SUNRPC: subscribe RPC clients to pipefs notifications

This patch subscribes RPC clients to RPC pipefs notifications. RPC clients
notifier block is registering with pipefs initialization during SUNRPC module
init.
This notifier callback is responsible for RPC client PipeFS directory and GSS
pipes creation. For pipes creation and destruction two additional callbacks
were added to struct rpc_authops.
Note that no locking required in notifier callback because PipeFS superblock
pointer is passed as an argument from it's creation or destruction routine and
thus we can be sure about it's validity.

Signed-off-by: Stanislav Kinsbursky <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>

include/linux/sunrpc/auth.h

···
 
 	struct rpc_cred *	(*lookup_cred)(struct rpc_auth *, struct auth_cred *, int);
 	struct rpc_cred *	(*crcreate)(struct rpc_auth*, struct auth_cred *, int);
+	int			(*pipes_create)(struct rpc_auth *);
+	void			(*pipes_destroy)(struct rpc_auth *);
 };
 
 struct rpc_credops {

net/sunrpc/auth_gss/auth_gss.c

···
 	struct gss_auth *gss_auth;
 
 	gss_auth = container_of(auth, struct gss_auth, rpc_auth);
-	rpc_unlink(gss_auth->pipe[0]->dentry);
-	rpc_unlink(gss_auth->pipe[1]->dentry);
+	if (gss_auth->pipe[0]->dentry)
+		rpc_unlink(gss_auth->pipe[0]->dentry);
+	if (gss_auth->pipe[1]->dentry)
+		rpc_unlink(gss_auth->pipe[1]->dentry);
 }
 
 static int gss_pipes_dentries_create(struct rpc_auth *auth)
···
 	.create		= gss_create,
 	.destroy	= gss_destroy,
 	.lookup_cred	= gss_lookup_cred,
-	.crcreate	= gss_create_cred
+	.crcreate	= gss_create_cred,
+	.pipes_create	= gss_pipes_dentries_create,
+	.pipes_destroy	= gss_pipes_dentries_destroy,
 };
 
 static const struct rpc_credops gss_credops = {

net/sunrpc/clnt.c

···
 
 static void __rpc_clnt_remove_pipedir(struct rpc_clnt *clnt)
 {
-	if (clnt->cl_path.dentry)
+	if (clnt->cl_path.dentry) {
+		if (clnt->cl_auth && clnt->cl_auth->au_ops->pipes_destroy)
+			clnt->cl_auth->au_ops->pipes_destroy(clnt->cl_auth);
 		rpc_remove_client_dir(clnt->cl_path.dentry);
+	}
 	clnt->cl_path.dentry = NULL;
 }
 
···
 	}
 	clnt->cl_path = path;
 	return 0;
+}
+
+static int __rpc_pipefs_event(struct rpc_clnt *clnt, unsigned long event,
+				struct super_block *sb)
+{
+	struct dentry *dentry;
+	int err = 0;
+
+	switch (event) {
+	case RPC_PIPEFS_MOUNT:
+		if (clnt->cl_program->pipe_dir_name == NULL)
+			break;
+		dentry = rpc_setup_pipedir_sb(sb, clnt,
+					      clnt->cl_program->pipe_dir_name);
+		BUG_ON(dentry == NULL);
+		if (IS_ERR(dentry))
+			return PTR_ERR(dentry);
+		clnt->cl_path.dentry = dentry;
+		if (clnt->cl_auth->au_ops->pipes_create) {
+			err = clnt->cl_auth->au_ops->pipes_create(clnt->cl_auth);
+			if (err)
+				__rpc_clnt_remove_pipedir(clnt);
+		}
+		break;
+	case RPC_PIPEFS_UMOUNT:
+		__rpc_clnt_remove_pipedir(clnt);
+		break;
+	default:
+		printk(KERN_ERR "%s: unknown event: %ld\n", __func__, event);
+		return -ENOTSUPP;
+	}
+	return err;
+}
+
+static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
+			    void *ptr)
+{
+	struct super_block *sb = ptr;
+	struct rpc_clnt *clnt;
+	int error = 0;
+	struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);
+
+	spin_lock(&sn->rpc_client_lock);
+	list_for_each_entry(clnt, &sn->all_clients, cl_clients) {
+		error = __rpc_pipefs_event(clnt, event, sb);
+		if (error)
+			break;
+	}
+	spin_unlock(&sn->rpc_client_lock);
+	return error;
+}
+
+static struct notifier_block rpc_clients_block = {
+	.notifier_call	= rpc_pipefs_event,
+};
+
+int rpc_clients_notifier_register(void)
+{
+	return rpc_pipefs_notifier_register(&rpc_clients_block);
+}
+
+void rpc_clients_notifier_unregister(void)
+{
+	return rpc_pipefs_notifier_unregister(&rpc_clients_block);
 }
 
 static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, struct rpc_xprt *xprt)

net/sunrpc/rpc_pipe.c

···
 
 /**
  * rpc_remove_client_dir - Remove a directory created with rpc_create_client_dir()
- * @dentry: directory to remove
+ * @clnt: rpc client
  */
 int rpc_remove_client_dir(struct dentry *dentry)
 {
···
 				init_once);
 	if (!rpc_inode_cachep)
 		return -ENOMEM;
+	err = rpc_clients_notifier_register();
+	if (err)
+		goto err_notifier;
 	err = register_filesystem(&rpc_pipe_fs_type);
-	if (err) {
-		kmem_cache_destroy(rpc_inode_cachep);
-		return err;
-	}
-
+	if (err)
+		goto err_register;
 	return 0;
+
+err_register:
+	rpc_clients_notifier_unregister();
+err_notifier:
+	kmem_cache_destroy(rpc_inode_cachep);
+	return err;
 }
 
 void unregister_rpc_pipefs(void)
 {
+	rpc_clients_notifier_unregister();
 	kmem_cache_destroy(rpc_inode_cachep);
 	unregister_filesystem(&rpc_pipe_fs_type);
 }

net/sunrpc/sunrpc.h

···
 		    struct page *headpage, unsigned long headoffset,
 		    struct page *tailpage, unsigned long tailoffset);
 
+int rpc_clients_notifier_register(void);
+void rpc_clients_notifier_unregister(void);
 #endif /* _NET_SUNRPC_SUNRPC_H */