read_mmap

read_mmap:

	/* Atomically increment the reference counter, 
            * so no one unmaps the buffer while we use it. */
	atomic_add(mmap_use_count, 1);

	/* If the buffer is being resized, use the system call instead of the mapped buffer. */
	if (mmap_resizing)
		atomic_decr(mmap_use_count, 1);
		read_syscall(...);
	else
		memcpy(dst_buffer, mapped_buffer, …);
		atomic_decr(mmap_use_count, 1);