Re: [PATCH v3 5/5] qapi: introduce CONFIG_READ event

[Markus Armbruster]

Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:

> Send a new event when guest reads virtio-pci config after
> virtio_notify_config() call.
>
> That's useful to check that guest fetched modified config, for example
> after resizing disk backend.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  hw/virtio/virtio-pci.c |  9 +++++++++
>  include/monitor/qdev.h |  2 ++
>  monitor/monitor.c      |  1 +
>  qapi/qdev.json         | 33 +++++++++++++++++++++++++++++++++
>  stubs/qdev.c           |  6 ++++++
>  system/qdev-monitor.c  |  6 ++++++
>  6 files changed, 57 insertions(+)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 92afbae71c..c0c158dae2 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -23,6 +23,7 @@
>  #include "hw/boards.h"
>  #include "hw/virtio/virtio.h"
>  #include "migration/qemu-file-types.h"
> +#include "monitor/qdev.h"
>  #include "hw/pci/pci.h"
>  #include "hw/pci/pci_bus.h"
>  #include "hw/qdev-properties.h"
> @@ -530,6 +531,10 @@ static uint64_t virtio_pci_config_read(void *opaque, 
> hwaddr addr,
>      }
>      addr -= config;
>  
> +    if (vdev->generation > 0) {
> +        qdev_virtio_config_read_event(DEVICE(proxy));
> +    }
> +
>      switch (size) {
>      case 1:
>          val = virtio_config_readb(vdev, addr);
> @@ -1884,6 +1889,10 @@ static uint64_t virtio_pci_device_read(void *opaque, 
> hwaddr addr,
>          return UINT64_MAX;
>      }
>  
> +    if (vdev->generation > 0) {
> +        qdev_virtio_config_read_event(DEVICE(proxy));
> +    }
> +
>      switch (size) {
>      case 1:
>          val = virtio_config_modern_readb(vdev, addr);
> diff --git a/include/monitor/qdev.h b/include/monitor/qdev.h
> index 1d57bf6577..fc9a834dca 100644
> --- a/include/monitor/qdev.h
> +++ b/include/monitor/qdev.h
> @@ -36,4 +36,6 @@ DeviceState *qdev_device_add_from_qdict(const QDict *opts,
>   */
>  const char *qdev_set_id(DeviceState *dev, char *id, Error **errp);
>  
> +void qdev_virtio_config_read_event(DeviceState *dev);
> +
>  #endif
> diff --git a/monitor/monitor.c b/monitor/monitor.c
> index 01ede1babd..5b06146503 100644
> --- a/monitor/monitor.c
> +++ b/monitor/monitor.c
> @@ -316,6 +316,7 @@ static MonitorQAPIEventConf 
> monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
>      [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
>      [QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE] = { 1000 * SCALE_MS },
>      [QAPI_EVENT_HV_BALLOON_STATUS_REPORT] = { 1000 * SCALE_MS },
> +    [QAPI_EVENT_VIRTIO_CONFIG_READ] = { 300 * SCALE_MS },

All the other rate-limited events use 1s.  Why 0.3s for this one?

>  };
>  
>  /*
> diff --git a/qapi/qdev.json b/qapi/qdev.json
> index e8be79c3d5..29a4f47360 100644
> --- a/qapi/qdev.json
> +++ b/qapi/qdev.json
> @@ -182,3 +182,36 @@
>  { 'command': 'device-sync-config',
>    'features': [ 'unstable' ],
>    'data': {'id': 'str'} }
> +
> +##
> +# @VIRTIO_CONFIG_READ:
> +#
> +# Emitted whenever guest reads virtio device configuration after
> +# configuration change.

Is it emitted whenever the guest reads, or only when it reads after a
configuration change?

> +#
> +# The event may be used in pair with device-sync-config. It shows
> +# that guest has re-read updated configuration. It doesn't
> +# guarantee that guest successfully handled it and updated the
> +# view of the device for the user, but still it's a kind of
> +# success indicator.

The event is virtio-only.  device-sync-config isn't.  Why?

> +#
> +# @device: device name
> +#
> +# @path: device path
> +#
> +# Features:
> +#
> +# @unstable: The event is experimental.
> +#

Missing:

   # Note: This event is rate-limited.
   #

> +# Since: 9.1
> +#
> +# Example:
> +#
> +#     <- { "event": "VIRTIO_CONFIG_READ",
> +#          "data": { "device": "virtio-net-pci-0",
> +#                    "path": "/machine/peripheral/virtio-net-pci-0" },
> +#          "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
> +##
> +{ 'event': 'VIRTIO_CONFIG_READ',
> +  'features': [ 'unstable' ],
> +  'data': { '*device': 'str', 'path': 'str' } }
> diff --git a/stubs/qdev.c b/stubs/qdev.c
> index 6869f6f90a..ab6c4afe0b 100644
> --- a/stubs/qdev.c
> +++ b/stubs/qdev.c
> @@ -26,3 +26,9 @@ void qapi_event_send_device_unplug_guest_error(const char 
> *device,
>  {
>      /* Nothing to do. */
>  }
> +
> +void qapi_event_send_virtio_config_read(const char *device,
> +                                        const char *path)
> +{
> +    /* Nothing to do. */
> +}
> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> index cb35ea0b86..8a2ca77fde 100644
> --- a/system/qdev-monitor.c
> +++ b/system/qdev-monitor.c
> @@ -26,6 +26,7 @@
>  #include "sysemu/runstate.h"
>  #include "qapi/error.h"
>  #include "qapi/qapi-commands-qdev.h"
> +#include "qapi/qapi-events-qdev.h"
>  #include "qapi/qmp/dispatch.h"
>  #include "qapi/qmp/qdict.h"
>  #include "qapi/qmp/qerror.h"
> @@ -1206,3 +1207,8 @@ bool qmp_command_available(const QmpCommand *cmd, Error 
> **errp)
>      }
>      return true;
>  }
> +
> +void qdev_virtio_config_read_event(DeviceState *dev)
> +{
> +    qapi_event_send_virtio_config_read(dev->id, dev->canonical_path);
> +}

Which configuration needs the stub?