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    SubjectRE: locking user memory and kiobuf
    Jeff Garzik [] wrote:
    > "Tony E. Bennett" wrote:
    > > kiobuf sounds perfect for a problem we have. Currently I
    > use mmap() to map
    > > pages from __get_free_pages() into user space for dma.
    > This is not totally
    > > satisfactory, tho, in part because the resulting group of
    > pages is not mapped
    > > contiguously into kernel.
    > This is a question I still have unanswered: Does
    > map_user_kiobuf indeed
    > map the VM into a _contiguous_ region of physical memory?

    I don't think so. There is nothing in there I see that would indicate it

    It just calls handle_mm_fault() to bring in the necessary pages. See
    map_user_kiobuf() in the mm/memory.c source file.

    For me, this isn't a problem. I've got scatter/gather DMA capability.

    > Note struct kiobuf includes an array of pages which causes some of my
    > confusion. Is it legal/possible to do:
    > /* maps in four pages for read/write access */
    > err = map_user_kiobuf (WRITE, iobuf, (ulong) vmaddr,
    > PAGE_SIZE * 4);
    > /* manipulate data in chunks greater than PAGE_SIZE */
    > phys = page_address(iobuf->maplist[0]);
    > memcpy (foo, phys, PAGE_SIZE * 4);

    The pages should be virtually contiguous in user space, so I think something
    like this my work.

    Does page_address() return a virtual or physical address? To me it looks
    like it may be a physical address, in which case you would have to do:
    memcpy (foo, phys_to_virt(phys), PAGE_SIZE *4);


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