Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

[Avi Kivity <avi@redhat.com>]

On 08/31/2011 07:59 PM, Blue Swirl wrote:
> >
> >  That makes it impossible to migrate level-triggered irq lines.  Or at least,
> >  the receiver has to remember the state, instead of (or in addition to) the
> >  sender.
>
> Both ends probably need to remember the state. That should work
> without any multiphase restores and transient suppressors.

State should always correspond to real hardware state - a flip flop or 
capacitor.  Input is not state, it is input.

> It might be also possible to introduce stateful signal lines which
> save and restore their state, then the receiving end could check what
> is the current level. However, if you consider that the devices may be
> restored in random order, if the IRQ line device happens to be
> restored later, the receiver would still get wrong information. Adding
> priorities could solve this, but I think stateless IRQs are the only
> sane way.

I agree that irqs should be stateless, since they don't have any memory 
associated.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.