[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>

fs/lockd/host.c

@@ -189,6 +189,8 @@ nlm_bind_host(struct nlm_host *host)
 			goto forgetit;
 
 		xprt_set_timeout(&xprt->timeout, 5, nlmsvc_timeout);
+		xprt->nocong = 1;	/* No congestion control for NLM */
+		xprt->resvport = 1;	/* NLM requires a reserved port */
 
 		/* Existing NLM servers accept AUTH_UNIX only */
 		clnt = rpc_create_client(xprt, host->h_name, &nlm_program,
@@ -196,8 +198,6 @@ nlm_bind_host(struct nlm_host *host)
 		if (IS_ERR(clnt))
 			goto forgetit;
 		clnt->cl_autobind = 1;	/* turn on pmap queries */
-		xprt->nocong = 1;	/* No congestion control for NLM */
-		xprt->resvport = 1;	/* NLM requires a reserved port */
 
 		host->h_rpcclnt = clnt;
 	}

fs/lockd/mon.c

@@ -115,6 +115,7 @@ nsm_create(void)
 	xprt = xprt_create_proto(IPPROTO_UDP, &sin, NULL);
 	if (IS_ERR(xprt))
 		return (struct rpc_clnt *)xprt;
+	xprt->resvport = 1;	/* NSM requires a reserved port */
 
 	clnt = rpc_create_client(xprt, "localhost",
 				&nsm_program, SM_VERSION,
@@ -124,7 +125,6 @@ nsm_create(void)
 	clnt->cl_softrtry = 1;
 	clnt->cl_chatty   = 1;
 	clnt->cl_oneshot  = 1;
-	xprt->resvport = 1;	/* NSM requires a reserved port */
 	return clnt;
 
 out_err:

include/linux/sunrpc/clnt.h

@@ -111,6 +111,9 @@ struct rpc_procinfo {
 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 *rpc_new_client(struct rpc_xprt *xprt, char *servname,
+				struct rpc_program *info,
+				u32 version, rpc_authflavor_t authflavor);
 struct rpc_clnt *rpc_clone_client(struct rpc_clnt *);
 int		rpc_shutdown_client(struct rpc_clnt *);
 int		rpc_destroy_client(struct rpc_clnt *);
@@ -129,6 +132,7 @@ void		rpc_clnt_sigmask(struct rpc_clnt *clnt, sigset_t *oldset);
 void		rpc_clnt_sigunmask(struct rpc_clnt *clnt, sigset_t *oldset);
 void		rpc_setbufsize(struct rpc_clnt *, unsigned int, unsigned int);
 size_t		rpc_max_payload(struct rpc_clnt *);
+int		rpc_ping(struct rpc_clnt *clnt, int flags);
 
 static __inline__
 int rpc_call(struct rpc_clnt *clnt, u32 proc, void *argp, void *resp, int flags)

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 @@ rpc_create_client(struct rpc_xprt *xprt, char *servname,
 	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 @@ call_verify(struct rpc_task *task)
 	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;
+}

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)) {