Re: [PATCH v5 0/8] In-kernel XICS interrupt controller emulation

Alexander Graf
2013-04-28T09:50:49Z

On 27.04.2013, at 10:36, Paul Mackerras wrote:

> On Fri, Apr 26, 2013 at 04:30:37PM +0200, Alexander Graf wrote:
>> Very nice patch set. I've applie 1-7 of it to kvm-ppc-queue. So they will hopefully make it to 3.10.
>>
>> Please check for 8/8 whether
>>
>> a) You want to have a released kernel version without irq routing (irqfd) support. It makes user space's life harder, because you need to maintain backwards compatibility.
>
> If we do a version without irq routing and later add it, old userspace
> should still work, since KVM_IRQ_LINE still works, right? New
> userspace on an old kernel can test the KVM_CAP_IRQ_ROUTING capability
> to see if it can use irqfd. So on the whole, I would like to get it

User space would have to know about 2 different ways of setting interrupts, one through IRQ_LINE and one through whatever XICS device specific ioctl you create :).

This really depends on how quickly you think you could have irqfd support working. If you think it's ready for 3.11, I'd be inclined to say that it's easier for everyone if we don't have to provide any backwards compatibility at all. Then QEMU doesn't need to learn about the irq line setting path that is only ever available on 3.10.

> in, provided of course I can get it tested and sent out before the
> window closes.
>
>> b) Please rebase on top of the current state of things, especially the changed lifecycle assumptions. Devices should now just live until the vm gets destroyed. It gives me way less headaches.
>
> OK, I've done that, but I need to grab David Gibson to get a qemu that
> knows about the new API so I can test it.

Yeah, please sync with him on this whole thing too. Someone will have to write the compat code ;).

Alex