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

-----Original Message----- From: Erik Skultety [mailto:eskultet@redhat.com] Sent: Thursday, February 01, 2018 4:09 PM To: Wuzongyong (Euler Dept) <cordius.wu(a)huawei.com&gt; Cc: Alex Williamson <alex.williamson(a)redhat.com>; libvir-list(a)redhat.com; weijinfen <weijinfen(a)huawei.com&gt; 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