Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd

[Avi Kivity <avi@redhat.com>]

On 08/22/2012 03:41 AM, Michael S. Tsirkin wrote:
>> 
>> I assumed you were pointing out the level vs edge interaction.  If we
>> call that a userspace bug, I can just drop this.  Thanks,
>> 
>> Alex
> 
> level is userspace bug I think :)

I don't see how it's a bug.  Suppose we have a vfio device that shares a
gsi with an emulated device.  The emulated device naturally uses
KVM_IRQ_LINE (it has no need to re-sample on ADN), while vfio naturally
has to use irqfd.

Note one would expect that each irqfd gets its own irq source id, since
they are all independent level sources.  The reason they don't is that
we shut them down anyway and let the sources re-trigger (it is more
accurate to say that they have no irq source id, but that would just
muddle the implementation).

Alex, if the conclusion is that we do need this patch, then please add a
comment explaining why we can share the source id among all irqfd users.

-- 
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