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    SubjectRe: Calculating kernel logical address ..
    On Monday 09 September 2002 20:08, Andrew Morton wrote:
    > Imran Badr wrote:
    > >
    > > The virt_to_bus() macro would work only for kernel logical addresses. I am
    > > trying to find a portable way to figure out the kernel logical address of a
    > > user buffer so that I could use virt_to_bus() for DMA. The user address is
    > > mmap'ed from kmalloc'ed buffer in the mmap() entry of my driver. Now when
    > > the user wants to send this data to the PCI device, it makes an ioctl call
    > > and give the user address to the driver. Now driver has to figure out the
    > > kernel logical address for DMA.
    > You can obtain this info by walking the user's pagetables with
    > get_user_pages(). That give `struct page' pointers, with which
    > all things are possible.

    As long as you can be sure they won't spontaneously vanish on you.

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