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dev/kmem和dev/mem的区别在于dev/kmem 只能mmap kernel的low memory,而/dev/mem 可以映射4G范围内的memory dev/kmem的mmap实现如下: 其中最重要的一行是360行的虚拟地址转物理地址。是通过直接减去offset来完成的,而只有kernel的low memory才可以这么计算.计算完之后,在373行调用和/dev/mem一样的函数来做映射. 355 static int mmap_kmem(struct file *file, struct vm_area_struct *vma) 356 { 357 unsigned long pfn; 358 359 /* Turn a kernel-virtual address into a physical page frame */ 360 pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT; 361 362 /* 363 * RED-PEN: on some architectures there is more mapped memory than 364 * available in mem_map which pfn_valid checks for. Perhaps should add a 365 * new macro here. 366 * 367 * RED-PEN: vmalloc is not supported right now. 368 */ 369 if (!pfn_valid(pfn)) 370 return -EIO; 371 372 vma->vm_pgoff = pfn; 373 return mmap_mem(file, vma); 374 }转载地址:http://ovcmi.baihongyu.com/