net/sunrpc/pmap_clnt.c
@@ -207,7 +207,7 @@ pmap_create(char *hostname, struct sockaddr_in *srvaddr, int proto)
 	xprt->addr.sin_port = htons(RPC_PMAP_PORT);
 
 	/* printk("pmap: create clnt\n"); */
-	clnt = rpc_create_client(xprt, hostname,
+	clnt = rpc_new_client(xprt, hostname,
 				&pmap_program, RPC_PMAP_VERSION,
 				RPC_AUTH_UNIX);
 	if (!IS_ERR(clnt)) {