> -----Original Message----- > From: Jason Gunthorpe [mailto:jgg@xxxxxxxxxx] > Sent: 03 March 2022 13:20 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > linux-crypto@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; > alex.williamson@xxxxxxxxxx; cohuck@xxxxxxxxxx; mgurtovoy@xxxxxxxxxx; > yishaih@xxxxxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx>; liulongfang > <liulongfang@xxxxxxxxxx>; Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; > Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>; Wangzhou (B) > <wangzhou1@xxxxxxxxxxxxx> > Subject: Re: [PATCH v7 09/10] hisi_acc_vfio_pci: Add support for VFIO live > migration > > On Thu, Mar 03, 2022 at 01:17:05PM +0000, Shameerali Kolothum Thodi > wrote: > > > Tthere is a scenario that transfers only QM_MATCH_SIZE in stop_copy? > > > This doesn't seem like a good idea, I think you should transfer a > > > positive indication 'this device is not ready' instead of truncating > > > the stream. A truncated stream should not be a valid stream. > > > > > > ie always transfer the whole struct. > > > > We could add a 'qm_state' and return the whole struct. But the rest > > of the struct is basically invalid if qm_state = QM_NOT_REDAY. > > This seems like the right thing to do to me > > > > > Looks like setting the total_length = 0 in STOP_COPY is a better > > > > solution(If there are no other issues with that) as it will avoid > > > > grabbing the state_mutex as you mentioned above. > > > > > > That seems really weird, I wouldn't recommend doing that.. > > > > Does that mean we don't support a zero data transfer in STOP_COPY? > > total_length should not go backwards > > > The concern is if we always transfer the whole struct, we end up reading > > and writing the whole thing even if most of the data is invalid. > > Well, you can't know if the device is not ready or not until the > reaching STOP_COPY, so you have to transfer something to avoid > truncating the data stream. The state here is tiny, is the extra > transfer a real worry? Ok, don't think so. I will introduce the 'qm_state' and handle it as discussed above then. Thanks, Shameer
