Re: [PATCH v8 02/17] qdev: unplug blocker for devices

[Jag Raman]

> On Apr 21, 2022, at 10:55 AM, Markus Armbruster <armbru@redhat.com> wrote:
> 
> Jagannathan Raman <jag.raman@oracle.com> writes:
> 
>> Add blocker to prevent hot-unplug of devices
> 
> Why do you need this?  I'm not doubting you do, I just want to read your
> reasons here :)

Hi Markus, :)

The x-vfio-user-server depends on an attached PCIDevice. As long as 
x-vfio-user-server
is used, we don’t want the PCIDevice to be unplugged. This blocker prevents an 
user
from removing PCIDevice while the vfio-user server is in use.

> 
>> 
>> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
>> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
>> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>

I recall receiving a “Reviewed-by” from Stefan previously.

I’m very sorry I didn’t add that here. I’ll go over all the patches once again 
to confirm that
the “Reviewed-by” status reflects accurately.

>> ---
>> include/hw/qdev-core.h | 29 +++++++++++++++++++++++++++++
>> hw/core/qdev.c         | 24 ++++++++++++++++++++++++
>> softmmu/qdev-monitor.c |  4 ++++
>> 3 files changed, 57 insertions(+)
>> 
>> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
>> index 92c3d65208..1b9fa25e5c 100644
>> --- a/include/hw/qdev-core.h
>> +++ b/include/hw/qdev-core.h
>> @@ -193,6 +193,7 @@ struct DeviceState {
>>     int instance_id_alias;
>>     int alias_required_for_version;
>>     ResettableState reset;
>> +    GSList *unplug_blockers;
>> };
>> 
>> struct DeviceListener {
>> @@ -419,6 +420,34 @@ void qdev_simple_device_unplug_cb(HotplugHandler 
>> *hotplug_dev,
>> void qdev_machine_creation_done(void);
>> bool qdev_machine_modified(void);
>> 
>> +/*
>> + * qdev_add_unplug_blocker: Adds an unplug blocker to a device
>> + *
>> + * @dev: Device to be blocked from unplug
>> + * @reason: Reason for blocking
>> + */
>> +void qdev_add_unplug_blocker(DeviceState *dev, Error *reason);
>> +
>> +/*
>> + * qdev_del_unplug_blocker: Removes an unplug blocker from a device
>> + *
>> + * @dev: Device to be unblocked
>> + * @reason: Pointer to the Error used with qdev_add_unplug_blocker.
>> + *          Used as a handle to lookup the blocker for deletion.
>> + */
>> +void qdev_del_unplug_blocker(DeviceState *dev, Error *reason);
>> +
>> +/*
>> + * qdev_unplug_blocked: Confirms if a device is blocked from unplug
>> + *
>> + * @dev: Device to be tested
>> + * @reason: Returns one of the reasons why the device is blocked,
>> + *          if any
>> + *
>> + * Returns: true if device is blocked from unplug, false otherwise
>> + */
>> +bool qdev_unplug_blocked(DeviceState *dev, Error **errp);
>> +
>> /**
>>  * GpioPolarity: Polarity of a GPIO line
>>  *
>> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
>> index 84f3019440..0806d8fcaa 100644
>> --- a/hw/core/qdev.c
>> +++ b/hw/core/qdev.c
>> @@ -468,6 +468,28 @@ char *qdev_get_dev_path(DeviceState *dev)
>>     return NULL;
>> }
>> 
>> +void qdev_add_unplug_blocker(DeviceState *dev, Error *reason)
>> +{
>> +    dev->unplug_blockers = g_slist_prepend(dev->unplug_blockers, reason);
>> +}
>> +
>> +void qdev_del_unplug_blocker(DeviceState *dev, Error *reason)
>> +{
>> +    dev->unplug_blockers = g_slist_remove(dev->unplug_blockers, reason);
>> +}
>> +
>> +bool qdev_unplug_blocked(DeviceState *dev, Error **errp)
>> +{
>> +    ERRP_GUARD();
>> +
>> +    if (dev->unplug_blockers) {
>> +        error_propagate(errp, error_copy(dev->unplug_blockers->data));
>> +        return true;
>> +    }
>> +
>> +    return false;
>> +}
> 
> This cites the most recently added blocker as reason.  Your function
> comment covers it: "Returns one of the reasons".  Okay.

I could change the comment to say that it returns the recently added reason.

Thank you!
--
Jag

> 
>> +
>> static bool device_get_realized(Object *obj, Error **errp)
>> {
>>     DeviceState *dev = DEVICE(obj);
>> @@ -704,6 +726,8 @@ static void device_finalize(Object *obj)
>> 
>>     DeviceState *dev = DEVICE(obj);
>> 
>> +    g_assert(!dev->unplug_blockers);
>> +
>>     QLIST_FOREACH_SAFE(ngl, &dev->gpios, node, next) {
>>         QLIST_REMOVE(ngl, node);
>>         qemu_free_irqs(ngl->in, ngl->num_in);
>> diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
>> index 12fe60c467..9cfd59d17c 100644
>> --- a/softmmu/qdev-monitor.c
>> +++ b/softmmu/qdev-monitor.c
>> @@ -898,6 +898,10 @@ void qdev_unplug(DeviceState *dev, Error **errp)
>>     HotplugHandlerClass *hdc;
>>     Error *local_err = NULL;
>> 
>> +    if (qdev_unplug_blocked(dev, errp)) {
>> +        return;
>> +    }
>> +
>>     if (dev->parent_bus && !qbus_is_hotpluggable(dev->parent_bus)) {
>>         error_setg(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
>>         return;
>