Interfacing functions between user space and kernel space

•       The kernel offers several subroutines or functions in user space, which allow the end-user application programmer to interact with the hardware. Usually, in UNIX or Linux systems, this dialogue is performed through functions or subroutines in order to read and write files. The reason for this is that in Unix/Linux devices are seen, from the point of view of the user, as files.

•       On the other hand, in kernel space Linux also offers several functions or subroutines to perform the low level interactions directly with the hardware, and allow the transfer of information from kernel to user space.

•       Usually, for each function in user space (allowing the use of devices or files), there exists an equivalent in kernel space (allowing the transfer of information from the kernel to the user and vice-versa).