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

[Wuzongyong (Euler Dept)]

Hi,

I solve this problem by sending a CHANGE event to userspace after creating the symbol link like sriov driver.

diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index 1269910..a23f1d7 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -351,6 +351,8 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid)
                goto create_failed;
        }

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

Is this patch ok?

Thanks,
Zongyong Wu


> -----Original Message-----
> From: Erik Skultety [mailto:eskultet at redhat.com]
> Sent: Thursday, February 01, 2018 4:09 PM
> To: Wuzongyong (Euler Dept) <cordius.wu at huawei.com>
> Cc: Alex Williamson <alex.williamson at redhat.com>; libvir-list at redhat.com;
> weijinfen <weijinfen at huawei.com>
> Subject: Re: [libvirt][Question] nodedev-list --cap return nothing after
> creating a mdev
> 
> On Thu, Feb 01, 2018 at 07:19:45AM +0000, Wuzongyong (Euler Dept) wrote:
> > 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?
> 
> Hi,
> just a note, we worked around this in upstream libvirt already.
> 
> Thanks for the pointer though, I'd also be interested in possible
> solutions in kernel.
> 
> Erik