+/**
+ * lookup_one - filesystem helper to lookup single pathname component
+ * @mnt_userns: user namespace of the mount the lookup is performed from
+ * @name: pathname component to lookup
+ * @base: base directory to lookup from
+ * @len: maximum length @len should be interpreted to
+ *
+ * Note that this routine is purely a helper for filesystem usage and should
+ * not be called by generic code.
+ *
+ * The caller must hold base->i_mutex.
+ */
+struct dentry *lookup_one(struct user_namespace *mnt_userns, const char *name,
+ struct dentry *base, int len)
+{
+ struct dentry *dentry;
+ struct qstr this;
+ int err;
+
+ WARN_ON_ONCE(!inode_is_locked(base->d_inode));
+
+ err = lookup_one_common(mnt_userns, name, base, len, &this);
+ if (err)
+ return ERR_PTR(err);
+
+ dentry = lookup_dcache(&this, base, 0);
+ return dentry ? dentry : __lookup_slow(&this, base, 0);
+}
+EXPORT_SYMBOL(lookup_one);
+