[RFC PATCH 5/5] SUNRPC: pipefs per-net operations helper introduced

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

During per-net operation pipes creation and destruction we have to make sure,
that pipefs sb exists for the whole creation/destruction procedure.
This is done by using special mutex which controls pipefs sb reference on network namespace context.
Helper consist of two parts: first of them (rpc_get_dentry_net) searches for
dentry with specified name and returns with mutex taken on success. When pipe
creation is completed, caller should release this mutex by rpc_put_dentry_net
call.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>

---
 include/linux/sunrpc/rpc_pipe_fs.h |    5 ++++
 net/sunrpc/netns.h                 |    1 +
 net/sunrpc/rpc_pipe.c              |   41 ++++++++++++++++++++++++++++++++++++
 net/sunrpc/sunrpc_syms.c           |    1 +
 4 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/include/linux/sunrpc/rpc_pipe_fs.h b/include/linux/sunrpc/rpc_pipe_fs.h
index 4a327ad..d48ff0b 100644
--- a/include/linux/sunrpc/rpc_pipe_fs.h
+++ b/include/linux/sunrpc/rpc_pipe_fs.h
@@ -55,6 +55,11 @@ enum {
 extern struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 				      const unsigned char *dir_name);
 
+extern void rpc_pipefs_init_net(struct net *net);
+extern struct dentry *rpc_get_dentry_net(const struct net *net,
+					 const unsigned char *dir_name);
+extern void rpc_put_dentry_net(const struct net *net, struct dentry *dentry);
+
 extern int rpc_queue_upcall(struct inode *, struct rpc_pipe_msg *);
 
 struct rpc_clnt;
diff --git a/net/sunrpc/netns.h b/net/sunrpc/netns.h
index b384252..11d2f48 100644
--- a/net/sunrpc/netns.h
+++ b/net/sunrpc/netns.h
@@ -11,6 +11,7 @@ struct sunrpc_net {
 	struct cache_detail *ip_map_cache;
 
 	struct super_block *pipefs_sb;
+	struct mutex pipefs_sb_lock;
 };
 
 extern int sunrpc_net_id;
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index a873f03..331be28 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -1033,6 +1033,45 @@ struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 }
 EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);
 
+void rpc_pipefs_init_net(struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	mutex_init(&sn->pipefs_sb_lock);
+}
+
+/*
+ * This call will be used for per network namespace operations calls.
+ * Note: Function will be returned with pipefs_sb_lock taken if dentry was
+ * found. This lock have to be released by rpc_put_dentry_net() when all
+ * operations will be completed.
+ */
+struct dentry *rpc_get_dentry_net(const struct net *net,
+				  const unsigned char *dir_name)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+	struct dentry *dentry = ERR_PTR(-ENOENT);
+
+	mutex_lock(&sn->pipefs_sb_lock);
+	if (sn->pipefs_sb) {
+		dentry = rpc_d_lookup_sb(sn->pipefs_sb, dir_name);
+		if (dentry)
+			return dentry;
+	}
+	mutex_unlock(&sn->pipefs_sb_lock);
+	return ERR_PTR(-ENOENT);
+}
+EXPORT_SYMBOL_GPL(rpc_get_dentry_net);
+
+void rpc_put_dentry_net(const struct net *net, struct dentry *dentry)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	dput(dentry);
+	mutex_unlock(&sn->pipefs_sb_lock);
+}
+EXPORT_SYMBOL_GPL(rpc_put_dentry_net);
+
 static int
 rpc_fill_super(struct super_block *sb, void *data, int silent)
 {
@@ -1085,7 +1124,9 @@ void rpc_kill_sb(struct super_block *sb)
 	struct net *net = sb->s_fs_info;
 	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
 
+	mutex_lock(&sn->pipefs_sb_lock);
 	sn->pipefs_sb = NULL;
+	mutex_unlock(&sn->pipefs_sb_lock);
 	put_net(net);
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
 					   RPC_PIPEFS_UMOUNT,
diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c
index 9d08091..880de8b 100644
--- a/net/sunrpc/sunrpc_syms.c
+++ b/net/sunrpc/sunrpc_syms.c
@@ -38,6 +38,7 @@ static __net_init int sunrpc_init_net(struct net *net)
 	if (err)
 		goto err_ipmap;
 
+	rpc_pipefs_init_net(net);
 	return 0;
 
 err_ipmap: