about userlevel and kernel level

[Eddie Kohler]

> Maybe this is quite simple, but would any of you
> kindly tell me the difference between userlevel and
> kernel level. In the userlevel, can I build extra
> elements? How do you choose to use user level and
> kernel level?

The two drivers are different in that they run at different places -- at
user level or in the kernel. These environments impose different
constraints and support different functionality. For example, you can't
implement device polling at user level, but you can't link with C++
standard libraries or make system calls in the kernel. Also, user level is
easier to debug. There are elements that build only at user level, and
elements that build only for the kernel, but most elements compile
perfectly well for either.

Eddie