Re: [PATCH] virtio-blk: drop deprecated scsi=on|off property
On Tue, May 04, 2021 at 03:32:55PM +0100, Stefan Hajnoczi wrote:
On Thu, Apr 29, 2021 at 02:03:52PM -0400, Eduardo Habkost wrote:
> On Thu, Apr 29, 2021 at 04:52:21PM +0100, Stefan Hajnoczi wrote:
> > Live migrating old guests from an old QEMU with the SCSI feature bit
> > enabled will fail with "Features 0x... unsupported. Allowed features:
> > 0x...". We've followed the QEMU deprecation policy so users have been
> > warned...
> >
>
> Were they really warned, though? People running
> "-machine pc-i440fx-2.4" might be completely unaware that it was
> silently enabling a deprecated feature.
>
> Can we have this documented in a more explicit way? Maybe just a
> comment at hw_compat_2_4 would be enough, to warn people doing
> backports and rebases downstream.
>
> Can we make QEMU refuse to start if using pc-2.4 + virtio-blk
> together, just to be sure?
On second thought, do we really want to break pc-2.4 user's QEMU
command-lines if they have a virtio-blk device?
It depends which command line you are talking about.
I believe we _must_ break the following:
"-machine pc-i440fx-2.4 -device virtio-blk", and
"-machine pc-i440fx-2.4 -device virtio-blk,scsi=on".
Your patch breaks only the latter.
Your patch also breaks the following:
"-machine pc-i440fx-2.4 -device virtio-blk,scsi=off",
which I don't think we should break.
BTW Peter mentioned libvirt avoids the unnecessary scsi=off:
https://gitlab.com/libvirt/libvirt/-/commit/ec69f0190be731d12faeac08dbf63...
Stefan
--
Eduardo