Re: [PATCH 0/1] uio_pci_generic: extensions to allow access for non-privileged processes

From: Tom Lyon
Date: Thu Apr 01 2010 - 15:27:38 EST

On Thursday 01 April 2010 09:10:57 am Avi Kivity wrote:
> On 04/01/2010 07:06 PM, Tom Lyon wrote:
> > On Thursday 01 April 2010 08:54:14 am Avi Kivity wrote:
> >> On 04/01/2010 06:39 PM, Tom Lyon wrote:
> >>>>> - support for MSI and MSI-X interrupts (the intel 82599 VFs support
> >>>>> only MSI-X)
> >>>>
> >>>> How does a userspace program receive those interrupts?
> >>>
> >>> Same as other UIO drivers - by read()ing an event counter.
> >>
> >> IIRC the usual event counter is /dev/uioX, what's your event counter
> >> now?
> >
> > Exact same mechanism.
> But there are multiple msi-x interrupts, how do you know which one
> triggered?

You don't. This would suck for KVM, I guess, but we'd need major rework of the
generic UIO stuff to have a separate event channel for each MSI-X.

For my purposes, collapsing all the MSI-Xs into one MSI-look-alike is fine,
because I'd be using MSI anyways if I could. The weird Intel 82599 VF only
supports MSI-X.

So one big question is - do we expand the whole UIO framework for KVM
requirements, or do we split off either KVM or non-VM into a separate driver?
Hans or Greg - care to opine?

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