On 21 May 2018 at 15:34, Paolo Bonzini <pbonz...@redhat.com> wrote: > Why do the levels have to be migrated at all? It should be enough if > the IRQ level is either migrated manually, or restored (e.g. in > post_save callbacks) through other data that is migrated.
This is standard behaviour for devices: they track their inbound irq/gpio lines, and then that becomes internal state for them that must be migrated. If we didn't migrate the input line state, then after a migration the levels[] array would be all zeroes, and the next time a connected device signalled a high-to-low transition we'd take the output line low even if it should not be (because we'd have forgotten that some other input lines were high). In a different world, the state would be in the qemu_irq line itself (in the same way that in hardware signal lines are their own state), but we can't get there from here. thanks -- PMM
