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

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Message-ID: <20080304003723.z79pcavdk4wgoc44@webmail.spamcop.net>
Date:	Tue, 04 Mar 2008 00:37:23 -0500
From:	Pavel Roskin <proski@....org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zan Lynx <zlynx@....org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jon Masters <jcm@...masters.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 2.6.25] module: allow ndiswrapper to use GPL-only
	symbols

Quoting Ingo Molnar <mingo@...e.hu>:

>
> * Pavel Roskin <proski@....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
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