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Re: [Qemu-devel] [PATCH] hw: report invalid disable-legacy|modern usage

From: Eduardo Habkost
Subject: Re: [Qemu-devel] [PATCH] hw: report invalid disable-legacy|modern usage for virtio-1-only devs
Date: Mon, 28 Jan 2019 15:48:57 -0200
User-agent: Mutt/1.10.1 (2018-07-13)

On Fri, Jan 18, 2019 at 01:38:26PM +0000, Daniel P. Berrangé wrote:
> A number of virtio devices (gpu, crypto, mouse, keyboard, tablet) only
> support the virtio-1 (aka modern) mode. Currently if the user launches
> QEMU, setting those devices to enable legacy mode, QEMU will silently
> create them in modern mode, ignoring the user's (mistaken) request.
> This patch introduces proper data validation so that an attempt to
> configure a virtio-1-only devices in legacy mode gets reported as an
> error to the user.
> Checking this required introduction of a new field to explicitly track
> what operating model is to be used for a device, separately from the
> disable_modern and disable_legacy fields that record the user's
> requested configuration.
> Signed-off-by: Daniel P. Berrangé <address@hidden>

This breaks the virtio-1-only devices on pc-*-2.6:

  $ ./x86_64-softmmu/qemu-system-x86_64 -device virtio-vga -machine 
  qemu-system-x86_64: -device virtio-vga: Unable to set disable-legacy=off on a 
virtio-1.0 only device

Probably the simplest way to fix that is to append the following to

  { virtio-vga,        disable-modern, off },
  { virtio-gpu-pci,    disable-modern, off },
  { virtio-input-pci,  disable-modern, off },
  { virtio-crypto-pci, disable-modern, off }

We could also remove the property completely from those devices
(e.g. by moving virtio-vga to virtio_vga_info.non_transitional_name),
but it would break compatibility in case people are explicitly
setting "disable-modern=off" on those devices.


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