User space memory

[Prabhu nath]

On Sun, Mar 10, 2013 at 11:30 PM, Christoph Seitz <c.seitz at tu-bs.de> wrote:

> Hi all,
>
> I have some problems allocation Memory the right way and use it in my
> kernel module.
>
> I use a char device for reading and writing from/to a pcie dma card.
> Especially the read function makes me some headache. The user allocates
> some memory with posix_memalign and call the read function on the
> device, so that the devices knows where to write to. My driver now uses
> get_user_pages() to pin the user pages. The memory has never been
> written or read by the user, so it's not yet in the RAM, right? And
> get_user_pages returns a valid number of pages, but for every page the
> same struct. (respectively the same pointer). Is there any way to ensure
> that the user pages are in the ram and get_user_pages returns a valid
> page array?
>

If you know the RAM physical address range you can figure out by doing the
following
    *page_to_pfn(page_ptr) << 12*;
    where page_ptr is a struct page * returned by get_user_pages().
   * page_to_pfn()* will return the pfn of the corresponding page frame and
left shifting by 12 bits will give you page frame base address.



> Regards
> Chris
>
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-- 
Regards,
Prabhunath G
Linux Trainer
Bangalore
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