[PATCH v4 0/3] vhost-user-blk: live resize additional APIs

[PATCH v4 0/3] vhost-user-blk: live resize additional APIs

[Vladimir Sementsov-Ogievskiy]

v4:
Fixes 01-02 from v3 are already merged.
02: new, split out from 03
03: refacting vhost_user_blk_handle_config_change() split out to 02
    drop current_run_state_str() helper
    some rewordings (Markus)

Vladimir Sementsov-Ogievskiy (3):
  qdev-monitor: add option to report GenericError from find_device_state
  vhost-user-blk: split vhost_user_blk_sync_config()
  qapi: introduce device-sync-config

 hw/block/vhost-user-blk.c | 27 ++++++++++++-----
 hw/virtio/virtio-pci.c    |  9 ++++++
 include/hw/qdev-core.h    |  3 ++
 qapi/qdev.json            | 23 ++++++++++++++
 system/qdev-monitor.c     | 63 ++++++++++++++++++++++++++++++++++++---
 5 files changed, 114 insertions(+), 11 deletions(-)

-- 
2.34.1

[PATCH v4 1/3] qdev-monitor: add option to report GenericError from find_device_state

[Vladimir Sementsov-Ogievskiy]

Here we just prepare for the following patch, making possible to report
GenericError as recommended.

This patch doesn't aim to prevent further use of DeviceNotFound by
future interfaces:

 - find_device_state() is used in blk_by_qdev_id() and qmp_get_blk()
   functions, which may lead to spread of DeviceNotFound anyway
 - also, nothing prevent simply copy-pasting find_device_state() calls
   with false argument

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 system/qdev-monitor.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
index 6af6ef7d66..264978aa40 100644
--- a/system/qdev-monitor.c
+++ b/system/qdev-monitor.c
@@ -879,13 +879,20 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
     object_unref(OBJECT(dev));
 }
 
-static DeviceState *find_device_state(const char *id, Error **errp)
+/*
+ * Note that creating new APIs using error classes other than GenericError is
+ * not recommended. Set use_generic_error=true for new interfaces.
+ */
+static DeviceState *find_device_state(const char *id, bool use_generic_error,
+                                      Error **errp)
 {
     Object *obj = object_resolve_path_at(qdev_get_peripheral(), id);
     DeviceState *dev;
 
     if (!obj) {
-        error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
+        error_set(errp,
+                  (use_generic_error ?
+                   ERROR_CLASS_GENERIC_ERROR : ERROR_CLASS_DEVICE_NOT_FOUND),
                   "Device '%s' not found", id);
         return NULL;
     }
@@ -950,7 +957,7 @@ void qdev_unplug(DeviceState *dev, Error **errp)
 
 void qmp_device_del(const char *id, Error **errp)
 {
-    DeviceState *dev = find_device_state(id, errp);
+    DeviceState *dev = find_device_state(id, false, errp);
     if (dev != NULL) {
         if (dev->pending_deleted_event &&
             (dev->pending_deleted_expires_ms == 0 ||
@@ -1070,7 +1077,7 @@ BlockBackend *blk_by_qdev_id(const char *id, Error **errp)
 
     GLOBAL_STATE_CODE();
 
-    dev = find_device_state(id, errp);
+    dev = find_device_state(id, false, errp);
     if (dev == NULL) {
         return NULL;
     }
-- 
2.34.1

[PATCH v4 2/3] vhost-user-blk: split vhost_user_blk_sync_config()

[Vladimir Sementsov-Ogievskiy]

Split vhost_user_blk_sync_config() out from
vhost_user_blk_handle_config_change(), to be reused in the following
commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 hw/block/vhost-user-blk.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 9e6bbc6950..091d2c6acf 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -88,27 +88,39 @@ static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
     s->blkcfg.wce = blkcfg->wce;
 }
 
+static int vhost_user_blk_sync_config(DeviceState *dev, Error **errp)
+{
+    int ret;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
+                               vdev->config_len, errp);
+    if (ret < 0) {
+        return ret;
+    }
+
+    memcpy(vdev->config, &s->blkcfg, vdev->config_len);
+    virtio_notify_config(vdev);
+
+    return 0;
+}
+
 static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
 {
     int ret;
-    VirtIODevice *vdev = dev->vdev;
-    VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
     Error *local_err = NULL;
 
     if (!dev->started) {
         return 0;
     }
 
-    ret = vhost_dev_get_config(dev, (uint8_t *)&s->blkcfg,
-                               vdev->config_len, &local_err);
+    ret = vhost_user_blk_sync_config(DEVICE(dev->vdev), &local_err);
     if (ret < 0) {
         error_report_err(local_err);
         return ret;
     }
 
-    memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
-    virtio_notify_config(dev->vdev);
-
     return 0;
 }
 
-- 
2.34.1

Re: [PATCH v4 2/3] vhost-user-blk: split vhost_user_blk_sync_config()

[Markus Armbruster]

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

> Split vhost_user_blk_sync_config() out from
> vhost_user_blk_handle_config_change(), to be reused in the following
> commit.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  hw/block/vhost-user-blk.c | 26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 9e6bbc6950..091d2c6acf 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -88,27 +88,39 @@ static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
>      s->blkcfg.wce = blkcfg->wce;
>  }
>  
> +static int vhost_user_blk_sync_config(DeviceState *dev, Error **errp)
> +{
> +    int ret;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);

Note for later: all this function does with paramter @dev is cast it to
VirtIODevice *.

> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
> +
> +    ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> +                               vdev->config_len, errp);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    memcpy(vdev->config, &s->blkcfg, vdev->config_len);
> +    virtio_notify_config(vdev);
> +
> +    return 0;
> +}
> +
>  static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
>  {
>      int ret;
> -    VirtIODevice *vdev = dev->vdev;
> -    VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
>      Error *local_err = NULL;
>  
>      if (!dev->started) {
>          return 0;
>      }
>  
> -    ret = vhost_dev_get_config(dev, (uint8_t *)&s->blkcfg,
> -                               vdev->config_len, &local_err);
> +    ret = vhost_user_blk_sync_config(DEVICE(dev->vdev), &local_err);

dev->vdev is a VirtIODevice *.  You cast it to DeviceState * for
vhost_user_blk_sync_config(), which casts it right back.

Could you simply pass it as is instead?

>      if (ret < 0) {
>          error_report_err(local_err);
>          return ret;
>      }
>  
> -    memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
> -    virtio_notify_config(dev->vdev);
> -
>      return 0;
>  }

Re: [PATCH v4 2/3] vhost-user-blk: split vhost_user_blk_sync_config()

[Vladimir Sementsov-Ogievskiy]

On 30.04.24 11:15, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
> 
>> Split vhost_user_blk_sync_config() out from
>> vhost_user_blk_handle_config_change(), to be reused in the following
>> commit.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>> ---
>>   hw/block/vhost-user-blk.c | 26 +++++++++++++++++++-------
>>   1 file changed, 19 insertions(+), 7 deletions(-)
>>
>> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
>> index 9e6bbc6950..091d2c6acf 100644
>> --- a/hw/block/vhost-user-blk.c
>> +++ b/hw/block/vhost-user-blk.c
>> @@ -88,27 +88,39 @@ static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
>>       s->blkcfg.wce = blkcfg->wce;
>>   }
>>   
>> +static int vhost_user_blk_sync_config(DeviceState *dev, Error **errp)
>> +{
>> +    int ret;
>> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> 
> Note for later: all this function does with paramter @dev is cast it to
> VirtIODevice *.
> 
>> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
>> +
>> +    ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
>> +                               vdev->config_len, errp);
>> +    if (ret < 0) {
>> +        return ret;
>> +    }
>> +
>> +    memcpy(vdev->config, &s->blkcfg, vdev->config_len);
>> +    virtio_notify_config(vdev);
>> +
>> +    return 0;
>> +}
>> +
>>   static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
>>   {
>>       int ret;
>> -    VirtIODevice *vdev = dev->vdev;
>> -    VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
>>       Error *local_err = NULL;
>>   
>>       if (!dev->started) {
>>           return 0;
>>       }
>>   
>> -    ret = vhost_dev_get_config(dev, (uint8_t *)&s->blkcfg,
>> -                               vdev->config_len, &local_err);
>> +    ret = vhost_user_blk_sync_config(DEVICE(dev->vdev), &local_err);
> 
> dev->vdev is a VirtIODevice *.  You cast it to DeviceState * for
> vhost_user_blk_sync_config(), which casts it right back.
> 
> Could you simply pass it as is instead?

vhost_user_blk_sync_config() is generic handler, which will be used as ->sync_config() in the following commit, so it's good and convenient for it to have DeviceState* argument.

> 
>>       if (ret < 0) {
>>           error_report_err(local_err);
>>           return ret;
>>       }
>>   
>> -    memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
>> -    virtio_notify_config(dev->vdev);
>> -
>>       return 0;
>>   }
> 

-- 
Best regards,
Vladimir

Re: [PATCH v4 2/3] vhost-user-blk: split vhost_user_blk_sync_config()

[Markus Armbruster]

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

> On 30.04.24 11:15, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
>> 
>>> Split vhost_user_blk_sync_config() out from
>>> vhost_user_blk_handle_config_change(), to be reused in the following
>>> commit.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>>> ---
>>>   hw/block/vhost-user-blk.c | 26 +++++++++++++++++++-------
>>>   1 file changed, 19 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
>>> index 9e6bbc6950..091d2c6acf 100644
>>> --- a/hw/block/vhost-user-blk.c
>>> +++ b/hw/block/vhost-user-blk.c
>>> @@ -88,27 +88,39 @@ static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
>>>       s->blkcfg.wce = blkcfg->wce;
>>>   }
>>>   +static int vhost_user_blk_sync_config(DeviceState *dev, Error **errp)
>>> +{
>>> +    int ret;
>>> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
>>
>> Note for later: all this function does with paramter @dev is cast it to
>> VirtIODevice *.
>> 
>>> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
>>> +
>>> +    ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
>>> +                               vdev->config_len, errp);
>>> +    if (ret < 0) {
>>> +        return ret;
>>> +    }
>>> +
>>> +    memcpy(vdev->config, &s->blkcfg, vdev->config_len);
>>> +    virtio_notify_config(vdev);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>>  static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
>>>  {
>>>      int ret;
>>> -    VirtIODevice *vdev = dev->vdev;
>>> -    VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
>>>      Error *local_err = NULL;
>>>
>>>      if (!dev->started) {
>>>          return 0;
>>>      }
>>>
>>> -    ret = vhost_dev_get_config(dev, (uint8_t *)&s->blkcfg,
>>> -                               vdev->config_len, &local_err);
>>> +    ret = vhost_user_blk_sync_config(DEVICE(dev->vdev), &local_err);
>>
>> dev->vdev is a VirtIODevice *.  You cast it to DeviceState * for
>> vhost_user_blk_sync_config(), which casts it right back.
>> Could you simply pass it as is instead?
>
> vhost_user_blk_sync_config() is generic handler, which will be used as ->sync_config() in the following commit, so it's good and convenient for it to have DeviceState* argument.

Ah, that's what I missed.

>>>      if (ret < 0) {
>>>          error_report_err(local_err);
>>>          return ret;
>>>      }
>>>
>>> -    memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
>>> -    virtio_notify_config(dev->vdev);
>>> -
>>>      return 0;
>>>  }

[PATCH v4 3/3] qapi: introduce device-sync-config

[Vladimir Sementsov-Ogievskiy]

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.
+# 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.
+     *
+     * Moreover, let's not rely on setting up interrupts in paused
+     * state, which may be a part of migration process.
+     */
+
+    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, "
+                   "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;
-- 
2.34.1

Re: [PATCH v4 3/3] qapi: introduce device-sync-config

[Markus Armbruster]

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?

> +     */
> +
> +    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;

Re: [PATCH v4 3/3] qapi: introduce device-sync-config

[Vladimir Sementsov-Ogievskiy]

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

Re: [PATCH v4 3/3] qapi: introduce device-sync-config

[Vladimir Sementsov-Ogievskiy]

On 30.04.24 11:31, Vladimir Sementsov-Ogievskiy wrote:
> 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.

Checked. Seems this works (in scheme pause -> migrate -> resume, interrupts are migrated and triggered on target after resume), so my doubt was wrong.

> 
>>
>>> +     */
>>> +
>>> +    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

Re: [PATCH v4 3/3] qapi: introduce device-sync-config

[Markus Armbruster]

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

> On 30.04.24 11:31, Vladimir Sementsov-Ogievskiy wrote:
>> 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>

[...]

>>>> 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.
>
> Checked. Seems this works (in scheme pause -> migrate -> resume, interrupts are migrated and triggered on target after resume), so my doubt was wrong.

Thanks!

[...]