Re: [PATCH 4/4] qapi: introduce CONFIG_READ event

[Markus Armbruster <armbru@redhat.com>]

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 |  1 +
>  monitor/monitor.c      |  1 +
>  qapi/qdev.json         | 22 ++++++++++++++++++++++
>  softmmu/qdev-monitor.c |  5 +++++
>  5 files changed, 38 insertions(+)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index dd4620462b..f24f8ff03d 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"
> @@ -541,6 +542,10 @@ static uint64_t virtio_pci_config_read(void *opaque, hwaddr addr,
>      }
>      addr -= config;
>  
> +    if (vdev->generation > 0) {
> +        qdev_config_read_event(DEVICE(proxy));
> +    }
> +
>      switch (size) {
>      case 1:
>          val = virtio_config_readb(vdev, addr);
> @@ -1728,6 +1733,10 @@ static uint64_t virtio_pci_device_read(void *opaque, hwaddr addr,
>          return UINT64_MAX;
>      }
>  
> +    if (vdev->generation > 0) {
> +        qdev_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 949a3672cb..f0b0eab07e 100644
> --- a/include/monitor/qdev.h
> +++ b/include/monitor/qdev.h
> @@ -39,6 +39,7 @@ DeviceState *qdev_device_add_from_qdict(const QDict *opts,
>  const char *qdev_set_id(DeviceState *dev, char *id, Error **errp);
>  
>  void qdev_hotplug_device_on_event(DeviceState *dev);
> +void qdev_config_read_event(DeviceState *dev);
>  
>  DeviceAndPath *qdev_new_device_and_path(DeviceState *dev);
>  
> diff --git a/monitor/monitor.c b/monitor/monitor.c
> index 941f87815a..f8aa91b190 100644
> --- a/monitor/monitor.c
> +++ b/monitor/monitor.c
> @@ -315,6 +315,7 @@ static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
>      [QAPI_EVENT_QUORUM_FAILURE]    = { 1000 * SCALE_MS },
>      [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
>      [QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE] = { 1000 * SCALE_MS },
> +    [QAPI_EVENT_X_CONFIG_READ]   = { 300 * SCALE_MS },
>  };
>  
>  /*
> diff --git a/qapi/qdev.json b/qapi/qdev.json
> index 2468f8bddf..37a8785b81 100644
> --- a/qapi/qdev.json
> +++ b/qapi/qdev.json
> @@ -329,3 +329,25 @@
>  # Since: 8.2
>  ##
>  { 'command': 'x-device-sync-config', 'data': {'id': 'str'} }
> +
> +##
> +# @X_CONFIG_READ:
> +#
> +# Emitted whenever guest reads virtio device config after config change.
> +#
> +# @device: device name
> +#
> +# @path: device path
> +#
> +# Since: 5.0.1-24
> +#
> +# Example:
> +#
> +# <- { "event": "X_CONFIG_READ",
> +#      "data": { "device": "virtio-net-pci-0",
> +#                "path": "/machine/peripheral/virtio-net-pci-0" },
> +#      "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
> +#
> +##
> +{ 'event': 'X_CONFIG_READ',
> +  'data': { '*device': 'str', 'path': 'str' } }

The commit message talks about event CONFIG_READ, but you actually name
it x-device-sync-config.

I figure you use x- to signify "unstable".  Please use feature flag
'unstable' for that.  See docs/devel/qapi-code-gen.rst section
"Features", in particular "Special features", and also the note on x- in
section "Naming rules and reserved names".

The name CONFIG_READ feels overly generic for something that makes sense
only with virtio devices.

> diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> index b485375049..d0f022e925 100644
> --- a/softmmu/qdev-monitor.c
> +++ b/softmmu/qdev-monitor.c
> @@ -1252,3 +1252,8 @@ void qdev_hotplug_device_on_event(DeviceState *dev)
>      dev->device_on_event_sent = true;
>      qapi_event_send_x_device_on(dev->id, dev->canonical_path);
>  }
> +
> +void qdev_config_read_event(DeviceState *dev)
> +{
> +    qapi_event_send_x_config_read(dev->id, dev->canonical_path);
> +}