Re: -drive if=none: can't we make this the default?

[Kevin Wolf <kwolf@redhat.com>]

Am 02.11.2023 um 12:01 hat Peter Maydell geschrieben:
> On Thu, 2 Nov 2023 at 10:43, Kevin Wolf <kwolf@redhat.com> wrote:
> >
> > Am 01.11.2023 um 12:21 hat Peter Maydell geschrieben:
> > > On Tue, 31 Oct 2023 at 18:45, Kevin Wolf <kwolf@redhat.com> wrote:
> > > > Am 16.10.2023 um 13:58 hat Michael Tokarev geschrieben:
> > > > > Almost everyone mentions -blockdev as a replacement for -drive.
> > > >
> > > > More specifically for -drive if=none. I honestly don't know many common
> > > > use cases for that one.
> > >
> > > One use case for it is "create a drive with a qcow2 backend to use
> > > for -snapshot snapshots, but don't plug it into anything". See
> > > https://translatedcode.wordpress.com/2015/07/06/tricks-for-debugging-qemu-savevm-snapshots/
> > > I dunno whether that counts as "common", though :-)
> >
> > Ok, I was already wondering what good -snapshot was for an image that
> > isn't even used, but what the article describes is actually not using
> > -snapshot, but internal snapshots with savevm/loadvm, i.e. using the
> > image to store the VM state.
> >
> > This actually makes a lot of sense for if=none, as one of the few cases
> > where "none" accurately tells what device it will be used with.
> 
> Whoops, have I got the terminology wrong again? To me these are
> "snapshots" (they do store the whole VM state including the current
> state of the disk, and "qemu-img info" lists them as "snapshots"),
> whereas I never use the '-snapshot' option, so I never remember
> that we have two different things here. Sorry for introducing
> confusion :-(

It is confusing, -snapshot really doesn't have the best name.

But anyway, your case with savevm/loadvm should work fine with
-blockdev.

Kevin