Re: [PATCH 1/6] qdev: introduce qapi/hmp command for kick/call event

[Dongli Zhang]

On 4/7/21 6:40 AM, Eduardo Habkost wrote:
> On Thu, Mar 25, 2021 at 10:44:28PM -0700, Dongli Zhang wrote:
>> The virtio device/driver (e.g., vhost-scsi or vhost-net) may hang due to
>> the loss of doorbell kick, e.g.,
>>
>> https://urldefense.com/v3/__https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01711.html__;!!GqivPVa7Brio!NaqdV_o0gMJkUtVWaHyLRwKDa_8MsiuANAqEcM-Ooy4pYE3R1bwPmLdCTkE0gq6gywY$
>>  
>>
>> ... or due to the loss of IRQ, e.g., as fixed by linux kernel commit
>> fe200ae48ef5 ("genirq: Mark polled irqs and defer the real handler").
>>
>> This patch introduces a new debug interface 'DeviceEvent' to DeviceClass
>> to help narrow down if the issue is due to loss of irq/kick. So far the new
>> interface handles only two events: 'call' and 'kick'. Any device (e.g.,
>> virtio/vhost or VFIO) may implement the interface (e.g., via eventfd, MSI-X
>> or legacy IRQ).
>>
>> The 'call' is to inject irq on purpose by admin for a specific device (e.g.,
>> vhost-scsi) from QEMU/host to VM, while the 'kick' is to kick the doorbell
>> on purpose by admin at QEMU/host side for a specific device.
>>
>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> [...]
>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>> index 605d57287a..c7795d4ba5 100644
>> --- a/include/monitor/hmp.h
>> +++ b/include/monitor/hmp.h
>> @@ -129,5 +129,6 @@ void hmp_info_replay(Monitor *mon, const QDict *qdict);
>>  void hmp_replay_break(Monitor *mon, const QDict *qdict);
>>  void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
>>  void hmp_replay_seek(Monitor *mon, const QDict *qdict);
>> +void hmp_x_debug_device_event(Monitor *mon, const QDict *qdict);
>>  
>>  #endif
>> diff --git a/qapi/qdev.json b/qapi/qdev.json
>> index b83178220b..711c4a297a 100644
>> --- a/qapi/qdev.json
>> +++ b/qapi/qdev.json
>> @@ -124,3 +124,33 @@
>>  ##
>>  { 'event': 'DEVICE_DELETED',
>>    'data': { '*device': 'str', 'path': 'str' } }
>> +
>> +##
>> +# @x-debug-device-event:
>> +#
>> +# Generate device event for a specific device queue
>> +#
>> +# @dev: device path
>> +#
>> +# @event: event (e.g., kick or call) to trigger
> 
> Any specific reason to not use an enum here?
> 
> In addition to making the QAPI schema and documentation more
> descriptive, it would save you the work of manually defining the
> DEVICE_EVENT_* constants and implementing get_device_event().

Thank you very much for the suggestion!

I will use enum in json file.

Dongli Zhang

> 
> 
>> +#
>> +# @queue: queue id
>> +#
>> +# Returns: Nothing on success
>> +#
>> +# Since: 6.1
>> +#
>> +# Notes: This is used to debug VM driver hang issue. The 'kick' event is to
>> +#        send notification to QEMU/vhost while the 'call' event is to
>> +#        interrupt VM on purpose.
>> +#
>> +# Example:
>> +#
>> +# -> { "execute": "x-debug-device_event",
>> +#      "arguments": { "dev": "/machine/peripheral/vscsi0", "event": "kick",
>> +#                     "queue": 1 } }
>> +# <- { "return": {} }
>> +#
>> +##
>> +{ 'command': 'x-debug-device-event',
>> +  'data': {'dev': 'str', 'event': 'str', 'queue': 'int'} }
> [...]
>