[Xen-devel] Re: Reversing the DMA handle

[Pete Zaitcev <zaitcev@xxxxxxxxxx>]

On Wed, 10 Jan 2007 05:25:08 +0200, Muli Ben-Yehuda <muli@xxxxxxxxxx> wrote:
> On Tue, Jan 09, 2007 at 05:17:10PM -0800, Pete Zaitcev wrote:

> > I maintain a component in Linux kernel, called usbmon. It provides for
> > snooping of USB traffic, analoguously to tcpdump. Due to pequliarities
> > of USB API in Linux, usbmon has to take a DMA address (coming from
> > dma_alloc_coherent() typically), find the corresponding PFN and call
> > pkmap()/memcpy()/pkunmap().

> Regardless of Xen, how is this supposed to work in the presence of
> IOMMUs?

It cannot, generically speaking. So, no usbmon on Calgari. But for
a specific IOMMU I can place necessary hooks. I am looking at SWIOTLB
currently. And don't forget that it only works on cache-coherent
architectures, so no SPARC support ever.

-- Pete

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