Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag

[Paolo Bonzini]

On 06/09/2016 07:27, Peter Xu wrote:
> Maybe I haven't explained the idea very clearly, but device-IOTLB is
> not a "flush" of whole device cache. It still needs a IOMMUTLBEntry,
> and works just like how general IOMMU invalidations. E.g., we can do
> device-IOTLB invalidation for a single 4K page.

Yes, it can be FLUSHED_ENTRY and CHANGED_ENTRY or
INVALIDATE_ENTRY/CHANGE_ENTRY.

> However, I agree with you that the namings are confusing, maybe at
> least we should introduce IOMMU_NOTIFIER_* macros, though instead of a
> _FLUSH one, we can have:
> 
>     IOMMU_NOTIFIER_NONE = -1,
>     IOMMU_NOTIFIER_DEVICE_INVALIDATE = 0,
>     IOMMU_NOTIFIER_IOTLB_CHANGED = 1,

I suggest making the names more similar:

- two participles (invalidated/changed) or two imperatives
(invalidate!/change!);

- choose whether to keep the verb first ("invalidate device") or keep
the noun first ("IOTLB changed"), and stick with one convention.

> To clarify that these are two non-overlapped cases.

If they are not overlapping, they really should be using a bitmask or
multiple callbacks in a struct...

Paolo