I tried rapidxen once.
They provided a web-based ajax terminal webpage, which displays tty0 on the webpage and you can type command on that webpage. It interactive with domU in ajax way, the webpage sends POST request every few seconds to a URL ended with "ajaxConsoleProxy", a little like "KVM over IP"
Is there any opensource project which can do the same thing?
UPDATE: I tried AjaxTerm, but it needs to be run on every domU. Is there any better solution? Can I just install some program on dom0 and then use it to connect to domU?
UPDATE AGAIN: I figured out myself. Please read the answer below.