From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com ([207.211.31.81]:53496 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726127AbgD3Kn0 (ORCPT ); Thu, 30 Apr 2020 06:43:26 -0400 Date: Thu, 30 Apr 2020 12:43:16 +0200 From: Cornelia Huck Subject: Re: [RFD] uevent handling for subchannels Message-ID: <20200430124316.023a82b0.cohuck@redhat.com> In-Reply-To: <53d7d08d-c1d2-dad3-7f01-a165b24b0359@linux.ibm.com> References: <20200403124032.5e70603d.cohuck@redhat.com> <20200417143811.7e6ecb2c.cohuck@redhat.com> <8649ea94-8617-07b6-170e-65c278d9383b@linux.vnet.ibm.com> <20200423182001.40345df8.cohuck@redhat.com> <53d7d08d-c1d2-dad3-7f01-a165b24b0359@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Peter Oberparleiter Cc: Vineeth Vijayan , Vineeth Vijayan , linux-s390@vger.kernel.org, Eric Farman , Halil Pasic , Boris Fiuczynski On Mon, 27 Apr 2020 12:10:17 +0200 Peter Oberparleiter wrote: > On 23.04.2020 18:20, Cornelia Huck wrote: > > On Thu, 23 Apr 2020 16:52:24 +0200 > > Vineeth Vijayan wrote: > >> Then we could also change the way ccw_device_call_sch_unregister() > >> works, where > >> the subchannel-unregister is happening from an upper layer. > > > > Hm, what's the problem here? This seems to be mostly a case of "we did > > I/O to the device and it appeared not operational; so we go ahead and > > unregister the subchannel"? Childless I/O subchannels are a bit useless. > > Hey Conny, > > sparked by your proposal, Vineeth and myself looked at the corresponding > CIO code and wondered if things couldn't be done in a generally > better/cleaner way. So here we'd like to get your opinion. > > In particular, as it is currently, a child-driver (IO subchannel driver, > vfio-ccw, etc.) unregisters a device owned by a parent-device-driver > (CSS), which feels from a high-level-view like a layering violation: > only the parent driver should register and unregister the parent device. > Also in case no subchannel driver is available (e.g. due to > driver_override=none), there would be no subchannel ADD event at all. Doesn't the base css code generate the uevent in that case? > > So, tapping into you historical expertise about CIO, is there any reason > for doing it this way beyond being nice to userspace tooling that > subchannels with non-working CCW devices are automatically hidden by > unregistering them? We always had ccw devices behind I/O subchannels, but that has not been the case since we introduced vfio-ccw, so hopefully everybody can deal with that. The rationale behind this was that device-less I/O subchannels were deemed to be useless; I currently can't remember another reason. What about EADM, btw? CHSC does not have a device, and message does not have a driver. > > Removing the child-unregisters-parent logic this would also enable > manual rebind of subchannels for which only a different driver than the > default one can successfully talk to the child device, though I'm > unaware of any current application for that. Yes. Let me think about that some more (no clear head currently, sorry.)