DMA to User-Space

[Jonathan Haws]

> > One more question about this approach: does the mmap() call
> prevent
> > the kernel from using this memory for other purposes?  Will the
> > kernel be able to "move" this memory elsewhere?  I guess what I am
> > asking is if this memory is locked for all other purposes?
> 
> You've allocated the memory in the kernel and mapped it to
> userspace.
> If the kernel uses that memory for anything else it will be visible
> to
> userspace.

So, does that mean that the kernel could use that memory for something else?  I was under the impression that locking the memory prevented the kernel from swapping it out, moving it, *and* using it for other purposes.

This memory that I am mapping is reserved for DMA buffers.  If anything else uses it, then that will corrupt my buffer and make it worthless.  So basically I want user space to tell the kernel that that portion of memory is out of bounds.  Is that possible?

Thanks,

Jonathan