On 9/12/2016 10:40 AM, Jike Song wrote:
> On 09/10/2016 03:55 AM, Kirti Wankhede wrote:
>> On 9/10/2016 12:12 AM, Alex Williamson wrote:
>>> On Fri, 9 Sep 2016 23:18:45 +0530
>>> Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
>>>
>>>> On 9/8/2016 1:39 PM, Jike Song wrote:
>>>>> On 08/25/2016 11:53 AM, Kirti Wankhede wrote:
>>>>
>>>>>> +---------------+
>>>>>> | |
>>>>>> | +-----------+ | mdev_register_driver() +--------------+
>>>>>> | | | +<------------------------+ __init() |
>>>>>> | | mdev | | | |
>>>>>> | | bus | +------------------------>+ |<-> VFIO user
>>>>>> | | driver | | probe()/remove() | vfio_mdev.ko | APIs
>>>>>> | | | | | |
>>>>>> | +-----------+ | +--------------+
>>>>>> | |
>>>>>
>>>>> This aimed to have only one single vfio bus driver for all mediated devices,
>>>>> right?
>>>>>
>>>>
>>>> Yes. That's correct.
>>>>
>>>>
>>>>>> +
>>>>>> +static int mdev_add_attribute_group(struct device *dev,
>>>>>> + const struct attribute_group **groups)
>>>>>> +{
>>>>>> + return sysfs_create_groups(&dev->kobj, groups);
>>>>>> +}
>>>>>> +
>>>>>> +static void mdev_remove_attribute_group(struct device *dev,
>>>>>> + const struct attribute_group **groups)
>>>>>> +{
>>>>>> + sysfs_remove_groups(&dev->kobj, groups);
>>>>>> +}
>>>>>
>>>>> These functions are not necessary. You can always specify the attribute groups
>>>>> to dev->groups before registering a new device.
>>>>>
>>>>
>>>> At the time of mdev device create, I specifically didn't used
>>>> dev->groups because we callback in vendor driver before that, see below
>>>> code snippet, and those attributes should only be added if create()
>>>> callback returns success.
>>>>
>>>> ret = parent->ops->create(mdev, mdev_params);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> ret = mdev_add_attribute_group(&mdev->dev,
>>>> parent->ops->mdev_attr_groups);
>>>> if (ret)
>>>> parent->ops->destroy(mdev);
>>>>
>>>>
>>>>
>>>>>> +
>>>>>> +static struct parent_device *mdev_get_parent_from_dev(struct device *dev)
>>>>>> +{
>>>>>> + struct parent_device *parent;
>>>>>> +
>>>>>> + mutex_lock(&parent_list_lock);
>>>>>> + parent = mdev_get_parent(__find_parent_device(dev));
>>>>>> + mutex_unlock(&parent_list_lock);
>>>>>> +
>>>>>> + return parent;
>>>>>> +}
>>>>>
>>>>> As we have demonstrated, all these refs and locks and release workqueue are not necessary,
>>>>> as long as you have an independent device associated with the mdev host device
>>>>> ("parent" device here).
>>>>>
>>>>
>>>> I don't think every lock will go away with that. This also changes how
>>>> mdev devices entries are created in sysfs. It adds an extra directory.
>>>
>>> Exposing the parent-child relationship through sysfs is a desirable
>>> feature, so I'm not sure how this is a negative. This part of Jike's
>>> conversion was a big improvement, I thought. Thanks,
>>>
>>
>> Jike's suggestion is to introduced a fake device over parent device i.e.
>> mdev-host, and then all mdev devices are children of 'mdev-host' not
>> children of real parent.
>>
>
> It really depends on how you define 'real parent' :)
>
> With a physical-host-mdev hierarchy, the parent of mdev devices is the host
> device, the parent of host device is the physical device. e.g.
>
> pdev mdev_host mdev_device
> dev<------------dev<------------dev
> parent parent
>
> Figure 1: device hierarchy
>
Right, mdev-host device doesn't represent physical device nor any mdev
device. Then what is the need of such device?
>> For example, directory structure we have now is:
>> /sys/bus/pci/devices/0000\:85\:00.0/<mdev_device>
>>
>> mdev devices are in real parents directory.
>>
>> By introducing fake device it would be:
>> /sys/bus/pci/devices/0000\:85\:00.0/mdev-host/<mdev_device>
>>
>> mdev devices are in fake device's directory.
>>
>
> Yes, this is the wanted directory.
>
I don't think so.
>> Lock would be still required, to handle the race conditions like
>> 'mdev_create' is still in process and parent device is unregistered by
>> vendor driver/ parent device is unbind from vendor driver.
>>
>
> locks are provided to protect resources, would you elaborate more on
> what is the exact resource you want to protect by a lock in mdev_create?
>
Simple, in your suggestion mdev-host device. Fake device will go away if
vendor driver unregisters the device from mdev module, right.
Thanks,
Kirti.
>> With the new changes/discussion, we believe the locking will be
>> simplified without having fake parent device.
>>
>> With fake device suggestion, removed pointer to parent device from
>> mdev_device structure. When a create(struct mdev_device *mdev) callback
>> comes to vendor driver, how would vendor driver know for which physical
>> device this mdev device create call is intended to? because then
>> 'parent' would be newly introduced fake device, not the real parent.
>
> Please have a look at "Figure 1".
>
> --
> Thanks,
> Jike
>
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