From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39644) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVflr-0001mK-Qk for qemu-devel@nongnu.org; Thu, 13 Jul 2017 11:11:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVfln-0003rp-M6 for qemu-devel@nongnu.org; Thu, 13 Jul 2017 11:11:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37728) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVfln-0003rM-DD for qemu-devel@nongnu.org; Thu, 13 Jul 2017 11:11:11 -0400 Date: Thu, 13 Jul 2017 16:11:05 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170713151104.GE2121@work-vm> References: <1499942429-55449-1-git-send-email-borntraeger@de.ibm.com> <1499942429-55449-4-git-send-email-borntraeger@de.ibm.com> <20170713142721.3a40e083@gondolin> <1798a9f2-63f0-ab03-11ad-5513d9a90da9@linux.vnet.ibm.com> <20170713144941.GD2121@work-vm> <99be1408-f8e4-7ecb-f47e-9de94a20ff18@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <99be1408-f8e4-7ecb-f47e-9de94a20ff18@de.ibm.com> Subject: Re: [Qemu-devel] [PATCH/s390-next 3/3] s390x/flic: migrate ais states List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger Cc: Halil Pasic , Cornelia Huck , Juan Quintela , Yi Min Zhao , Pierre Morel , qemu-devel , Alexander Graf , Thomas Huth , Richard Henderson * Christian Borntraeger (borntraeger@de.ibm.com) wrote: > On 07/13/2017 04:49 PM, Dr. David Alan Gilbert wrote: > > * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > >> > >> > >> On 07/13/2017 02:27 PM, Cornelia Huck wrote: > >>>> +static void kvm_flic_ais_pre_save(void *opaque) > >>>> +{ > >>>> + KVMS390FLICStateMigTmp *tmp = opaque; > >>>> + KVMS390FLICState *flic = tmp->parent; > >>>> + struct kvm_s390_ais_all ais; > >>>> + struct kvm_device_attr attr = { > >>>> + .group = KVM_DEV_FLIC_AISM_ALL, > >>>> + .addr = (uint64_t)&ais, > >>>> + .attr = sizeof(ais), > >>>> + }; > >>>> + > >>>> + if (ioctl(flic->fd, KVM_GET_DEVICE_ATTR, &attr)) { > >>>> + error_report("Failed to retrieve kvm flic ais states"); > >>> There's not much else we can do in that case, is there? > >>> > >> > >> I think this is a very good question! The ioctl should not fail > >> under any circumstances, but if it does we have a problem. > >> > >> Carrying on happily (what we do now) means effectively discarding > >> ais state. In general just discarding state ain't a good idea. > >> > >> In particular it might be OK, but the patch should explain that! > >> > >> Regarding what could/should we do in such a case (instead > >> of discarding state and carrying on happily) I don't know, so > >> I tend to agree with you regarding 'not much else we can do'. > >> > >> Adding Dave and Juan. Maybe they can tell. > > > > I keep meaning to make the pre_save give a return value for failure, > > but it hasn't currently got one. > > Would you accept patches for that? Sure. > > > > You could try something like: > > > > qemu_file_set_error(migrate_get_current()->to_dst_file, -EINVAL); > > > > I *think* the migration code should spot that before it finishes > > but it might carry on for a little while before it does. > > I will keep this patch as is, since this is one of the "should not happen" > cases. And you've got a log message, so when the impossible happens at least we should be able to debug it. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK