Linux内核---62.用户空间获得变量的物理地址

1.  linux内核文档Documentation/vm/pagemap.txt

1.2  用户空间获取物理地址的代码

 cong@msi:/work/test/ctest/vaddr$ cat test.c
 #include <stdio.h>
 #include <unistd.h>
 #include <inttypes.h>
 #include <stdint.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>

 #define page_map_file "/proc/self/pagemap"

 #define PFN_MASK ((((uint64_t)1)<<55)-1)

 #define PFN_PRESENT_FLAG (((uint64_t)1)<<63)

 int mem_addr_vir2phy(unsigned long vir, unsigned long *phy)
 {
     int fd;
     int page_size=getpagesize();
     unsigned long vir_page_idx = vir/page_size;
     unsigned long pfn_item_offset = vir_page_idx*sizeof(uint64_t);
     uint64_t pfn_item;

     fd = open(page_map_file, O_RDONLY);
     if (fd<0)
     {
         printf("open %s failed", page_map_file);
         return -1;
     }
     if ((off_t)-1 == lseek(fd, pfn_item_offset, SEEK_SET))
     {
         printf("lseek %s failed", page_map_file);
         return -1;
     }
     if (sizeof(uint64_t) != read(fd, &pfn_item, sizeof(uint64_t)))
     {
         printf("read %s failed", page_map_file);
         return -1;
     }
     if (0==(pfn_item & PFN_PRESENT_FLAG))
     {
         printf("page is not present");
         return -1;
     }
     *phy = (pfn_item & PFN_MASK)*page_size + vir % page_size;
     return 0;
 }

 void main()
 {
     int a=0x12345678;
     unsigned long phy;
     mem_addr_vir2phy((unsigned long)&a, &phy);
     printf("vaddr=%p,phy=0x%lx\n", &a, phy);
     while(1)
     {
         sleep(100);
     }
 }

注：函数mem_addr_vir2phy代码出自 
《Linux下获取虚拟地址对应的物理地址的方法》
http://www.lai18.com/content/7598292.html
这儿我只是打了一个main函数进行测试

---

二.验证结果的正确性
2.1 使用方法
cong@msi:/work/test/ctest/vaddr/Access_Physical_Memory$ sudo mknod /dev/dram c 85 0

cong@msi:/work/test/ctest/vaddr/Access_Physical_Memory$ ./fileview /dev/dram

注:上述驱动与fileview出自
《Linux用户程序如何访问物理内存》
http://ilinuxkernel.com/?p=1248
2.2.2 我的ubuntun 的内核版本是 3.13.0-49-generic
作了少许改动

 27d26
 < #include <linux/mm.h>
 47,49c46,47
 <     unsigned long pages = get_num_physpages();
 <     //dram_size = (loff_t)num_physpages << PAGE_SHIFT;
 <     dram_size = pages << PAGE_SHIFT;
 ---
 >
 >     dram_size = (loff_t)num_physpages << PAGE_SHIFT;
 77c75
 < #if 1
 ---
 > #if 0

2.3 验证一下结果
2.3.1 这个是用户空间打印出来的物理地址是0x41F47284


2.3.2 这是物理内存0x41F47284处的数据

完全吻合，说明成功
2.4 代码下载
包括fileview和驱动
Access_Physical_Memory.rar(下载后改名为Access_Physical_Memory.tar.bz2)
这个代码出自 http://cs.usfca.edu/~cruse/cs635/

---

附录: 内核文档 Documentation/vm/ pagemap.txt

 pagemap, from the userspace perspective
 ---------------------------------------

 pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow
 userspace programs to examine the page tables and related information by
 reading files in /proc.

 There are three components to pagemap:

  * /proc/pid/pagemap. This file lets a userspace process find out which
    physical frame each virtual page is mapped to. It contains one 64-bit
    value for each virtual page, containing the following data (from
    fs/proc/task_mmu.c, above pagemap_read):

     * Bits 0-54 page frame number (PFN) if present
     * Bits 0-4 swap type if swapped
     * Bits 5-54 swap offset if swapped
     * Bits 55-60 page shift (page size = 1<<page shift)
     * Bit 61 reserved for future use
     * Bit 62 page swapped
     * Bit 63 page present

    If the page is not present but in swap, then the PFN contains an
    encoding of the swap file number and the page's offset into the
    swap. Unmapped pages return a null PFN. This allows determining
    precisely which pages are mapped (or in swap) and comparing mapped
    pages between processes.

    Efficient users of this interface will use /proc/pid/maps to
    determine which areas of memory are actually mapped and llseek to
    skip over unmapped regions.

  * /proc/kpagecount. This file contains a 64-bit count of the number of
    times each page is mapped, indexed by PFN.

  * /proc/kpageflags. This file contains a 64-bit set of flags for each
    page, indexed by PFN.

    The flags are (from fs/proc/page.c, above kpageflags_read):

      0. LOCKED
      1. ERROR
      2. REFERENCED
      3. UPTODATE
      4. DIRTY
      5. LRU
      6. ACTIVE
      7. SLAB
      8. WRITEBACK
      9. RECLAIM
     10. BUDDY
     11. MMAP
     12. ANON
     13. SWAPCACHE
     14. SWAPBACKED
     15. COMPOUND_HEAD
     16. COMPOUND_TAIL
     16. HUGE
     18. UNEVICTABLE
     19. HWPOISON
     20. NOPAGE
     21. KSM

 Short descriptions to the page flags:

  0. LOCKED
     page is being locked for exclusive access, eg. by undergoing read/write IO

  7. SLAB
     page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator
     When compound page is used, SLUB/SLQB will only set this flag on the head
     page; SLOB will not flag it at all.

 10. BUDDY
     a free memory block managed by the buddy system allocator
     The buddy system organizes free memory in blocks of various orders.
     An order N block has 2^N physically contiguous pages, with the BUDDY flag
     set for and _only_ for the first page.

 15. COMPOUND_HEAD
 16. COMPOUND_TAIL
     A compound page with order N consists of 2^N physically contiguous pages.
     A compound page with order 2 takes the form of "HTTT", where H donates its
     head page and T donates its tail page(s). The major consumers of compound
     pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc.
     memory allocators and various device drivers. However in this interface,
     only huge/giga pages are made visible to end users.
 17. HUGE
     this is an integral part of a HugeTLB page

 19. HWPOISON
     hardware detected memory corruption on this page: don't touch the

 20. NOPAGE
     no page frame exists at the requested address

 21. KSM
     identical memory pages dynamically shared between one or more processes

     [IO related page flags]
  1. ERROR IO error occurred
  3. UPTODATE page has up-to-date data
               ie. for file backed page: (in-memory data revision >= on-disk one)
  4. DIRTY page has been written to, hence contains new data
               ie. for file backed page: (in-memory data revision > on-disk one)
  8. WRITEBACK page is being synced to disk

     [LRU related page flags]
  5. LRU page is in one of the LRU lists
  6. ACTIVE page is in the active LRU list
 18. UNEVICTABLE page is in the unevictable (non-)LRU list
                 It is somehow pinned and not a candidate for LRU page reclaims,
         eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments
  2. REFERENCED page has been referenced since last LRU list enqueue/requeue
  9. RECLAIM page will be reclaimed soon after its pageout IO completed
 11. MMAP a memory mapped page
 12. ANON a memory mapped page that is not part of a file
 13. SWAPCACHE page is mapped to swap space, ie. has an associated swap entry
 14. SWAPBACKED page is backed by swap/RAM

 The page-types tool in this directory can be used to query the above flags.

 Using pagemap to do something useful:

 The general procedure for using pagemap to find out about a process' memory
 usage goes like this:

  1. Read /proc/pid/maps to determine which parts of the memory space are
     mapped to what.
  2. Select the maps you are interested in -- all of them, or a particular
     library, or the stack or the heap, etc.
  3. Open /proc/pid/pagemap and seek to the pages you would like to examine.
  4. Read a u64 for each page from pagemap.
  5. Open /proc/kpagecount and/or /proc/kpageflags. For each PFN you just
     read, seek to that entry in the file, and read the data you want.

 For example, to find the "unique set size" (USS), which is the amount of
 memory that a process is using that is not shared with any other process,
 you can go through every map in the process, find the PFNs, look those up
 in kpagecount, and tally up the number of pages that are only referenced
 once.

 Other notes:

 Reading from any of the files will return -EINVAL if you are not starting
 the read on an 8-byte boundary (e.g., if you seeked an odd number of bytes
 into the file), or if the size of the read is not a multiple of 8 bytes.