Re: [PATCH v2 05/11] qemu-options: finesse the recommendations around -blockdev

[Kevin Wolf <kwolf@redhat.com>]

Am 04.04.2023 um 17:07 hat Michael Tokarev geschrieben:
> 04.04.2023 16:57, Kevin Wolf пишет:
> > Let's not make the use of -drive look more advisable than it really is.
> > If you're writing a management tool/script and you're still using -drive
> > today, you're doing it wrong.
> 
> Kevin, maybe I'm wrong here, but what to do with the situation which
> started it all, -- with -snapshot?
> 
> If anything, I think there should be a bold note that -snapshot is
> broken by -blockdev.  Users are learning that the *hard* way, after
> losing their data..

Ah, I missed this context.

Maybe -snapshot should error out if -blockdev is in use. You'd generally
expect that either -blockdev is used primarily and snapshots are done
externally (if the command line is generated by some management tool),
or that -drive is used consistently (by a human who likes the
convenience). In both cases, we wouldn't hit the error path.

There may be some exceptional cases where you have both -drive and
-blockdev (maybe because a human users needs more control for one
specific disk). This is the case where you can get a nasty surprise and
that would error out. If you legitimately want the -drive images
snapshotted, but not the -blockdev ones, you can still use individual
'-drive snapshot=on' options instead of the global '-snapshot' (and the
error message should mention this).

Would you see any problems with such an approach?

Kevin