操作系统课程设计Record

用户程序：

#include <stdio.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h> /* open */
#include <stdint.h> /* uint64_t  */
#include <stdlib.h> /* size_t */
#include <unistd.h> /* pread, sysconf */

typedef struct {
    uint64_t pfn : 54;
    unsigned int soft_dirty : 1;
    unsigned int file_page : 1;
    unsigned int swapped : 1;
    unsigned int present : 1;
} PagemapEntry;


int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr)
{
    size_t nread;
    ssize_t ret;
    uint64_t data;
    uintptr_t vpn;

    vpn = vaddr / sysconf(_SC_PAGE_SIZE);
    nread = 0;
    while (nread < sizeof(data)) {
        ret = pread(pagemap_fd, &data, sizeof(data) - nread,
                vpn * sizeof(data) + nread);
        nread += ret;
        if (ret <= 0) {
            return 1;
        }
    }
    entry->pfn = data & (((uint64_t)1 << 54) - 1);
    entry->soft_dirty = (data >> 54) & 1;
    entry->file_page = (data >> 61) & 1;
    entry->swapped = (data >> 62) & 1;
    entry->present = (data >> 63) & 1;
    return 0;
}
int virt_to_phys_user(uintptr_t *paddr, pid_t pid, uintptr_t vaddr)
{
    char pagemap_file[BUFSIZ];
    int pagemap_fd;

    //读取对应进程地址映射
    snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid);
    pagemap_fd = open(pagemap_file, O_RDONLY);
    if (pagemap_fd < 0) {
        return 1;
    }
    PagemapEntry entry;
    //条目获取
    if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) {
        return 1;
    }
    close(pagemap_fd);
    *paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE));
    return 0;
}

int main(void) {
    setbuf(stdout, 0);
    int a = 0;
    pid_t pid = fork();
    if (pid == 0) 
    {
    	  //子进程
    	  printf("Pid:%d\n",getpid());
          printf("child: \n\tvirtual address:\t%llx\n\tphysical address:\t%llx\n", &a, syscall(335, &a));
          sleep(2);
    }
    else
    {
    	//父进程
    	printf("Pid:%d\n",getpid());
    	printf("parent: \n\tvirtual address:\t%llx\n\tphysical address:\t%llx\n", &a, syscall(335, &a));
    	uintptr_t aptr = &a;
        uintptr_t aphy = NULL;
        //子进程中该变量的物理地址
        virt_to_phys_user(&aphy, pid, aptr);
        printf("child:\n\tpagemap approach:\t%llx\n", aphy);
    	sleep(2);
    }
    return 0;
}

系统调用：

#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <asm/current.h>
#include <asm/pgtable_types.h>

SYSCALL_DEFINE1(phy_addr_at, unsigned long, addr) {
    resource_size_t res = 0;
    pte_t *pte;
    spinlock_t *ptlp;

    if (current->mm == NULL) {
          printk("error: current process is anonymous.");
          return -1;
    }
    
  	/**
     * 通过mm_struct获取pgd，即第一级页表，然后根据addr逐级深入，
     * 最终获得pte，即第四级页表（page table entries）的页表项，
     * 注意这个过程需要锁ptlp
     */
    follow_pte(current->mm, (unsigned long)addr, &pte, &ptlp);

    // 从pte表项中提取pfn，即物理页地址
    unsigned long pfn;
    pfn = pte->pte;
    pfn ^= (pfn && !(pfn & _PAGE_PRESENT)) ? ~0ull : 0;
    pfn = (pfn & PTE_PFN_MASK) >> PAGE_SHIFT;
    
    // 由物理页地址以及当前虚拟页偏移得到实际物理地址
    res = (pfn << PAGE_SHIFT) | (addr & ~(~0 << PAGE_SHIFT));
  
    // 注意释放资源
    pte_unmap_unlock(pte, ptlp);
    
    return (unsigned long long)res;
}

参考M4tsuri师傅的作业（加个系统调用在别的学校是小作业，在我这就是课程设计了......）。

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