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.
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.
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 <armbru@redhat.com> --- 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.
+# +# @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?
# # 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
+## +{ 'struct': 'SchemaInfoEnumMember', + 'data': { 'name': 'str' } }
Definitely more flexible. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org