linux-kernel - Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity

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Date:   Tue, 28 Sep 2021 14:18:44 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Kirti Wankhede <kwankhede@...dia.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
 transition validity

On Tue, 28 Sep 2021 16:35:50 -0300
Jason Gunthorpe <jgg@...pe.ca> wrote:

> On Tue, Sep 28, 2021 at 01:19:58PM -0600, Alex Williamson wrote:
> 
> > In defining the device state, we tried to steer away from defining it
> > in terms of the QEMU migration API, but rather as a set of controls
> > that could be used to support that API to leave us some degree of
> > independence that QEMU implementation might evolve.  
> 
> That is certainly a different perspective, it would have been
> better to not express this idea as a FSM in that case...
> 
> So each state in mlx5vf_pci_set_device_state() should call the correct
> combination of (un)freeze, (un)quiesce and so on so each state
> reflects a defined operation of the device?

I'd expect so, for instance the implementation of entering the _STOP
state presumes a previous state that where the device is apparently
already quiesced.  That doesn't support a direct _RUNNING -> _STOP
transition where I argued in the linked threads that those states
should be reachable from any other state.  Thanks,

Alex