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SubjectRe: DMA from SCSI controller to PCI frame buffer memory.
Alan Cox wrote:
>
> On Fri, 2002-12-13 at 19:15, Jason Howard wrote:
> > Hello All,
> >
> > I am wondering if the functionality exists in the Linux kernel to DMA
> > from a SCSI controller directly into frame buffer memory of a PCI video
> > card? Is there a standard method for this (similar to sendfile) or will
> > it require some hacking?
>
> In theory you can mmap the frame buffer memory, then do O_DIRECT I/O
> into it. In practice it will buffer (I hope it still does).

An O_DIRECT disk read into a mmapped device region will fail (if
it doesn't, it'll oops ;)). O_DIRECT requires valid pages inside
mem_map[].

See the `vma->vm_flags & VM_IO' test in get_user_pages(), and
the VALID_PAGE() test in get_page_map().

Hacking is required to do this.
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