Re: [PATCH RFCv2 1/3] fs: introduce helper d_path_fast()

On Fri, May 28, 2021 at 07:39:49PM +0800, Jia He wrote:

+/**
+ * d_path_fast - fast return the full path of a dentry without taking
+ * any seqlock/spinlock. This helper is typical for debugging purpose
+ */
+char *d_path_fast(const struct path *path, char *buf, int buflen)
+{
+	struct path root;
+	struct mount *mnt = real_mount(path->mnt);
+	DECLARE_BUFFER(b, buf, buflen);
+
+	rcu_read_lock();
+	get_fs_root_rcu(current->fs, &root);
+
+	prepend(&b, "", 1);
+	__prepend_path(path->dentry, mnt, &root, &b);
+	rcu_read_unlock();
+
+	return extract_string(&b);
+}
+EXPORT_SYMBOL(d_path_fast);

Umm...  I'd suggest failing if __prepend_path() returns 3 (at least)...