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SubjectRe: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity
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On 9/28/2021 2:12 AM, Jason Gunthorpe wrote:
> On Mon, Sep 27, 2021 at 04:46:48PM -0600, Alex Williamson wrote:
>>> + enum { MAX_STATE = VFIO_DEVICE_STATE_RESUMING };
>>> + static const u8 vfio_from_state_table[MAX_STATE + 1][MAX_STATE + 1] = {
>>> + [VFIO_DEVICE_STATE_STOP] = {
>>> + [VFIO_DEVICE_STATE_RUNNING] = 1,
>>> + [VFIO_DEVICE_STATE_RESUMING] = 1,
>>> + },
>> Our state transition diagram is pretty weak on reachable transitions
>> out of the _STOP state, why do we select only these two as valid?
> I have no particular opinion on specific states here, however adding
> more states means more stuff for drivers to implement and more risk
> driver writers will mess up this uAPI.

_STOP == 000b => Device Stopped, not saving or resuming (from UAPI).

This is the default initial state and not RUNNING.

The user application should move device from STOP => RUNNING or STOP =>
RESUMING.

Maybe we need to extend the comment in the UAPI file.

>
> So only on those grounds I'd suggest to keep this to the minimum
> needed instead of the maximum logically possible..
>
> Also, probably the FSM comment from the uapi header file should be
> moved into a function comment above this function?
>
> Jason

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