Linux Zero Copy

Question

I have a PCI device that needs to read and write from userspace. I'm trying to use zero copy; is there a way to allocate, pin, and get the physical address of a userspace address completely within userspace or do I need to have a kernel module that, say, calls virt_to_phys or get_user_pages? The device's memory is mapped into userspace memory via MMIO so I can pass it any data that's needed. Thanks.

Answer 1

It was a total hack, but I limited Linux to a range of memory and used MMIO to allocate memory for my device that the kernel was unaware of.

Answer 2

Basically you need the memory to be DMA-able, and as far as I know only a kernel module can do that. See http://lxr.free-electrons.com/source/Documentation/PCI/PCI-DMA-mapping.txt