Demo: Copy a File Using mmap

The third and last variant of the file-copy program. Instead of reading into a buffer and writing back out, this one asks the kernel to map both files directly into the process address space, so that copying the file becomes a single memcpy() between two pointers — and the read/write loop disappears entirely.

Together with the teaching assistant you will fill in the TODOs in copy_file.c, then build and verify the copy. Along the way you will meet ftruncate(), msync() and munmap(), and see that the actual I/O happens through page faults rather than through any call you wrote.