EXER2: 父进程复制自己的内存空间给子进程*

/* copy_range - copy content of memory (start, end) of one process A to another process B
 * @to:    the addr of process B's Page Directory
 * @from:  the addr of process A's Page Directory
 * @share: flags to indicate to dup OR share. We just use dup method, so it didn't be used.
 *
 * CALL GRAPH: copy_mm-->dup_mmap-->copy_range
 */
int
copy_range(pde_t *to, pde_t *from, uintptr_t start, uintptr_t end, bool share) {
    ...
        /* LAB5:EXERCISE2 YOUR CODE
         * replicate content of page to npage, build the map of phy addr of nage with the linear addr start
         *
         * MACROs or Functions:
         *    page2kva(struct Page *page): return the kernel vritual addr of memory which page managed (SEE pmm.h)
         *    page_insert: build the map of phy addr of an Page with the linear addr la
         *    memcpy: typical memory copy function
         *
         * (1) find src_kvaddr: the kernel virtual address of page
         * (2) find dst_kvaddr: the kernel virtual address of npage
         * (3) memory copy from src_kvaddr to dst_kvaddr, size is PGSIZE
         * (4) build the map of phy addr of  nage with the linear addr start
         */
        void *p_kva = page2kva(page);
        void *np_kva = page2kva(npage);
        memcpy(np_kva, p_kva, PGSIZE);
        ret = page_insert(to, npage, start, perm);
    ...
}