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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/22 00:54:46 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: cjia@nvidia.com, aik@ozlabs.ru, Zhengxiao.zx@alibaba-inc.com, shuangtai.tst@alibaba-inc.com, qemu-devel@nongnu.org, peterx@redhat.com, eauger@redhat.com, yi.l.liu@intel.com, quintela@redhat.com, ziye.yang@intel.com, armbru@redhat.com, mlevitsk@redhat.com, pasic@linux.ibm.com, felipe@nutanix.com, zhi.a.wang@intel.com, kevin.tian@intel.com, yan.y.zhao@intel.com, "Dr. David Alan Gilbert" , alex.williamson@redhat.com, changpeng.liu@intel.com, eskultet@redhat.com, Ken.Xue@amd.com, jonathan.davies@nutanix.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 21 Oct 2020 11:03:23 +0530 Kirti Wankhede wrote: > On 10/20/2020 4:21 PM, Cornelia Huck wrote: > > On Sun, 18 Oct 2020 01:54:56 +0530 > > Kirti Wankhede wrote: > > > >> On 9/29/2020 4:33 PM, Dr. David Alan Gilbert wrote: > >>> * Cornelia Huck (cohuck@redhat.com) wrote: > >>>> On Wed, 23 Sep 2020 04:54:07 +0530 > >>>> Kirti Wankhede wrote: > >>>>> +static void vfio_vmstate_change(void *opaque, int running, RunState state) > >>>>> +{ > >>>>> + VFIODevice *vbasedev = opaque; > >>>>> + > >>>>> + if ((vbasedev->vm_running != running)) { > >>>>> + int ret; > >>>>> + uint32_t value = 0, mask = 0; > >>>>> + > >>>>> + if (running) { > >>>>> + value = VFIO_DEVICE_STATE_RUNNING; > >>>>> + if (vbasedev->device_state & VFIO_DEVICE_STATE_RESUMING) { > >>>>> + mask = ~VFIO_DEVICE_STATE_RESUMING; > >>>> > >>>> I've been staring at this for some time and I think that the desired > >>>> result is > >>>> - set _RUNNING > >>>> - if _RESUMING was set, clear it, but leave the other bits intact > >> > >> Upto here, you're correct. > >> > >>>> - if _RESUMING was not set, clear everything previously set > >>>> This would really benefit from a comment (or am I the only one > >>>> struggling here?) > >>>> > >> > >> Here mask should be ~0. Correcting it. > > > > Hm, now I'm confused. With value == _RUNNING, ~_RUNNING and ~0 as mask > > should be equivalent, shouldn't they? > > > > I too got confused after reading your comment. > Lets walk through the device states and transitions can happen here: > > if running > - device state could be either _SAVING or _RESUMING or _STOP. Both > _SAVING and _RESUMING can't be set at a time, that is the error state. > _STOP means 0. > - Transition from _SAVING to _RUNNING can happen if there is migration > failure, in that case we have to clear _SAVING > - Transition from _RESUMING to _RUNNING can happen on resuming and we > have to clear _RESUMING. > - In both the above cases, we have to set _RUNNING and clear rest 2 bits. > Then: > mask = ~VFIO_DEVICE_STATE_MASK; > value = VFIO_DEVICE_STATE_RUNNING; ok > > if !running > - device state could be either _RUNNING or _SAVING|_RUNNING. Here we > have to reset running bit. > Then: > mask = ~VFIO_DEVICE_STATE_RUNNING; > value = 0; ok > > I'll add comment in the code above. That will help. I'm a bit worried though that all that reasoning which flags are set or cleared when is quite complex, and it's easy to make mistakes. Can we model this as a FSM, where an event (running state changes) transitions the device state from one state to another? I (personally) find FSMs easier to comprehend, but I'm not sure whether that change would be too invasive. If others can parse the state changes with that mask/value interface, I won't object to it. > > > >> > >> > >>>>> + } > >>>>> + } else { > >>>>> + mask = ~VFIO_DEVICE_STATE_RUNNING; > >>>>> + }