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

[Markus Armbruster]

Jag Raman <jag.raman@oracle.com> writes:

>> 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.

Please work that into your commit message.  Perhaps along the lines of

    One of the next commits will do <stuff>.  <badness> will happen when
    the PCI device is unplugged.  Create the means to prevent that.

>>> 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.

Up to you.