On Wed, 29 Sep 2021 13:44:10 +0300
Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote:
> 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.
include/uapi/linux/vfio.h:
...
* +------- _RESUMING
* |+------ _SAVING
* ||+----- _RUNNING
* |||
* 000b => Device Stopped, not saving or resuming
* 001b => Device running, which is the default state
^^^^^^^^^^^^^^^^^^^^^^^^^^
...
* State transitions:
*
* _RESUMING _RUNNING Pre-copy Stop-and-copy _STOP
* (100b) (001b) (011b) (010b) (000b)
* 0. Running or default state
* |
^^^^^^^^^^^^^
...
* 0. Default state of VFIO device is _RUNNING when the user application starts.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The uAPI is pretty clear here. A default state of _STOP is not
compatible with existing devices and userspace that does not support
migration. Thanks,
Alex
