SUNRPC: send notification events on pipefs sb creation and destruction

They will be used to notify subscribers about pipefs superblock creation and
destruction.
Subcribers will have to create their dentries on passed superblock on mount
event and destroy otherwise.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/rpc_pipe_fs.h

@@ -43,6 +43,14 @@ RPC_I(struct inode *inode)
 	return container_of(inode, struct rpc_inode, vfs_inode);
 }
 
+extern int rpc_pipefs_notifier_register(struct notifier_block *);
+extern void rpc_pipefs_notifier_unregister(struct notifier_block *);
+
+enum {
+	RPC_PIPEFS_MOUNT,
+	RPC_PIPEFS_UMOUNT,
+};
+
 extern ssize_t rpc_pipe_generic_upcall(struct file *, struct rpc_pipe_msg *,
 				       char __user *, size_t);
 extern int rpc_queue_upcall(struct inode *, struct rpc_pipe_msg *);

net/sunrpc/rpc_pipe.c

@@ -28,8 +28,10 @@
 #include <linux/sunrpc/rpc_pipe_fs.h>
 #include <linux/sunrpc/cache.h>
 #include <linux/nsproxy.h>
+#include <linux/notifier.h>
 
 #include "netns.h"
+#include "sunrpc.h"
 
 static struct vfsmount *rpc_mnt __read_mostly;
 static int rpc_mount_count;
@@ -41,6 +43,20 @@ static struct kmem_cache *rpc_inode_cachep __read_mostly;
 
 #define RPC_UPCALL_TIMEOUT (30*HZ)
 
+static BLOCKING_NOTIFIER_HEAD(rpc_pipefs_notifier_list);
+
+int rpc_pipefs_notifier_register(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_cond_register(&rpc_pipefs_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(rpc_pipefs_notifier_register);
+
+void rpc_pipefs_notifier_unregister(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&rpc_pipefs_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(rpc_pipefs_notifier_unregister);
+
 static void rpc_purge_list(struct rpc_inode *rpci, struct list_head *head,
 		void (*destroy_msg)(struct rpc_pipe_msg *), int err)
 {
@@ -997,6 +1013,7 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
 	struct inode *inode;
 	struct dentry *root;
 	struct net *net = data;
+	int err;
 
 	sb->s_blocksize = PAGE_CACHE_SIZE;
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
@@ -1014,8 +1031,20 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
 	}
 	if (rpc_populate(root, files, RPCAUTH_lockd, RPCAUTH_RootEOF, NULL))
 		return -ENOMEM;
+	err = blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
+					   RPC_PIPEFS_MOUNT,
+					   sb);
+	if (err)
+		goto err_depopulate;
 	sb->s_fs_info = get_net(net);
 	return 0;
+
+err_depopulate:
+	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
+					   RPC_PIPEFS_UMOUNT,
+					   sb);
+	__rpc_depopulate(root, files, RPCAUTH_lockd, RPCAUTH_RootEOF);
+	return err;
 }
 
 static struct dentry *
@@ -1030,6 +1059,9 @@ void rpc_kill_sb(struct super_block *sb)
 	struct net *net = sb->s_fs_info;
 
 	put_net(net);
+	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
+					   RPC_PIPEFS_UMOUNT,
+					   sb);
 	kill_litter_super(sb);
 }