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

[Vladimir Sementsov-Ogievskiy]

On 17.10.23 18:00, 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 |  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.

will fix

> 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".

OK, will do.

Hmm, it say

   Names beginning with ``x-`` used to signify "experimental".  This
   convention has been replaced by special feature "unstable".

"replaced".. So, I should use "unstable" flag without "x-" prefix? Can't find an example. Seems 
"unstable" always used together with "x-".

Also, nothing said about events. Is using "X_" wrong idea? Should it be 
x-SOME_EVENT instead?

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

Hmm, right.. I think, we can say same thing about DEVICE_UNPLUG_GUEST_ERROR.

So, what about DEVICE_GUEST_READ_CONFIG ?

> > 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);
> > +}

--
Best regards,
Vladimir