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SubjectRe: Calculating kernel logical address ..
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.
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