On 20/09/2016 14:39, Pavel Dovgalyuk wrote:
> > > + replay_snapshot = g_strdup(qemu_opt_get(opts, "rrsnapshot"));
> > > +
> > > replay_enable(fname, mode);
> > >
> >
> > Should you set snapshot = 1 here if there is no rrsnapshot option?
>
> No, because there is default snapshot name for the case when user
> specifies overlay for the drives.
There are three possibilities:
a) these patches:
with implicit overlay:
-drive file=disk.raw,if=none,id=img-direct
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
with explicit overlay:
-drive file=disk.raw,if=none,id=img-direct
-drive
driver=blkreplay,if=none,image=img-direct,id=img-blkreplay,overlay=foo.qcow2
Advantages:
- does the right thing in the "implicit overlay" case.
Disadvantages:
- no need really to specify disk.raw in the "explicit overlay" case, since
it's already specified when you create the overlay with qemu-img.
Vote for implicit overlay: excellent
Vote for explicit overlay: bad (need to track two file names)
b) always specify -snapshot manually:
with implicit overlay:
-drive file=disk.raw,if=none,id=img-direct -snapshot
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
with explicit overlay:
-drive file=foo.qcow2,if=none,id=img-direct
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
Advantages:
- can use default snapshot name in the "explicit overlay" case
Disadvantages:
- need to specify -snapshot explicitly for the "implicit overlay" case
Vote for implicit overlay: awful (disk.raw destroy if you forget -snapshot)
Vote for explicit overlay: excellent
c) no rrsnapshot implies -snapshot:
without overlay:
-drive file=disk.raw,if=none,id=img-direct
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
with overlay:
-drive file=foo.qcow2,if=none,id=img-direct
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
-icount ...,rrsnapshot=snapname
Advantages:
- does the right thing in the "implicit overlay" case.
Disadvantages:
- always have to specify snapshot name in the "explicit overlay" case
Vote for implicit overlay: excellent (same as a)
Vote for explicit overlay: decent
We have to choose between (a) and (c) I think, because the risk of corruption
for (b) is too high. I prefer (c). Kevin, what do you think?
Thanks,
Paolo
