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

[Peter Krempa <pkrempa@redhat.com>]

On Thu, Apr 29, 2021 at 16:52:21 +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.

Does this mean that qemu rejects it if it's explicitly enabled on the
commandline? 

> 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...
> 
> I have tested that libvirt still works when the property is absent. It
> no longer adds scsi=on|off to the command-line.

Yup, we deliberately don't format it unless the user requested it since:

https://gitlab.com/libvirt/libvirt/-/commit/ec69f0190be731d12faeac08dbf63325836509a9

Depending on your answer above I might need to dig through the code
again to see whether we do the correct thing if it's no longer
available.

> 
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Peter Krempa <pkrempa@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  docs/specs/tpm.rst           |   2 +-
>  docs/system/deprecated.rst   |  13 ---
>  docs/pci_expander_bridge.txt |   2 +-
>  hw/block/virtio-blk.c        | 192 +----------------------------------
>  hw/core/machine.c            |   2 -
>  5 files changed, 3 insertions(+), 208 deletions(-)