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?
This looks like a sign we should have deprecated pc-2.4 a long
time ago.
> 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.
> I have tested that libvirt still works when the property is absent. It
> no longer adds scsi=on|off to the command-line.
>
> Cc: Markus Armbruster <armbru@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Peter Krempa <pkrempa@xxxxxxxxxx>
> Cc: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> ---
[...]
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 40def78183..286f18ec6d 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -194,8 +194,6 @@ GlobalProperty hw_compat_2_5[] = {
> const size_t hw_compat_2_5_len = G_N_ELEMENTS(hw_compat_2_5);
>
> GlobalProperty hw_compat_2_4[] = {
> - /* Optional because the 'scsi' property is Linux-only */
> - { "virtio-blk-device", "scsi", "true", .optional = true },
> { "e1000", "extra_mac_registers", "off" },
> { "virtio-pci", "x-disable-pcie", "on" },
> { "virtio-pci", "migrate-extra", "off" },
--
Eduardo
