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Mon, 20 Sep 2021 10:57:46 +0200 (CEST) From: Markus Armbruster To: Eric Blake Subject: Re: [PATCH RFC 1/5] qapi: Enable enum member introspection to show more than name References: <20210915192425.4104210-1-armbru@redhat.com> <20210915192425.4104210-2-armbru@redhat.com> <20210917135644.m37z2kpbel4lk6zn@redhat.com> Date: Mon, 20 Sep 2021 10:57:46 +0200 In-Reply-To: <20210917135644.m37z2kpbel4lk6zn@redhat.com> (Eric Blake's message of "Fri, 17 Sep 2021 08:56:44 -0500") Message-ID: <87bl4nd3p1.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.476, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, berrange@redhat.com, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com, Markus Armbruster , libvir-list@redhat.com, pkrempa@redhat.com, marcandre.lureau@redhat.com, jsnow@redhat.com, libguestfs@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > On Wed, Sep 15, 2021 at 09:24:21PM +0200, Markus Armbruster wrote: >> The next commit will add feature flags to enum members. There's a >> problem, though: query-qmp-schema shows an enum type's members as an >> array of member names (SchemaInfoEnum member @values). If it showed >> an array of objects with a name member, we could simply add more >> members to these objects. Since it's just strings, we can't. >> >> I can see three ways to correct this design mistake: >> >> 1. Do it the way we should have done it, plus compatibility goo. >> >> We want a ['SchemaInfoEnumMember'] member in SchemaInfoEnum. Since >> changing @values would be a compatibility break, add a new member >> @members instead. >> >> @values is now redundant. We should be able to get rid of it >> eventually. >> >> In my testing, output of qemu-system-x86_64's query-qmp-schema >> grows by 11% (18.5KiB). > > This makes sense if we plan to deprecate @values - if so, that > deprecation would make sense as part of this series, although we may > drag our feet for how long before we actually remove it. Yes. Changing query-qmp-schema requires extra care, as it is the very means for coping with change. >> >> 2. Like 1, but omit "boring" elements of @member, and empty @member. >> >> @values does not become redundant. Output of query-qmp-schema >> grows only as we make enum members non-boring. > > Does not change whether libvirt would have to learn to query the new > members, but adds a mandatory fallback step for learning about boring > members (although the fallback step will have to be there anyway for > older qemu). Peter probably has a better idea of which version is > nicer. > >> >> 3. Versioned query-qmp-schema. >> >> query-qmp-schema provides either @values or @members. The QMP >> client can select which version it wants. > > Sounds more complicated to implement. I'm not opposed to it, but am > leaning towards 1 or 2 myself. More on this in my reply to Peter. > >> >> This commit implements 1. simply because it's the solution I thought >> of first. I'm prepared to implement one of the others if we decide >> that's what we want. >> >> Signed-off-by: Markus Armbruster >> --- >> qapi/introspect.json | 20 ++++++++++++++++++-- >> scripts/qapi/introspect.py | 18 ++++++++++++++---- >> 2 files changed, 32 insertions(+), 6 deletions(-) >> >> diff --git a/qapi/introspect.json b/qapi/introspect.json >> index 39bd303778..250748cd95 100644 >> --- a/qapi/introspect.json >> +++ b/qapi/introspect.json >> @@ -142,14 +142,30 @@ >> # >> # Additional SchemaInfo members for meta-type 'enum'. >> # >> -# @values: the enumeration type's values, in no particular order. >> +# @members: the enum type's members, in no particular order. > > Missing a '(since 6.2)' tag. Yes. >> +# >> +# @values: the enumeration type's member names, in no particular order. >> +# Redundant with @members. Just for backward compatibility. > > Worth marking as deprecated in this patch, or in a followup? If we intend to deprecate, we can just as well do it right away. >> # >> # Values of this type are JSON string on the wire. >> # >> # Since: 2.5 >> ## >> { 'struct': 'SchemaInfoEnum', >> - 'data': { 'values': ['str'] } } >> + 'data': { 'members': [ 'SchemaInfoEnumMember' ], >> + 'values': ['str'] } } >> + >> +## >> +# @SchemaInfoEnumMember: >> +# >> +# An object member. >> +# >> +# @name: the member's name, as defined in the QAPI schema. >> +# >> +# Since: 6.1 > > 6.2 Whoops! >> +## >> +{ 'struct': 'SchemaInfoEnumMember', >> + 'data': { 'name': 'str' } } >> > > Definitely more flexible.