open-style analog of vfs_path_lookup()

new function: file_open_root(dentry, mnt, name, flags) opens the file
vfs_path_lookup would arrive to.

Note that name can be empty; in that case the usual requirement that
dentry should be a directory is lifted.

open-coded equivalents switched to it, may_open() got down exactly
one caller and became static.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfsctl.c b/fs/nfsctl.c
index bf9cbd2..124e8fc 100644
--- a/fs/nfsctl.c
+++ b/fs/nfsctl.c
@@ -22,30 +22,17 @@
 
 static struct file *do_open(char *name, int flags)
 {
-	struct nameidata nd;
 	struct vfsmount *mnt;
-	int error;
+	struct file *file;
 
 	mnt = do_kern_mount("nfsd", 0, "nfsd", NULL);
 	if (IS_ERR(mnt))
 		return (struct file *)mnt;
 
-	error = vfs_path_lookup(mnt->mnt_root, mnt, name, 0, &nd);
+	file = file_open_root(mnt->mnt_root, mnt, name, flags);
+
 	mntput(mnt);	/* drop do_kern_mount reference */
-	if (error)
-		return ERR_PTR(error);
-
-	if (flags == O_RDWR)
-		error = may_open(&nd.path, MAY_READ|MAY_WRITE, flags);
-	else
-		error = may_open(&nd.path, MAY_WRITE, flags);
-
-	if (!error)
-		return dentry_open(nd.path.dentry, nd.path.mnt, flags,
-				   current_cred());
-
-	path_put(&nd.path);
-	return ERR_PTR(error);
+	return file;
 }
 
 static struct {