Re: [PATCH v2 1/2] qapi/machine.json: add DEVICE_UNPLUG_ERROR QAPI event

[Markus Armbruster]

Daniel Henrique Barboza <danielhb413@gmail.com> writes:

> At this moment we only provide one event to report a hotunplug error,
> MEM_UNPLUG_ERROR. As of Linux kernel 5.12 and QEMU 6.0.0, the pseries
> machine is now able to report unplug errors for other device types, such
> as CPUs.
>
> Instead of creating a (device_type)_UNPLUG_ERROR for each new device,
> create a generic DEVICE_UNPLUG_ERROR event that can be used by all
> unplug errors in the future.
>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>  qapi/machine.json | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 58a9c86b36..f0c7e56be0 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1274,3 +1274,26 @@
>  ##
>  { 'event': 'MEM_UNPLUG_ERROR',
>    'data': { 'device': 'str', 'msg': 'str' } }
> +
> +##
> +# @DEVICE_UNPLUG_ERROR:
> +#
> +# Emitted when a device hot unplug error occurs.
> +#
> +# @device: device name
> +#
> +# @msg: Informative message
> +#
> +# Since: 6.1
> +#
> +# Example:
> +#
> +# <- { "event": "DEVICE_UNPLUG_ERROR"
> +#      "data": { "device": "dimm1",
> +#                "msg": "Memory hotunplug rejected by the guest for device 
> dimm1"
> +#      },
> +#      "timestamp": { "seconds": 1615570772, "microseconds": 202844 } }
> +#
> +##
> +{ 'event': 'DEVICE_UNPLUG_ERROR',
> +  'data': { 'device': 'str', 'msg': 'str' } }

Missing: update of device_add's doc comment in qdev.json:

    # Notes: When this command completes, the device may not be removed from the
    #        guest.  Hot removal is an operation that requires guest 
cooperation.
    #        This command merely requests that the guest begin the hot removal
    #        process.  Completion of the device removal process is signaled 
with a
    #        DEVICE_DELETED event. Guest reset will automatically complete 
removal
    #        for all devices.

This sure could use some polish.

If I understand things correctly, we're aiming for the following device
unplug protocol:

   Unplug the device with device_del (or possibly equivalent)

   If we know we can't unplug the device, fail immediately.  Also emit
   DEVICE_UNPLUG_ERROR.

   If possible, unplug the device synchronously and succeed.  Also emit
   DEVICE_DELETED.

   Else, initiate unplug and succeed.

   When unplug finishes, emit either DEVICE_DELETED or
   DEVICE_UNPLUG_ERROR.

   For some machines and devices, unplug may never finish.

Correct?

Any particular reason for not putting event DEVICE_UNPLUG_ERROR next to
DEVICE_DELETED in qdev.json?