Re: [PATCH v6 01/10] qemu-options: New -compat to set policy for deprecated interfaces

[Eric Blake <eblake@redhat.com>]

On 3/12/21 9:32 AM, Markus Armbruster wrote:
> New option -compat lets you configure what to do when deprecated
> interfaces get used.  This is intended for testing users of the
> management interfaces.  It is experimental.
> 
> -compat deprecated-input=<input-policy> configures what to do when
> deprecated input is received.  Input policy can be "accept" (accept
> silently), or "reject" (reject the request with an error).
> 
> -compat deprecated-output=<out-policy> configures what to do when
> deprecated output is sent.  Output policy can be "accept" (pass on
> unchanged), or "hide" (filter out the deprecated parts).
> 
> Default is "accept".  Policies other than "accept" are implemented
> later in this series.
> 
> For now, -compat covers only syntactic aspects of QMP, i.e. stuff
> tagged with feature 'deprecated'.  We may want to extend it to cover
> semantic aspects, CLI, and experimental features.
> 
> Note that there is no good way for management application to detect
> presence of -compat: it's not visible output of query-qmp-schema or
> query-command-line-options.  Tolerable, because it's meant for
> testing.  If running with -compat fails, skip the test.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---

> +++ b/qapi/compat.json
> @@ -0,0 +1,51 @@
> +# -*- Mode: Python -*-
> +
> +##
> +# = Compatibility policy
> +##
> +
> +##
> +# @CompatPolicyInput:
> +#
> +# Policy for handling "funny" input.
> +#
> +# @accept: Accept silently
> +# @reject: Reject with an error
> +#
> +# Since: 5.2

6.0

> +##
> +{ 'enum': 'CompatPolicyInput',
> +  'data': [ 'accept', 'reject' ] }
> +
> +##
> +# @CompatPolicyOutput:
> +#
> +# Policy for handling "funny" output.
> +#
> +# @accept: Pass on unchanged
> +# @hide: Filter out
> +#
> +# Since: 5.2

and here

> +##
> +{ 'enum': 'CompatPolicyOutput',
> +  'data': [ 'accept', 'hide' ] }
> +
> +##
> +# @CompatPolicy:
> +#
> +# Policy for handling deprecated management interfaces.
> +#
> +# This is intended for testing users of the management interfaces.
> +#
> +# Limitation: covers only syntactic aspects of QMP, i.e. stuff tagged
> +# with feature 'deprecated'.  We may want to extend it to cover
> +# semantic aspects, CLI, and experimental features.
> +#
> +# @deprecated-input: how to handle deprecated input (default 'accept')
> +# @deprecated-output: how to handle deprecated output (default 'accept')
> +#
> +# Since: 5.2

and here

> +##
> +{ 'struct': 'CompatPolicy',
> +  'data': { '*deprecated-input': 'CompatPolicyInput',
> +            '*deprecated-output': 'CompatPolicyOutput' } }
> diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json
> index 3441c9a9ae..4912b9744e 100644

R-b still stands once you make the necessary tweaks.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org