> From: Paolo Bonzini [mailto:paolo.bonz...@gmail.com] On Behalf Of Paolo > Bonzini > On 16/09/2016 09:55, Pavel Dovgalyuk wrote: > >> Since you have to create > >> overlay.qcow2 outside QEMU anyway, overlay.qcow2 might as well be the > >> "image". That is, you could choose between: > >> > >> -drive driver=blkreplay,if=none,image=overlay.qcow2,id=img-blkreplay \ > >> -rr snapshot=replay_init,... > >> > >> -drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay > >> > >> The temporary snapshot would be created if there's no "-rr snapshot" option > >> on the command line. > >> > >> Does this make sense? > > > > There are two different parts: > > - creating an overlay > > - creating the snapshot > > > > Overlay is needed to preserve the state of the original backing file. > > In the current version temporary overlay is always created at start of qemu. > > Yes, this would still be the default for rr mode. > > > I don't think that it is convenient forcing user to create overlay manually. > > Note that all I'm only saying that _only for the case where the user > creates the overlay manually anyway_ there is no need to specify both > image and overlay. (I also don't like particularly the hard-coded > snapshot name replay_init, which can be overridden by -loadvm but not > when saving).
Ok, this seems reasonable to fix. > > So there are various possibilites: > > First proposal: > > - automatically created overlay is -icount rr=record|replay (then > snapshot name doesn't matter, it can be replay_init) > > - manually created overlay is -icount > rr=record|replay,rrsnapshot=snapname (then snapshot name matters because > you can have different snapshots in the same file) We can't create overlay with icount suboptions, because there could be several block devices. Each one needs its own overlay. > If rr is enabled but rrsnapshot is absent, configure_icount can just set > "snapshot = 1" to force creation of the temporary overlay. This > requires no change to the blkreplay driver > > > Second proposal: > > - automatically created overlay is -icount rr=record|replay -snapshot > > - manually created overlay is -icount rr=record|replay and an rrsnapshot > suboption can be added anyway if considered useful. See above. > This requires no change to the blkreplay driver either. It's a little > more verbose in the common case, but perhaps less surprising if you're > already used to -snapshot. Our internal version automatically creates overlays with generated names. But now I think, that it is inconvenient and manual name specification is better. > > Common debugging scenario includes multiple recording passes until the bug > > manifests > > itself. Every new execution recorded should be accompanied by creating an > > overlay > > to assure that the execution is started from the same disk state. > > > > Specifying initial snapshot name makes sense if we want to suppress -loadvm > > option. > > My rationale was to have similar command lines between record and replay > modes (just changing rr=record to rr=replay). This seems reasonable, I'll try to fix this part. Pavel Dovgalyuk
