[PATCH 2/6] qemu: capabilities: Introduce QEMU_CAPS_COMPAT_DEPRECATED

[Martin Kletzander]

On Thu, Apr 01, 2021 at 10:07:15AM +0200, Peter Krempa wrote:
>On Thu, Apr 01, 2021 at 00:05:55 +0200, Martin Kletzander wrote:
>> On Fri, Mar 19, 2021 at 07:33:50PM +0100, Peter Krempa wrote:
>> > The capability is asserted if qemu supports the -compat
>> > deprecated-input= and deprecated-output= settings to control what should
>> > happen if deprecated fields are used in QMP.
>> >
>> > This will be used for a developer/tester-oriented setting which will
>> > aid us in catching use of deprecated settings sooner.
>> >
>> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
>> > ---
>> > src/qemu/qemu_capabilities.c                     | 8 ++++++++
>> > src/qemu/qemu_capabilities.h                     | 1 +
>> > tests/qemucapabilitiesdata/caps_6.0.0.x86_64.xml | 1 +
>> > 3 files changed, 10 insertions(+)
>> >
>> > diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>> > index dc1b10cd66..beea57caf6 100644
>> > --- a/src/qemu/qemu_capabilities.c
>> > +++ b/src/qemu/qemu_capabilities.c
>> > @@ -624,6 +624,7 @@ VIR_ENUM_IMPL(virQEMUCaps,
>> >               "audiodev",
>> >               "blockdev-backup",
>> >               "object.qapified",
>> > +              "compat-deprecated",
>> >     );
>> >
>> >
>> > @@ -5187,6 +5188,13 @@ virQEMUCapsInitProcessCapsInterlock(virQEMUCapsPtr qemuCaps)
>> >
>> >     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_BLOCKDEV))
>> >         virQEMUCapsSet(qemuCaps, QEMU_CAPS_BLOCKDEV_HOSTDEV_SCSI);
>> > +
>> > +    /* The -compat qemu command line argument is implemented using a newer
>> > +     * method which doesn't show up in query-command-line-options. As we'll use
>> > +     * it only for development and testing purposes we can base the capability
>> > +     * on a not entirely related witness. */
>> > +    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_QAPIFIED))
>> > +        virQEMUCapsSet(qemuCaps, QEMU_CAPS_COMPAT_DEPRECATED);
>>
>> Or it could be just enabled by default since it should be used by devs
>> and CI only.
>
>The idea here is that the capability will be used to hide the option
>from qemus which don't support it, so that you can e.g. downgrade your
>qemu or switch from git and non-git versions wihout having to touch this
>option.
>
>qemu-5.2.0:
>
>./qemu-system-x86_64 -compat
>qemu-system-x86_64: -compat: invalid option
>

Oh, good point, I haven't thought of the option itself.
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