EXER1: 给未被映射的地址映射上物理页*

/* do_pgfault - interrupt handler to process the page fault execption
 * @mm         : the control struct for a set of vma using the same PDT 缺页异常的进程对应的 mm
 * @error_code : the error code recorded in trapframe->tf_err which is setted by x86 hardware
 * @addr       : the addr which causes a memory access exception, (the contents of the CR2 register)
 *
 * CALL GRAPH: trap--> trap_dispatch-->pgfault_handler-->do_pgfault
 */
int
do_pgfault(struct mm_struct *mm, uint32_t error_code, uintptr_t addr) {
    int ret = -E_INVAL;
    // 根据 addr 参数找到对应的 vma 结构
    struct vma_struct *vma = find_vma(mm, addr);

    pgfault_num++;
    // 未找到有效的 vma
    if (vma == NULL || vma->vm_start > addr) {
        cprintf("not valid addr %x, and  can not find it in vma\n", addr);
        goto failed;
    }
    // 根据 error_code 判断错误类型
    switch (error_code & 3) {
    default:
            /* error code flag : default is 3 ( W/R=1, P=1): write, present */
    case 2: /* error code flag : (W/R=1, P=0): write, not present */
        if (!(vma->vm_flags & VM_WRITE)) {
            cprintf("do_pgfault failed: error code flag = write AND not present, but the addr's vma cannot write\n");
            goto failed;
        }
        break;
    case 1: /* error code flag : (W/R=0, P=1): read, present */
        cprintf("do_pgfault failed: error code flag = read AND present\n");
        goto failed;
    case 0: /* error code flag : (W/R=0, P=0): read, not present */
        if (!(vma->vm_flags & (VM_READ | VM_EXEC))) {
            cprintf("do_pgfault failed: error code flag = read AND not present, but the addr's vma cannot read or exec\n");
            goto failed;
        }
    }
    /* IF (write an existed addr ) OR
     *    (write an non_existed addr && addr is writable) OR
     *    (read  an non_existed addr && addr is readable)
     * THEN
     *    continue process
     */
    uint32_t perm = PTE_U;
    // 读写属性
    if (vma->vm_flags & VM_WRITE) {
        perm |= PTE_W;
    }
    addr = ROUNDDOWN(addr, PGSIZE); // 页对齐

    ret = -E_NO_MEM; // 如果再出错，则是内存不足

    pte_t *ptep=NULL;
    /*LAB3 EXERCISE 1: YOUR CODE
    *
    * MACROs or Functions:
    *   get_pte : lab2 中实现的函数，通过 la 获取页表项，若不存在则创建一个
    *   pgdir_alloc_page : 调用 alloc_page 和 page_insert 函数分配页，建立 pa 和 la 的映射添加到页表
    *
    * DEFINES:
    *   VM_WRITE  : If vma->vm_flags & VM_WRITE == 1/0, then the vma is writable/non writable
    *   PTE_W           0x002                   // page table/directory entry flags bit : Writeable
    *   PTE_U           0x004                   // page table/directory entry flags bit : User can access
    * VARIABLES:
    *   mm->pgdir : the PDT of these vma
    *
    */
#if 0
    /*LAB3 EXERCISE 1: YOUR CODE*/
    ptep = ???              //(1) try to find a pte, if pte's PT(Page Table) isn't existed, then create a PT.
    if (*ptep == 0) {
                            //(2) if the phy addr isn't exist, then alloc a page & map the phy addr with logical addr

    }
    else {
    /*LAB3 EXERCISE 2: YOUR CODE
    * 当页存在于 swap 分区时，要根据 PTE 将页换入
    *
    *  MACROs or Functions:
    *    swap_in(mm, addr, &page) : alloc a memory page, then according to the swap entry in PTE for addr,
    *                               find the addr of disk page, read the content of disk page into this memroy page
    *    page_insert ： build the map of phy addr of an Page with the linear addr la
    *    swap_map_swappable ： set the page swappable
    */
        if(swap_init_ok) {
            struct Page *page=NULL;
                                    //(1）According to the mm AND addr, try to load the content of right disk page
                                    //    into the memory which page managed.
                                    //(2) According to the mm, addr AND page, setup the map of phy addr <---> logical addr
                                    //(3) make the page swappable.
        }
        else {
            cprintf("no swap_init_ok but ptep is %x, failed\n",*ptep);
            goto failed;
        }
   }
#endif
    if((ptep = get_pte(mm->pgdir, addr, 1)) == NULL) {
        cprintf("get_pte in do_pgfault failed\n");
        goto failed;
    }
    // 页表项为 0 表示没有与物理页面建立映射关系，pgdir_alloc_page 函数分配了一个页帧
    if(*ptep == 0) {
        if (pgdir_alloc_page(mm->pgdir, addr, perm) == NULL) {
            cprintf("pgdir_alloc_page in do_pgfault failed\n");
            goto failed;
        }
    }
    // 要处理的另一种情况，就是页存在于 swap 分区
    else {
        if(swap_init_ok) {
            struct Page *page = NULL;
            // 换入操作
            if ((ret = swap_in(mm, addr, &page)) != 0) {
                cprintf("swap_in in do_pgfault failed\n");
                goto failed;
            }
            page_insert(mm->pgdir, page, addr, perm); // 设置页表项
            swap_map_swappable(mm, addr, page, 1);    // 设置页可交换
            page->pra_vaddr = addr;                   // 设置页对应的虚拟地址
        }
        else {
            cprintf("no swap_init_ok but ptep is %x, failed\n",*ptep);
            goto failed;
        }
    }
    ret = 0;
failed:
    return ret;
}

// pgdir_alloc_page
// 分配一个页并且设置 la 与 pa 的映射关系
struct Page *
pgdir_alloc_page(pde_t *pgdir, uintptr_t la, uint32_t perm) {
    struct Page *page = alloc_page(); // 分配一个页
    if (page != NULL) {
        // page_insert 通过 la 找到 ptep 地址并设置值
        if (page_insert(pgdir, page, la, perm) != 0) {
            free_page(page);
            return NULL;
        }
        if (swap_init_ok){
            // 实现页换入换出
            swap_map_swappable(check_mm_struct, la, page, 0);
            page->pra_vaddr=la;
            assert(page_ref(page) == 1);
        }

    }

    return page;
}