problem using xenbus interface

[NAHieu <nahieu@gmail.com>]

Hello,

I a writing a small kernel module for domU, in which I use xenbus and
have some problems:

I use xenbus_scanf to read value of "/restart_mode", but the below
code always failed (got non-zero err)

err = xenbus_scanf("/", "restart_mode", "%s", mode);


Another code like below also failed (I try to make a new node
"/domain/<DOM>/test" with xenbus_mkdir):

err = xenbus_mkdir("/", "test");


I am using the latest xen pulled from -unstable repository. I guess
the problem is I didnt use xenbus interface properly (?) Anybody could
give me some helps?

Thank you a lot,
NAH