[readdir] introduce iterate_dir() and dir_context

iterate_dir(): new helper, replacing vfs_readdir().

struct dir_context: contains the readdir callback (and will get more stuff
in it), embedded into whatever data that callback wants to deal with;
eventually, we'll be passing it to ->readdir() replacement instead of
(data,filldir) pair.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 4e9a21d..4f8cc6b 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -263,7 +263,10 @@
 {
 	const struct cred *original_cred;
 	struct dentry *dir = nn->rec_file->f_path.dentry;
-	LIST_HEAD(names);
+	struct {
+		struct dir_context ctx;
+		struct list_head names;
+	} ctx;
 	int status;
 
 	status = nfs4_save_creds(&original_cred);
@@ -276,11 +279,13 @@
 		return status;
 	}
 
-	status = vfs_readdir(nn->rec_file, nfsd4_build_namelist, &names);
+	INIT_LIST_HEAD(&ctx.names);	
+	ctx.ctx.actor = nfsd4_build_namelist;
+	status = iterate_dir(nn->rec_file, &ctx.ctx);
 	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
-	while (!list_empty(&names)) {
+	while (!list_empty(&ctx.names)) {
 		struct name_list *entry;
-		entry = list_entry(names.next, struct name_list, list);
+		entry = list_entry(ctx.names.next, struct name_list, list);
 		if (!status) {
 			struct dentry *dentry;
 			dentry = lookup_one_len(entry->name, dir, HEXDIR_LEN-1);