Remap_pfn_range, Vm_pgoff, PFN

Http://linux.chinaunix.net/bbs/archiver/tid-900802-page-2.html
Http://www.linuxforum.net/forum/showflat.php? cat=&board=linuxk&number=651015&page=0&view=collapsed&sb=5&o=7&fpart=

1. Vma->vm_pgoff is the offset of the VM area in the page size in map file. /* Offset (within vm_file) in page_size*/

For example, 4 Vm_area map to a file
1) 0-----4096
2) 5*4096------7*4096
3) 9*4096------10*4096
4) 15*4096-----20*4096

So the 4 VMA Vm_pgoff were 0,5,9, 15.

It is not related to the physical page number.

and the physical page number you see is a special case and a coincidence.

2, the Remap_pfn_range function is driven by the call (CD drivers grep-r REMAP_PFN *)
Used to " All"Physical memory is mapped into aFile (Driver/mem.c See).

At this point, Vm_pgoff is related to the physical page number. is a special case and a coincidence.
Vm_pgoff's intent is independent of the physical page number.
That's what I'm talking about. (See mm.h Description of a sentence: Offset (within Vm_file) in Page_size)

3. drivers/char/mem.c
static int Mmap_mem (struct file *file, struct vm_area_struct *vma)
{
size_t size = vma->vm_end-vma->vm_start;

if (!valid_mmap_phys_addr_range (vma->vm_pgoff, size))
Return-einval;

if (!PRIVATE_MAPPING_OK (VMA))
Return-enosys;

if (!range_is_allowed (vma->vm_pgoff, size))
Return-eperm;

if (!phys_mem_access_prot_allowed (file, vma->vm_pgoff, size,
&vma->vm_page_prot))
Return-einval;

Vma->vm_page_prot = Phys_mem_access_prot (file, Vma->vm_pgoff,
Size
Vma->vm_page_prot);

vma->vm_ops = &mmap_mem_ops;

/* Remap-pfn-range would mark the range Vm_io and vm_reserved * *
if (Remap_pfn_range (VMA,
Vma->vm_start,
Vma->vm_pgoff,
Size
Vma->vm_page_prot)) {
Return-eagain;
}
return 0;
}

#ifdef CONFIG_DEVKMEM
static int Mmap_kmem (struct file *file, struct vm_area_struct *vma)
{
unsigned long PFN;

/* Turn a kernel-virtual address into a physical page frame * *
PFN = __pa (u64) vma->vm_pgoff << page_shift) >> page_shift;

/*
* Red-pen:on Some architectures there are more mapped memory
* Available in Mem_map which pfn_valid checks for. Perhaps should add a
* New macro here.
*
* Red-pen:vmalloc is isn't supported right now.
*/
if (!pfn_valid (PFN))
Return-eio;

Vma->vm_pgoff = PFN;
return Mmap_mem (file, VMA);
}