Re: [Xen-devel] [PATCH v2] x86/vpt: guarantee the return value of pt_update_irq() set in vIRR or PIR

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.10.17 at 15:46, <chao.gao@xxxxxxxxx> wrote:
> On Mon, Oct 16, 2017 at 08:26:09AM -0600, Jan Beulich wrote:
>>>>> On 16.10.17 at 15:13, <chao.gao@xxxxxxxxx> wrote:
>>> On Mon, Oct 16, 2017 at 07:15:16AM -0600, Jan Beulich wrote:
>>>>>>> On 13.10.17 at 07:10, <chao.gao@xxxxxxxxx> wrote:
>>>>> --- a/xen/arch/x86/hvm/irq.c
>>>>> +++ b/xen/arch/x86/hvm/irq.c
>>>>> @@ -168,11 +168,13 @@ void hvm_gsi_deassert(struct domain *d, unsigned 
>>>>> int 
> gsi)
>>>>>      spin_unlock(&d->arch.hvm_domain.irq_lock);
>>>>>  }
>>>>>  
>>>>> -void hvm_isa_irq_assert(
>>>>> -    struct domain *d, unsigned int isa_irq)
>>>>> +int hvm_isa_irq_assert(struct domain *d, unsigned int isa_irq,
>>>>> +                       int (*get_vector)(const struct domain *d,
>>>>> +                                         unsigned int gsi))
>>>>>  {
>>>>>      struct hvm_irq *hvm_irq = hvm_domain_irq(d);
>>>>>      unsigned int gsi = hvm_isa_irq_to_gsi(isa_irq);
>>>>> +    int vector = 0;
>>>>
>>>>Why zero (which is valid aiui) instead of e.g. -1?
>>> 
>>> vector also serves as the return value. I want to return 0 if no
>>> callback is set.  And the callback, get_vector, can override the return
>>> value. Do you think it is reasonable?
>>
>>Why "also" - being the return value is the only purpose of "vector".
>>And as said - zero is a valid vector, and I wouldn't like to see the
>>function return a valid but meaningless vector number.
> 
> But if no callback is set, would it be a little weird to return -1 which
> always means failure?

To me, -1 doesn't mean "failure" here, but "no valid vector".

Jan


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