vfs: Convert rpc_pipefs to use the new mount API

Convert the rpc_pipefs filesystem to the new internal mount API as the old
one will be obsoleted and removed.  This allows greater flexibility in
communication of mount parameters between userspace, the VFS and the
filesystem.

See Documentation/filesystems/mount_api.txt for more information.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Trond Myklebust <trond.myklebust@hammerspace.com>
cc: Anna Schumaker <anna.schumaker@netapp.com>
cc: "J. Bruce Fields" <bfields@fieldses.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-nfs@vger.kernel.org

net/sunrpc/rpc_pipe.c

@@ -13,6 +13,7 @@
 #include <linux/string.h>
 #include <linux/pagemap.h>
 #include <linux/mount.h>
+#include <linux/fs_context.h>
 #include <linux/namei.h>
 #include <linux/fsnotify.h>
 #include <linux/kernel.h>
@@ -1347,11 +1348,11 @@ rpc_gssd_dummy_depopulate(struct dentry *pipe_dentry)
 }
 
 static int
-rpc_fill_super(struct super_block *sb, void *data, int silent)
+rpc_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct inode *inode;
 	struct dentry *root, *gssd_dentry;
-	struct net *net = get_net(sb->s_fs_info);
+	struct net *net = sb->s_fs_info;
 	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
 	int err;
 
@@ -1408,12 +1409,29 @@ gssd_running(struct net *net)
 }
 EXPORT_SYMBOL_GPL(gssd_running);
 
-static struct dentry *
-rpc_mount(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *data)
+static int rpc_fs_get_tree(struct fs_context *fc)
+{
+	fc->s_fs_info = get_net(fc->net_ns);
+	return vfs_get_super(fc, vfs_get_keyed_super, rpc_fill_super);
+}
+
+static void rpc_fs_free_fc(struct fs_context *fc)
 {
-	struct net *net = current->nsproxy->net_ns;
-	return mount_ns(fs_type, flags, data, net, net->user_ns, rpc_fill_super);
+	if (fc->s_fs_info)
+		put_net(fc->s_fs_info);
+}
+
+static const struct fs_context_operations rpc_fs_context_ops = {
+	.free		= rpc_fs_free_fc,
+	.get_tree	= rpc_fs_get_tree,
+};
+
+static int rpc_init_fs_context(struct fs_context *fc)
+{
+	put_user_ns(fc->user_ns);
+	fc->user_ns = get_user_ns(fc->net_ns->user_ns);
+	fc->ops = &rpc_fs_context_ops;
+	return 0;
 }
 
 static void rpc_kill_sb(struct super_block *sb)
@@ -1441,7 +1459,7 @@ static void rpc_kill_sb(struct super_block *sb)
 static struct file_system_type rpc_pipe_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "rpc_pipefs",
-	.mount		= rpc_mount,
+	.init_fs_context = rpc_init_fs_context,
 	.kill_sb	= rpc_kill_sb,
 };
 MODULE_ALIAS_FS("rpc_pipefs");