Query about UIO

[bill]

At 2011-07-08 02:37:46，"Hans J. Koch" <hjk at hansjkoch.de> wrote:

>On Thu, Jul 07, 2011 at 07:15:25AM -0700, Greg KH wrote:
>> On Thu, Jul 07, 2011 at 03:32:54PM +0800, bill wrote:
>> > Hi, Greg
>> > 
>> > I've been reading the UIO code, one place puzzled me a lot.
>> > May I ask one question about it?
>> > 
>> > -------------------------------------------------------------------------------
>> > drivers/uio/uio.c
>> > static int uio_find_mem_index(struct vm_area_struct *vma)
>> > {
>> >     int mi;
>> >     struct uio_device *idev = vma->vm_private_data;
>> > 
>> >     for (mi = 0; mi < MAX_UIO_MAPS; mi++) {
>> >         if (idev->info->mem[mi].size == 0)
>> >             return -1;
>> >         if (vma->vm_pgoff == mi)
>> >             return mi;
>> >     }
>> >     return -1;
>> > }
>> > 
>> > I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS],
>> > Suppose there are twohardware memory space, if user intends to map the 2nd mem, then
>> > the last parameter of mmap should be 1,
>> > 
>> > mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED,
>> >                fd, 1);
>> > 
>> > Is my understanding correct?
>
>No, it isn't. The last parameter of mmap is divided by PAGE_SIZE before it
>reaches the UIO core. Therefore, it has to be set to n * getpagesize().
>This is explained in the docs under Documentation/DocBook/.
>Use "make htmldocs" to generate HTML documentation. A faster way is to do
>
>dblatex Documentation/DocBook/uio-howto.tmpl
>
>This generates a PDF with the UIO documentation, provided you have a working
>LaTeX system, and have dblatex installed.
>
>Thanks,
>Hans
>
Thanks for your explanation.
So vma->vm_pgoff is not used as its original meanings, that's the point puzzled me.
Now it's clear:)

 >> 
>> I really don't know, sorry.
>> 
>> But Hans should know, Hans?
>> 
>> 
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