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X-Received-From: 2a00:1450:4864:20::344 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: QEMU Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi On Sun, Dec 1, 2019 at 9:18 PM Peter Maydell wro= te: > > On Sun, 1 Dec 2019 at 10:19, Marc-Andr=C3=A9 Lureau > wrote: > > > > - "serial: register vmsd with DeviceClass" > > > > This is standard qdev-ification, however it breaks backward migration, > > but that's just how qdev_set_legacy_instance_id() works. > > I don't understand this part. Surely the whole point > of setting a legacy instance ID is exactly to preserve > migration compatibility? If it doesn't do that then what > does setting legacy ID value do? > It works in old->new direction only, because new code can match the legacy instance id. But when going from new->old, the legacy instance id is lost, as it uses new 0-based instance_id. This is just the way we have done so far, but I wish to be corrected if I am wrong. See the commit description for a bit more details. --=20 Marc-Andr=C3=A9 Lureau