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envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.422, 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, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Mar 19, 2024 at 07:52:47PM +0000, Daniel P. Berrangé wrote: > On Tue, Mar 19, 2024 at 03:25:18PM -0400, Peter Xu wrote: > > On Tue, Mar 19, 2024 at 04:25:32PM +0000, Daniel P. Berrangé wrote: > > > On Fri, Mar 15, 2024 at 04:54:27PM -0400, Peter Xu wrote: > > > > On Fri, Mar 15, 2024 at 03:01:09PM -0300, Fabiano Rosas wrote: > > > > > Peter Xu writes: > > > > > > > > > > > [I queued patch 1-2 into -stable, leaving this patch for further > > > > > > discussions] > > > > > > > > > > > > On Fri, Mar 15, 2024 at 08:55:42AM +0000, Daniel P. Berrangé wrote: > > > > > >> The 'file:' protocol eventually calls into qemu_open, and this > > > > > >> transparently allows for FD passing using /dev/fdset/NNN syntax > > > > > >> to pass in FDs. > > > > > > > > > > > > If it always use /dev/fdsets for files, does it mean that the newly added > > > > > > SOCKET_ADDRESS_TYPE_FD support on mapped-ram will never be used (so we can > > > > > > drop them)? > > > > > > > > > > We already have SOCKET_ADDRESS_TYPE_FD + file since 8.2 when the > > > > > MigrationAddress was added. So this: > > > > > > > > > > 'channels': [ { 'channel-type': 'main', > > > > > 'addr': { 'transport': 'socket', > > > > > 'type': 'fd', > > > > > 'str': 'fdname' } } ] > > > > > > > > > > works without multifd and without mapped-ram if the fd is a file or > > > > > socket. > > > > > > > > > > So yes, you're correct, but given we already have this^ it would be > > > > > perhaps more confusing for users to allow it, but not allow the very > > > > > same JSON when multifd=true, mapped-ram=true. > > > > > > > > I don't think the fd: protocol (no matter the old "fd:", or the new JSON > > > > format) is trivial to use. If libvirt didn't use it I won't be surprised to > > > > see nobody using it. I want us to avoid working on things that nobody is > > > > using, or has a better replacement. > > > > > > > > So even if Libvirt supports both, I'm wondering whether /dev/fdset/ works > > > > for all the cases that libvirt needs. I am aware that the old getfd has > > > > the monitor limitation so that if the QMP disconnected and reconnect, the > > > > fd can be gone. However I'm not sure whether that's the only reason to > > > > have add-fd, and also not sure whether it means add-fd is always preferred, > > > > so that maybe we can consider obsolete getfd? > > > > > > Historically libvirt primariily uses the 'fd:' protocol, with a > > > socket FD. It never gives QEMU a plain file FD, since it has > > > always added its "iohelper" as a MITM, in order to add O_DIRECT > > > on top. > > > > > > The 'getfd' command is something that is needed when talking to > > > QEMU for any API that involves a "SocketAddress" QAPI type, > > > which is applicable for migration. > > > > > > With the introduction of 'MigrationAddress', the 'socket' protocol > > > is backed by 'SocketAddress' and thus supports FD passing for > > > sockets (or potentally pipes too), in combination with 'getfd'. > > > > > > With the 'file' protocol in 'MigrationAddress', since it gets > > > backed by qemu_open(), then /dev/fdset/NN and 'add-fd' provide > > > passing for plain files. > > > > I see. I assume it means we still have multiple users of getfd so it's > > still in use where add-fd is not yet avaiable. > > > > But then, SOCKET_ADDRESS_TYPE_FD is then not used for libvirt in the whole > > mapped-ram effort, neither do we need any support on file migrations over > > "fd", e.g. fd_start_incoming_migration() for files. So we can drop these > > parts, am I right? > > Correct, libvirt hasn't got any impl for 'mapped-ram' yet, at least > not something merged. > > Since this is new functionality, libvirt could go straight for the > 'file' protocol / address type. > > At some point I think we can stop using 'fd' for traditional migration > too and pass the socket address to QEMU and let QEMU open the socket. Thanks for confirming this, that sounds good. I quickly discussed this with Fabiano just now, I think there's a plan we start to mark fd migration deprecated for the next release (9.1), then there is a chance we drop it in migration for 9.3. That'll copy libvirt list so we can re-check there. Fabiano will then prepare patches to remove the "fd:" support on file migrations; that will be for 9.0. Thanks, -- Peter Xu