how to access user space memory from kernel.

[David Sanán Baena]

Hi. I need to access to user space memory from a kernel module. This module
is not a driver, so I would like how can i write and read from/to a variable
in a user application from my kernel module?
At first I thought I could do that with shared memory (shmget, shmat...),
but in that is not possible in a kernel module. So I have thought to do it
with copy_from_user and copy_to_user, but i don't know how to do it exactly,
basically how to know where to write or read in the user var...
Any suggestion???
Thanks in advance