Re: [PATCH] vfio/migration: Send migration event before device state transition

[Markus Armbruster <armbru@redhat.com>]

Avihai Horon <avihaih@nvidia.com> writes:

> Currently, VFIO device migration event is sent after the device state
> transition has been completed. However, it may be useful to additionally
> send a "prepare" event before the state transition, to notify users that
> it's about to happen.
>
> For example, in some cases with heavy resource utilization, stopping the
> VFIO device may take a long time. In time-sensitive scenarios, the
> management application that consumes the event may be notified about the
> state transition too late.
>
> To overcome this issue, send an additional "prepare" migration event
> before the device state transition.
>
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
>  qapi/vfio.json      | 33 +++++++++++++++++++++++++++++++++
>  hw/vfio/migration.c | 18 +++++++++++++-----
>  2 files changed, 46 insertions(+), 5 deletions(-)
>
> diff --git a/qapi/vfio.json b/qapi/vfio.json
> index a1a9c5b673..de41211f1d 100644
> --- a/qapi/vfio.json
> +++ b/qapi/vfio.json
> @@ -66,3 +66,36 @@
>        'qom-path': 'str',
>        'device-state': 'QapiVfioMigrationState'
>    } }
> +
> +##
> +# @VFIO_MIGRATION_PREPARE:
> +#
> +# This event is emitted when a VFIO device migration state is about to
> +# be changed.  Note that even if this event is received for state X,
> +# the VFIO device may transition to a different state if the original
> +# state transition to X failed.
> +#
> +# @device-id: The device's id, if it has one.
> +#
> +# @qom-path: The device's QOM path.
> +#
> +# @device-state: The new device migration state that is about to be
> +#     changed.
> +#
> +# Since: 11.0
> +#
> +# .. qmp-example::
> +#
> +#     <- { "timestamp": { "seconds": 1713771323, "microseconds": 212268 },
> +#          "event": "VFIO_MIGRATION_PREPARE",
> +#          "data": {
> +#              "device-id": "vfio_dev1",
> +#              "qom-path": "/machine/peripheral/vfio_dev1",
> +#              "device-state": "stop" } }
> +##
> +{ 'event': 'VFIO_MIGRATION_PREPARE',
> +  'data': {
> +      'device-id': 'str',
> +      'qom-path': 'str',
> +      'device-state': 'QapiVfioMigrationState'
> +  } }

The QAPI schema is fine, so

Acked-by: Markus Armbruster <armbru@redhat.com>

Whether the event makes sense I have no idea.  I'm leaving that
judgement to the migration and VFIO maintainers.