Trying to convert a Linux C project over to C#.

Any idea how to accomplish the following:
Code:

int fd = open("/dev/mem", O_RDWR|O_SYNC);

iostart = mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, DIOBASE);
 

in particular:
opening a device via open();
mapping memory address (DIOBASE) using mmap()
and getpagesize()