Re: [Qemu-devel] [RFC][PATCH 23/45] qemu-kvm: Rework MSI-X mask notifier to generic MSI config notifiers

[Jan Kiszka]

On 2011-10-18 15:46, Michael S. Tsirkin wrote:
>>>> To
>>>> have common types, I would prefer to stay with vector config notifiers
>>>> as name then.
>>>>
>>>> Jan
>>>
>>> So we pass in nonsense values and ask all users to know about MSIX rules.
>>> Ugh.
>>>
>>> I do realize msi might change the vector without masking.
>>> We can either artificially call mask before value change
>>> and unmask after, or use 3 notifiers: mask,unmask,config.
>>> Add a comment that config is invoked when configuration
>>> for an unmasked vector is changed, and that
>>> it can only happen for msi, not msix.
>>
>> I see no need in complicating the API like this. MSI-X still needs the
>> config information on unmask, so let's just consistently pass it via the
>> unified config notifier instead of forcing the consumers to create yet
>> two more handlers. I really do not see the benefit for the consumer.
>>
>> Jan
>>
> 
> The benefit is a clearer API, where all parameters you get are valid,
> so you do not need to go read the spec to see what is OK to use.
> Generally, encoding events in flags is more error
> prone than using different notifiers for different events.
> 
> E.g. _unmask and _mask make
> it obvious that they are called on mask and on unmask
> respectively.
> OTOH _config_change(bool mask) is unclear: is 'mask' the new
> state or the old state?
> 
> It might be just my taste, but I usually prefer multiple
> functions doing one thing each rather than a single
> function doing multiple things. It shouldn't be too hard ...

The impact on the user side (device models) will be larger while the
work in those different handlers will be widely the same (check my
series, e.g. the virtio handler). But it's still just a guess of mine as
well.

Jan

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