Question

您好，

我正在尝试编写一个用户程序来打印'mem_map'数组中所有页面的'flags'字段的值。然后我想看看是否设置了保留位。

对于初学者，我编写了一个内核模块来打印'mem_map'数组中前20页的值，它们各自的'flags'字段和PageReserved宏的输出。

for (;i < 20; ++i) {
  unsigned long *value = &(mem_map[i].flags);
  printk("i = %u page->flags value = %u phy address = %#x isReserved = %d\n", i,mem_map[i].flags, virt_to_phys(&(mem_map[i].flags)),PageReserved(&mem_map[i]));
}

当我运行“dmesg | tail -50”时，我看到以下值：

[ 2858.387520] i = 0 page->flags value = 0    phy address = 0x36840000 isReserved = 0
[ 2858.387520] i = 1 page->flags value = 1024 phy address = 0x36840020 isReserved = 1
[ 2858.387520] i = 2 page->flags value = 1024 phy address = 0x36840040 isReserved = 1
[ 2858.387520] i = 3 page->flags value = 1024 phy address = 0x36840060 isReserved = 1

请注意，我正在打印'flags'字段的物理地址以及值。

我想通过指针查看地址，在用户程序中重现上述结果。

我打开'/ dev / mem'，第一页'flag'字段的偏移量为：0x36840000。我确保在关闭STRICT_DEVMEM的情况下编译内核，并在'devmem_is_allowed（）'函数中添加了默认的'return 1'。

 /* create the offset for mmap() using the physical address of the
    mem_map[] array*/
    off_t offset = 0x36840000;

    /* /dev/mem contains the physical memory map */
    if ((fd = open("/dev/mem", O_RDONLY)) == -1) {
        printf("/dev/mem could not be opened.\n");
        perror("open");
        exit(1);
    else {
        printf("/dev/mem opened.\n");
    }

    starting_page = (char*)mmap(0, MAP_SIZE, PROT_READ,MAP_SHARED, fd,offset);

    if (starting_page == MAP_FAILED) {
        perror("mmap");
        return -1;
    } 
    else {
        printf("Memory mapped at address %p.\n", starting_page);
    }
    mapped_page = starting_page;
    for (i=0;i<10;++i,mapped_page+=32) { 
        printf("\npage i = %u flags value %ul  ", i, *(mapped_page));
    }

但是，当我只打印出“标志值”的值时，我得到零。关于我得到什么零以及如何调试它的任何建议？

谢谢！ -RR

如何在基于Linux的用户程序中的'struct page'中打印'flags'字段

0 个答案: