From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cornelia Huck Subject: Re: [PATCH v3 1/9] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem Date: Thu, 14 Feb 2019 16:40:44 +0100 Message-ID: <20190214164044.5e67660a.cohuck@redhat.com> References: <1550152269-6317-1-git-send-email-pmorel@linux.ibm.com> <1550152269-6317-2-git-send-email-pmorel@linux.ibm.com> <20190214155441.087d2a68.cohuck@redhat.com> <6147f1ce-fd8b-1ec2-30ce-7ac68f3d8e27@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Pierre Morel , alex.williamson@redhat.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, frankja@linux.ibm.com, akrowiak@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, freude@linux.ibm.com, mimu@linux.ibm.com To: Christian Borntraeger Return-path: In-Reply-To: <6147f1ce-fd8b-1ec2-30ce-7ac68f3d8e27@de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, 14 Feb 2019 16:05:35 +0100 Christian Borntraeger wrote: > On 14.02.2019 15:54, Cornelia Huck wrote: > > On Thu, 14 Feb 2019 14:51:01 +0100 > > Pierre Morel wrote: > > Pierre, > this is independent from this series and should have been sent separately. > In the end (when we have the final solution) this will require cc stable. > > > >> Libudev relies on having a subsystem link for non-root devices. To > >> avoid libudev (and potentially other userspace tools) choking on the > >> matrix device let us introduce a vfio_ap bus and with that the vfio_ap > >> bus subsytem, and make the matrix device reside within it. > > > > How does libudev choke on this? It feels wrong to introduce a bus that > > basically does nothing... > > I have seen libvirt looping when a matrix device was available before the > libvirt start. > Marc Hartmayer debugged this and circumvented this in libvirt: > https://www.redhat.com/archives/libvir-list/2019-February/msg00837.html > > Still libudev expects a subsystem link in the matrix folder when doing the > udev_enumerate_scan_devices call. > > Having a bus is one way of adding a subsystem link. Ugh, that feels really broken. Adding a bus is probably the easiest way to get this working, though :/