On Fri, Dec 01, 2023 at 11:23:33AM -0500, Steven Sistare wrote: > >> @@ -109,6 +117,7 @@ static int global_state_post_load(void *opaque, int > >> version_id) > >> return -EINVAL; > >> } > >> s->state = r; > >> + vm_set_suspended(s->vm_was_suspended || r == RUN_STATE_SUSPENDED); > > > > IIUC current vm_was_suspended (based on my read of your patch) was not the > > same as a boolean representing "whether VM is suspended", but only a > > temporary field to remember that for a VM stop request. To be explicit, I > > didn't see this flag set in qemu_system_suspend() in your previous patch. > > > > If so, we can already do: > > > > vm_set_suspended(s->vm_was_suspended); > > > > Irrelevant of RUN_STATE_SUSPENDED? > > We need both terms of the expression. > > If the vm *is* suspended (RUN_STATE_SUSPENDED), then vm_was_suspended = false. > We call global_state_store prior to vm_stop_force_state, so the incoming > side sees s->state = RUN_STATE_SUSPENDED and s->vm_was_suspended = false.
Right. > However, the runstate is RUN_STATE_INMIGRATE. When incoming finishes by > calling vm_start, we need to restore the suspended state. Thus in > global_state_post_load, we must set vm_was_suspended = true. With above, shouldn't global_state_get_runstate() (on dest) fetch SUSPENDED already? Then I think it should call vm_start(SUSPENDED) if to start. Maybe you're talking about the special case where autostart==false? We used to have this (existing process_incoming_migration_bh()): if (!global_state_received() || global_state_get_runstate() == RUN_STATE_RUNNING) { if (autostart) { vm_start(); } else { runstate_set(RUN_STATE_PAUSED); } } If so maybe I get you, because in the "else" path we do seem to lose the SUSPENDED state again, but in that case IMHO we should logically set vm_was_suspended only when we "lose" it - we didn't lose it during migration, but only until we decided to switch to PAUSED (due to autostart==false). IOW, change above to something like: state = global_state_get_runstate(); if (!global_state_received() || runstate_is_alive(state)) { if (autostart) { vm_start(state); } else { if (runstate_is_suspended(state)) { /* Remember suspended state before setting system to STOPed */ vm_was_suspended = true; } runstate_set(RUN_STATE_PAUSED); } } It may or may not have a functional difference even if current patch, though. However maybe clearer to follow vm_was_suspended's strict definition. > > If the vm *was* suspended, but is currently stopped (eg RUN_STATE_PAUSED), > then vm_was_suspended = true. Migration from that state sets > vm_was_suspended = s->vm_was_suspended = true in global_state_post_load and > ends with runstate_set(RUN_STATE_PAUSED). > > I will add a comment here in the code. > > >> return 0; > >> } > >> @@ -134,6 +143,7 @@ static const VMStateDescription vmstate_globalstate = { > >> .fields = (VMStateField[]) { > >> VMSTATE_UINT32(size, GlobalState), > >> VMSTATE_BUFFER(runstate, GlobalState), > >> + VMSTATE_BOOL(vm_was_suspended, GlobalState), > >> VMSTATE_END_OF_LIST() > >> }, > >> }; > > > > I think this will break migration between old/new, unfortunately. And > > since the global state exist mostly for every VM, all VM setup should be > > affected, and over all archs. > > Thanks, I keep forgetting that my binary tricks are no good here. However, > I have one other trick up my sleeve, which is to store vm_was_running in > global_state.runstate[strlen(runstate) + 2]. It is forwards and backwards > compatible, since that byte is always 0 in older qemu. It can be implemented > with a few lines of code change confined to global_state.c, versus many lines > spread across files to do it the conventional way using a compat property and > a subsection. Sound OK? Tricky! But sounds okay to me. I think you're inventing some of your own way of being compatible, not relying on machine type as a benefit. If go this route please document clearly on the layout and also what it looked like in old binaries. I think maybe it'll be good to keep using strings, so in the new binaries we allow >1 strings, then we define properly on those strings (index 0: runstate, existed since start; index 2: suspended, perhaps using "1"/"0" to express, while 0x00 means old binary, etc.). I hope this trick will need less code than the subsection solution, otherwise I'd still consider going with that, which is the "common solution". Let's also see whether Juan/Fabiano/others has any opinions. -- Peter Xu