nfs41: sunrpc: provide functions to create and destroy a svc_xprt for backchannel use

For nfs41 callbacks we need an svc_xprt to process requests coming up the
backchannel socket as rpc_rqst's that are transformed into svc_rqst's that
need a rq_xprt to be processed.

The svc_{udp,tcp}_create methods are too heavy for this job as svc_create_socket
creates an actual socket to listen on while for nfs41 we're "reusing" the
fore channel's socket.
Signed-off-by: Benny Halevy <bhalevy@panasas.com>

include/linux/sunrpc/svcsock.h

@@ -42,6 +42,8 @@ int		svc_sock_names(char *buf, struct svc_serv *serv, char *toclose);
 int		svc_addsock(struct svc_serv *serv, int fd, char *name_return);
 void		svc_init_xprt_sock(void);
 void		svc_cleanup_xprt_sock(void);
+struct svc_xprt *svc_sock_create(struct svc_serv *serv, int prot);
+void		svc_sock_destroy(struct svc_xprt *);
 
 /*
  * svc_makesock socket characteristics

net/sunrpc/svcsock.c

@@ -1327,3 +1327,42 @@ static void svc_sock_free(struct svc_xprt *xprt)
 		sock_release(svsk->sk_sock);
 	kfree(svsk);
 }
+
+/*
+ * Create a svc_xprt.
+ *
+ * For internal use only (e.g. nfsv4.1 backchannel).
+ * Callers should typically use the xpo_create() method.
+ */
+struct svc_xprt *svc_sock_create(struct svc_serv *serv, int prot)
+{
+	struct svc_sock *svsk;
+	struct svc_xprt *xprt = NULL;
+
+	dprintk("svc: %s\n", __func__);
+	svsk = kzalloc(sizeof(*svsk), GFP_KERNEL);
+	if (!svsk)
+		goto out;
+
+	xprt = &svsk->sk_xprt;
+	if (prot == IPPROTO_TCP)
+		svc_xprt_init(&svc_tcp_class, xprt, serv);
+	else if (prot == IPPROTO_UDP)
+		svc_xprt_init(&svc_udp_class, xprt, serv);
+	else
+		BUG();
+out:
+	dprintk("svc: %s return %p\n", __func__, xprt);
+	return xprt;
+}
+EXPORT_SYMBOL_GPL(svc_sock_create);
+
+/*
+ * Destroy a svc_sock.
+ */
+void svc_sock_destroy(struct svc_xprt *xprt)
+{
+	if (xprt)
+		kfree(container_of(xprt, struct svc_sock, sk_xprt));
+}
+EXPORT_SYMBOL_GPL(svc_sock_destroy);