Re: [Xen-devel] [RFC PATCH 09/49] ARM: VGIC: change to level-IRQ compatible IRQ injection interface

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 12/02/18 14:24, Andre Przywara wrote:
> > What would you expect the caller to do on error? Except printing an
> > error message?
> I don't know either. Comparing this to hardware, an IRQ is usually
> fire-and-forget (separating the interrupt line from the interrupt state
> here), so a device doesn't really handle the case when an IRQ does not
> make it through (it can't know easily anyway). However the whole state
> machine might get busted in the process (if no one lowers the line, for
> instance).
> So looking at this printing a message looks like the best choice.
>
> I checked all users of vgic_inject_irq(), at the moment all IRQ numbers
> passed in look safe: they are either hardcoded (timer, evtchn) or
> validated before (hardware IRQs, when they are tied to a virtual IRQ).
> So indeed we *should* never see an invalid IRQ number, at the moment.
> I need to check how this changes with the ITS, though.
>
> So we could change the prototype (back) to void, but print some error
> message if the vgic_get_irq() call fails within vgic_inject_irq().
Sounds good to me. Make sure to have those message using the log level 
guest debug message. I might even be tempt to use dgprintk(...) here so 
they get dropped in non-debug build.
Cheers,

--
Julien Grall

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