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In fact I do not want to consider about user threads, I think they cause some trouble about memory management and I want to leave them for now, I just want to try to implement kernel threads, try getting call for a beginthread like function working in kernel level which creates new threads(does all process initing and other initing of scheduling) in kernel level also I do not want to deal with file system and etc, so I think these functions will be compiled into kernel itself, but I think this is enough for now because kernel does not very often need to call thread except perhaps for some drivers. Certainly I will have to implement priority and other stuff like mutual exclusion, scheduling and process management into this. I think this also makes implementing user threads into os more easily for me in the future. Right? I want to take your ideas on this. I just recently have this in my mind, so there might be some stupid design problem... I will be very happy to hear criticism on my approach to this kernel threading approach... Thanx...

Even if you don't allow user threads straight away, design your code to account for them. It's much easier to design with multithreading in mind from the start than it is to add it afterwards.

So you say that it is better to make design considering user threads and leave holes to fill while implementing?

Yes, exactly right.