Sysfs class attribute problem

Hello all I am new to sysfs interface ans I read about in mochel's documentation. And doing some experiements on it. Let's come to Tue problem, in my module I have a global variable type char* myglobal and it s static, I am putting that value in my one and only class attribute using show function. But for the same if I a user put some value in to the using echo or something, the attribute value is not changing. And one more thing s after I passed the value to the attribute my system not shutting down :( . Please help me how to read values. // in store function I am doing this: Myglobal = bus; Sent from my HTC