Re: [PATCH 2.6.25] module: allow ndiswrapper to use GPL-only symbols

Pavel Roskin
2008-03-04T05:37:33Z

Quoting Ingo Molnar <mingo@elte.hu>:

>
> * Pavel Roskin <proski@gnu.org> wrote:
>
>> > btw., what are the technical reasons why ndiswrapper cannot be done
>> > in userspace, much like the (wildly successful) FUSE concept?
>>
>> ndiswrapper contains essentially two drivers in one - PCI and USB.
>> The PCI driver uses DMA, which should be a strong argument for keeping
>> it in the kernel.
>
> how exactly does it use DMA - how does it allocate the memory it later
> on DMAs into, and how does it typically program that DMA target - is
> there any control over that in the NDIS protocol - or will NDIS drivers
> just write random addresses to the mmio space and then the hardware does
> DMA to/from those addresses? [without the NDIS framework having any
> knowledge about the encoding of those bits?]

Sorry for delay. I'm really not sure. The maintainer of ndiswrapper
is currently offline, and I'm just trying to take care of the basic
stuff.

All I can say is NdisMAllocateSharedMemory maps to
dma_alloc_coherent(), and there are some references to scatter-gather
lists. There is a call to dma_map_single(), which is ultimately
called by the Tx function net_dev->hard_start_xmit.

I understand there is some control from NDIS. At least it can request
memory available for DMA.

> on modern hardware it might even be possible to jail an ndiswrapper
> driver to its own pages via the IOMMU.

It's possible that ndiswrapper would support Vista drivers only on
x86_64, which should always have IOMMU, if I understand correctly.
But it would be nice to have proper support for older XP drivers on x86.

--
Regards,
Pavel Roskin