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

[Pavel Roskin]

Quoting Ingo Molnar <mingo@xxxxxxx>:

> * Pavel Roskin <proski@xxxxxxx> 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
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