[prev in list] [next in list] [prev in thread] [next in thread] 

List:       qemu-block
Subject:    Re: [PATCH v3 5/5] qapi: introduce CONFIG_READ event
From:       Vladimir Sementsov-Ogievskiy <vsementsov () yandex-team ! ru>
Date:       2024-04-29 9:02:51
Message-ID: 539ee069-39ab-432e-b6ee-29221d372c0f () yandex-team ! ru
[Download RAW message or body]

On 24.04.24 15:11, Markus Armbruster wrote:
> 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?

No actual reason, just seemed to me that 1s is too much. Should be better to keep all \
limits to be the same, until no concrete reason to break it.

> 
> > };
> > 
> > /*
> > 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?

Hmm, it's emitted only when vdev->generation > 0, which generally mean that there was \
at least one call to virtio_notify_config()... That's not the logic, which could be \
simply described here.


Actually, now I think that event was a premature improvement. In our final downstream \
solution only the command device-sync-config is used, not the event. I see that the \
concept of the event is objectionable, I think, I'll better just drop it in v4.

> 
> > +#
> > +# 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?
> 

-- 
Best regards,
Vladimir


[prev in list] [next in list] [prev in thread] [next in thread]