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

On Thu, Apr 29, 2021 at 04:52:21PM +0100, Stefan Hajnoczi wrote: > The scsi=on|off property was deprecated in QEMU 5.0 and can be removed > completely at this point. > > Drop the scsi=on|off option. It was only available on Legacy virtio-blk > devices. Linux v5.6 already dropped support for it. > > Remove the hw_compat_2_4[] property assignment since scsi=on|off no > longer exists. Old guests with Legacy virtio-blk devices no longer see > the SCSI host features bit. > This means pc-2.4 will now break guest ABI if using virtio-blk devices, correct?

> 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? An alternative would be keeping the property (and the hw_compat_2_4 entry) just to keep pc-2.4 working (until pc-2.4 is deprecated and removed), but refusing to realize the device if the feature is enabled.