Re: [PATCH v8 0/6] kvm: level irqfd support

Avi Kivity
2012-08-16T18:11:55Z

On 08/11/2012 01:37 AM, Alex Williamson wrote:
> v8:
>
> Trying a new approach. Nobody seems to like the internal IRQ
> source ID object and the interactions it implies between irqfd
> and eoifd, so let's get rid of it. Instead, simply expose
> IRQ source IDs to userspace. This lets the user be in charge
> of freeing them or hanging onto a source ID for later use. They
> can also detach and re-attach components at will. It also opens
> up the possibility that userspace might want to use each IRQ
> source ID for more than one GSI (and avoids the kernel needing
> to manage that). Per suggestions, EOIFD is now IRQ_ACKFD.
>
> I really wanted to add a de-assert-only option to irqfd so the
> irq_ackfd could be fed directly into an irqfd, but I'm dependent
> on the ordering of de-assert _then_ signal an eventfd. Keeping
> that ordering doesn't seem to be possible, especially since irqfd
> uses a workqueue, if I attempt to make that connection. Thanks,

I can't say I'm happy with exposing irq source IDs. It's true that they
correspond to a physical entity so they can't be said to be an
implementation detail, but adding more ABIs has a cost and I can't say
that I see another user for this.

Can you provide a link to the combined irqfd+ackfd implementation? I'm
inclined now to go for the simplest solution possible.

--
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