Alan, On Wed, Oct 23, 2002 at 01:40:09AM +0100, Jos� Fonseca wrote:
Ok. I've already have a simple C routine which copies and verifies theOn Wed, Oct 23, 2002 at 01:01:39AM +0100, Alan Cox wrote:... I would expect to want to prefetch the input data (please trust copy_from_user to do this right, it doesn't do a good job yet but its the business of that code to do it). ...But if I call copy_from_user I won't be making the copy and verify in one pass, as advised below. Should I adapt copy_from_user to do that then? ...
buffers. It's now reading from a DMA buffer which is mmap'd on userspace
but I want it to read directly from the userspace as there is no point
in wasting DMA memory on clients if no DMA operation will be made on
from it.
I've studied the current implementation of copy_from_user. For those
interested (not you, of course! :), the relevant bits are in
include/asm-i386/uaccess.h and
http://kernelnewbies.org/documents/copy_user/ . But although I do
understand the assembly implementation and I actually plan to do an
assembly optimized version myself, I would like to start with a plain C
implementation that would be platform independent.
But it doesn't seem I can get away of assembly due to the exception
table. So the only way is to do it portably is to call __copy_user
inside my routine for every read, or do you have any other suggestion
you can give me?
Thanks in advance,
Jos� Fonseca
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