[PATCH] virtio-blk: drop deprecated scsi=on|off property

[Eduardo Habkost]

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/ec69f0190be731d12faeac08dbf63325836509a9
> 
> Stefan



-- 
Eduardo