On Thu, 2003-05-15 at 20:32, Andrew Morton wrote:
> "Rick Smith" <rgsmith72@xxxxxxxxxxx> wrote:
> >
> > What are the memory address restrictions when using the O_DIRECT flag
> > with XFS? I am trying to perform I/O directly from the filesystem to a
> > piece
> > of mmap'ed video memory and I get the "bad address" error when I attempt to
> > do so with O_DIRECT.
>
> It cannot be done - O_DIRECT only supports IO against legitimate RAM
> (memory which is described by the pageframes in mem_map[]).
You mean it cannot be done with the infrastructure we have now, but
it would be a cool thing to do. In fact there are legitimate
applications for this. I know we have folks who move textures
direct from disk to video devices on Irix - they want a lot more
textures than they have memory.
Most of the reason for the infrastructure in place at the moment is
to keep the memory in one place while the dma happens. If that
is guaranteed in some other way, then it would be possible, just
a matter of getting the addresses down to the drivers.
Probably a lot of work though.
Steve
--
Steve Lord voice: +1-651-683-3511
Principal Engineer, Filesystem Software email: lord@xxxxxxx
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