[libvirt] [Question] nodedev-list --cap return nothing after creating a mdev

[Wuzongyong (Euler Dept)]

Hi,

I meet a problem that libvirt handle new mediated devices wrongly.
Command `virsh nodedev-list -cap mdev` return none after I create a mdev, and the root cause I found is:

// kernel code
int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid)
{
...
      ret = device_register(&mdev->dev); // send udev event here --- 1
      if (ret) {
            put_device(&mdev->dev);
            goto create_err;
      }

      ret = mdev_device_create_ops(kobj, mdev);
      if (ret)
            goto create_failed;

      ret = mdev_create_sysfs_files(&mdev->dev, type); // create mdev_type symbol link here --- 2
      if (ret) {
            mdev_device_remove_ops(mdev, true);
            goto create_failed;
      }

      mdev->type_kobj = kobj;
      dev_dbg(&mdev->dev, "MDEV: created\n");
...
}

At point 1, kernel send a udev event(add). If libvirt receive this event and handle it before kernel code reach point 2, libvirt
just fail to resolve link such as '/sys/devices/pci0000:80/0000:80:02.0/0000:81:00.0/36b79575-ada8-4406-893d-8cfd8d10a984/mdev_type'
because the link haven't been created yet. Then libvirt thinks this devices doesn't exsit and stop tracking info of this device.
Finally, command `vish nodedev-list -cap` return nothing though the device exist at host indeed.

To make it easy to reproduce this problem, I just add a `udelay(1)` before point 2 by kprobe.

So I think maybe we should add 'kobject_uevent(..., KOBJ_ADD)' after point 2 instead of point 1 ?
Or is there any other method to solve this problem?



Thanks,
Zongyong Wu

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