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/ec69f0190be731d12faeac08dbf63325...
Stefan
-- Eduardo