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List:       qemu-block
Subject:    Re: [PATCH v4 3/3] qapi: introduce device-sync-config
From:       Vladimir Sementsov-Ogievskiy <vsementsov () yandex-team ! ru>
Date:       2024-04-30 8:31:19
Message-ID: 2f3f4354-7a98-48e9-84fa-4962f129a26f () yandex-team ! ru
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On 30.04.24 11:19, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
> 
>> Add command to sync config from vhost-user backend to the device. It
>> may be helpful when VHOST_USER_SLAVE_CONFIG_CHANGE_MSG failed or not
>> triggered interrupt to the guest or just not available (not supported
>> by vhost-user server).
>>
>> Command result is racy if allow it during migration. Let's allow the
>> sync only in RUNNING state.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>> ---
>>   hw/block/vhost-user-blk.c |  1 +
>>   hw/virtio/virtio-pci.c    |  9 ++++++++
>>   include/hw/qdev-core.h    |  3 +++
>>   qapi/qdev.json            | 23 +++++++++++++++++++
>>   system/qdev-monitor.c     | 48 +++++++++++++++++++++++++++++++++++++++
>>   5 files changed, 84 insertions(+)
>>
>> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
>> index 091d2c6acf..2f301f380c 100644
>> --- a/hw/block/vhost-user-blk.c
>> +++ b/hw/block/vhost-user-blk.c
>> @@ -588,6 +588,7 @@ static void vhost_user_blk_class_init(ObjectClass *klass, void *data)
>>   
>>       device_class_set_props(dc, vhost_user_blk_properties);
>>       dc->vmsd = &vmstate_vhost_user_blk;
>> +    dc->sync_config = vhost_user_blk_sync_config;
>>       set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
>>       vdc->realize = vhost_user_blk_device_realize;
>>       vdc->unrealize = vhost_user_blk_device_unrealize;
>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> index b1d02f4b3d..0d91e8b5dc 100644
>> --- a/hw/virtio/virtio-pci.c
>> +++ b/hw/virtio/virtio-pci.c
>> @@ -2351,6 +2351,14 @@ static void virtio_pci_dc_realize(DeviceState *qdev, Error **errp)
>>       vpciklass->parent_dc_realize(qdev, errp);
>>   }
>>   
>> +static int virtio_pci_sync_config(DeviceState *dev, Error **errp)
>> +{
>> +    VirtIOPCIProxy *proxy = VIRTIO_PCI(dev);
>> +    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
>> +
>> +    return qdev_sync_config(DEVICE(vdev), errp);
>> +}
>> +
>>   static void virtio_pci_class_init(ObjectClass *klass, void *data)
>>   {
>>       DeviceClass *dc = DEVICE_CLASS(klass);
>> @@ -2367,6 +2375,7 @@ static void virtio_pci_class_init(ObjectClass *klass, void *data)
>>       device_class_set_parent_realize(dc, virtio_pci_dc_realize,
>>                                       &vpciklass->parent_dc_realize);
>>       rc->phases.hold = virtio_pci_bus_reset_hold;
>> +    dc->sync_config = virtio_pci_sync_config;
>>   }
>>   
>>   static const TypeInfo virtio_pci_info = {
>> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
>> index 9228e96c87..87135bdcdf 100644
>> --- a/include/hw/qdev-core.h
>> +++ b/include/hw/qdev-core.h
>> @@ -95,6 +95,7 @@ typedef void (*DeviceUnrealize)(DeviceState *dev);
>>   typedef void (*DeviceReset)(DeviceState *dev);
>>   typedef void (*BusRealize)(BusState *bus, Error **errp);
>>   typedef void (*BusUnrealize)(BusState *bus);
>> +typedef int (*DeviceSyncConfig)(DeviceState *dev, Error **errp);
>>   
>>   /**
>>    * struct DeviceClass - The base class for all devices.
>> @@ -162,6 +163,7 @@ struct DeviceClass {
>>       DeviceReset reset;
>>       DeviceRealize realize;
>>       DeviceUnrealize unrealize;
>> +    DeviceSyncConfig sync_config;
>>   
>>       /**
>>        * @vmsd: device state serialisation description for
>> @@ -546,6 +548,7 @@ bool qdev_hotplug_allowed(DeviceState *dev, Error **errp);
>>    */
>>   HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev);
>>   void qdev_unplug(DeviceState *dev, Error **errp);
>> +int qdev_sync_config(DeviceState *dev, Error **errp);
>>   void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,
>>                                     DeviceState *dev, Error **errp);
>>   void qdev_machine_creation_done(void);
>> diff --git a/qapi/qdev.json b/qapi/qdev.json
>> index facaa0bc6a..fc5e125a45 100644
>> --- a/qapi/qdev.json
>> +++ b/qapi/qdev.json
>> @@ -161,3 +161,26 @@
>>   ##
>>   { 'event': 'DEVICE_UNPLUG_GUEST_ERROR',
>>     'data': { '*device': 'str', 'path': 'str' } }
>> +
>> +##
>> +# @device-sync-config:
>> +#
>> +# Synchronize device configuration from host to guest part.  First,
>> +# copy the configuration from the host part (backend) to the guest
>> +# part (frontend).  Then notify guest software that device
>> +# configuration changed.
> 
> Blank line here, please.
> 
>> +# The command may be used to notify the guest about block device
>> +# capcity change.  Currently only vhost-user-blk device supports
>> +# this.
>> +#
>> +# @id: the device's ID or QOM path
>> +#
>> +# Features:
>> +#
>> +# @unstable: The command is experimental.
>> +#
>> +# Since: 9.1
>> +##
>> +{ 'command': 'device-sync-config',
>> +  'features': [ 'unstable' ],
>> +  'data': {'id': 'str'} }
>> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
>> index 264978aa40..47bfc0506e 100644
>> --- a/system/qdev-monitor.c
>> +++ b/system/qdev-monitor.c
>> @@ -23,6 +23,7 @@
>>   #include "monitor/monitor.h"
>>   #include "monitor/qdev.h"
>>   #include "sysemu/arch_init.h"
>> +#include "sysemu/runstate.h"
>>   #include "qapi/error.h"
>>   #include "qapi/qapi-commands-qdev.h"
>>   #include "qapi/qmp/dispatch.h"
>> @@ -971,6 +972,53 @@ void qmp_device_del(const char *id, Error **errp)
>>       }
>>   }
>>   
>> +int qdev_sync_config(DeviceState *dev, Error **errp)
>> +{
>> +    DeviceClass *dc = DEVICE_GET_CLASS(dev);
>> +
>> +    if (!dc->sync_config) {
>> +        error_setg(errp, "device-sync-config is not supported for '%s'",
>> +                   object_get_typename(OBJECT(dev)));
>> +        return -ENOTSUP;
>> +    }
>> +
>> +    return dc->sync_config(dev, errp);
>> +}
>> +
>> +void qmp_device_sync_config(const char *id, Error **errp)
>> +{
>> +    DeviceState *dev;
>> +
>> +    /*
>> +     * During migration there is a race between syncing`configuration and
>> +     * migrating it (if migrate first, that target would get outdated version),
>> +     * so let's just not allow it.
> 
> Wrap comment lines around column 70 for legibility, please.
> 
>> +     *
>> +     * Moreover, let's not rely on setting up interrupts in paused
>> +     * state, which may be a part of migration process.
> 
> We discussed this in review of v3.  You wanted to check whether the
> problem is real.  Is it?

We discussed it later than I've sent v4 :) No, I didn't check yet.

> 
>> +     */
>> +
>> +    if (migration_is_running()) {
>> +        error_setg(errp, "Config synchronization is not allowed "
>> +                   "during migration");
>> +        return;
>> +    }
>> +
>> +    if (!runstate_is_running()) {
>> +        error_setg(errp, "Config synchronization allowed only in '%s' state, "
> 
> Suggest a line break after errp,
> 
>> +                   "current state is '%s'", RunState_str(RUN_STATE_RUNNING),
>> +                   RunState_str(runstate_get()));
>> +        return;
>> +    }
>> +
>> +    dev = find_device_state(id, true, errp);
>> +    if (!dev) {
>> +        return;
>> +    }
>> +
>> +    qdev_sync_config(dev, errp);
>> +}
>> +
>>   void hmp_device_add(Monitor *mon, const QDict *qdict)
>>   {
>>       Error *err = NULL;
> 

-- 
Best regards,
Vladimir


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