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). 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) 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. 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. > 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). Paolo > Then replay may be started from any state without using -loadvm. > > Pavel Dovgalyuk > > >
