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char * buf;
/* 1. ·­¿ªÎļþ */
 fd = open("/dev/hello", O_RDWR);
 if (fd == -1)
 {
      printf("can not open file /dev/hello\n");
      return -1;
 }

/* 2. mmap
       * MAP_SHARED  : ¶à¸öAPP¶¼Å²ÓÃmmapÓ³Éäͳһ¿éÄÚ´æʱ, ¶ÔÄÚ´æµÄÐ޸ĸ÷È˶¼¿ÉÒÔ¿´µ½¡£
       *               ¾ÍÊÇ˵¶à¸öAPP¡¢Çý¶¯³ÌÐòÏÖʵÉÏ»á¼ûµÄ¶¼ÊÇͳһ¿éÄÚ´æ
       * MAP_PRIVATE : ½¨ÉèÒ»¸öcopy on writeµÄ˽ÓÐÓ³Éä¡£
       *               µ±APP¶Ô¸ÃÄÚ´æ¾ÙÐÐÐÞ¸Äʱ£¬ÆäËû³ÌÐòÊÇ¿´²»µ½ÕâЩÐ޸ĵÄ¡£
       *               ¾ÍÊǵ±APPдÄÚ´æʱ, Äں˻áÏȽ¨ÉèÒ»¸ö¿½±´¸øÕâ¸öAPP,
       *               Õâ¸ö¿½±´ÊÇÕâ¸öAPP˽ÓеÄ, ÆäËûAPP¡¢Çý¶¯ÎÞ·¨»á¼û¡£
       */
buf =  mmap(NULL, 1024*8, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

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µÚÈý¸ö²ÎÊýPROT_READ | PROT_WRITEÌåÏÖÓ³ÉäºóµÄ¿Õ¼äÊǿɶÁ¿ÉдµÄ¡£

µÚËĸö²ÎÊý¿ÉÌîMAP_SHARED»òMAP_PRIVATE£º

MAP_SHARED£º¶à¸öAPP¶¼Å²ÓÃmmapÓ³Éäͳһ¿éÄÚ´æʱ, ¶ÔÄÚ´æµÄÐ޸ĸ÷È˶¼¿ÉÒÔ¿´µ½¡£¾ÍÊÇ˵¶à¸öAPP¡¢Çý¶¯³ÌÐòÏÖʵÉÏ »á¼ûµÄ¶¼ÊÇͳһ¿éÄÚ´æ¡£

MAP_PRIVATE£º½¨ÉèÒ»¸öcopy on writeµÄ˽ÓÐÓ³Éä¡£µ±APP¶Ô¸ÃÄÚ´æ¾ÙÐÐÐÞ¸Äʱ£¬ÆäËû³ÌÐòÊÇ¿´²»µ½ÕâЩÐ޸ĵÄ¡£¾ÍÊǵ±APP дÄÚ´æʱ, Äں˻áÏȽ¨ÉèÒ»¸ö¿½±´¸øÕâ¸öAPP£¬Õâ¸ö¿½±´ÊÇÕâ¸öAPP˽ÓеÄ, ÆäËûAPP¡¢Çý¶¯ÎÞ·¨»á¼û¡£

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int remap_pfn_range(
  struct vm_area_struct *vma, 
  unsigned long addr, 
  unsigned long pfn, 
  unsigned long size, 
  pgprot_t prot);

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vma£ºÐÎòһƬӳÉäÇøÓòµÄ½á¹¹ÌåÖ¸Õë

addr£ºÒªÓ³ÉäµÄÐéÄâµØµãÆðʼµØµã

pfn£ºÎïÀíÄÚ´æËù¶ÔÓ¦µÄÒ³¿òºÅ£¬¾ÍÊǽ«ÎïÀíµØµã³ýÒÔÒ³¾Þϸ»ñµÃµÄÖµ

size£ºÓ³ÉäµÄ¾Þϸ

prot£º¸ÃÄÚ´æÇøÓòµÄ»á¼ûȨÏÞ

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1¡¢Ê¹ÓÃkmalloc»òÕßkzallocº¯Êý·ÖÅÉÒ»¿éÄÚ´ækernel_buf£¬ÓÉÓÚÕâÑù·ÖÅɵÄÄÚ´æÎïÀíµØµãÊÇÒ»Á¬µÄ£¬mmapºóÓ¦Óòã»á¶ÔÕâÒ»¸ö»ùµØµãÈ¥»á¼ûÕâ¿éÄÚ´æ¡£

2¡¢ÊµÏÖmmapº¯Êý

static int hello_drv_mmap(struct file *file, struct vm_area_struct *vma)
{
 /* »ñµÃÎïÀíµØµã */
 unsigned long phy = virt_to_phys(kernel_buf);//kernel_bufÊÇÄں˿ռä·ÖÅɵÄÒ»¿éÐéÄâµØµã¿Õ¼ä
    
    /* ÉèÖÃÊôÐÔ£ºcache, buffer*/
 vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
    
    /* map */
    if(remap_pfn_range(vma, vma->vm_start, phy>>PAGE_SHFIT,
                      vma->vm_end - vma->start, vma->vm_page_prot)){
 printk("mmap remap_pfn_range failed\n");
    return -ENOBUFS;
 }
 return 0;
}

static struct file_operations my_fops = {
 .mmap = hello_drv_mmap,
};

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1¡¢Í¨¹ývirt_to_phys½«ÐéÄâµØµãתΪÎïÀíµØµã£¬ÕâÀïµÄkernel_bufÊÇÄں˿ռäµÄÒ»¿éÐéÄâµØµã¿Õ¼ä

2¡¢ÉèÖÃÊôÐÔ£º²»Ê¹ÓÃcache£¬Ê¹ÓÃbuffer

3¡¢Ó³É䣺ͨ¹ýremap_pfn_rangeº¯ÊýÓ³É䣬phy>>PAGE_SHIFT×Åʵ¾ÍÊÇ°´pageÓ³É䣬³ýÁËÕâ¸ö²ÎÊý£¬ÆäËûµÄÆðʼµØµã¡¢¾ÞϸºÍȨÏÞ¶¼¿ÉÒÔÓÉÓû§ÔÚϵͳŲÓú¯ÊýÖÐÖ¸¶¨¡£

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