Re: [PATCH 1/9] qapi: New special feature flag "unstable"

[Kashyap Chamarthy <kchamart@redhat.com>]

On Tue, Oct 26, 2021 at 09:15:30AM +0200, Markus Armbruster wrote:
> Kashyap Chamarthy <kchamart@redhat.com> writes:
> 
> > On Mon, Oct 25, 2021 at 07:25:24AM +0200, Markus Armbruster wrote:

[...]

> > Looks like there's another stable property with an "x-" prefix:
> > "x-remote-object", part of QOM type @RemoteObjectProperties.
> 
> The union branch 'x-remote-object' isn't flagged 'unstable' (because
> union branches can't have feature flags), but the enumeration value
> 'x-remote-object' is.  Sufficient, because you can't use the branch
> without using the enumeration value.  Admittedly subtle.

Ah, thanks for the explanation.  I missed the union branch part, which
I now notice in your "[PATCH 2/9] qapi: Mark unstable QMP parts
with feature 'unstable'".

> I wrote a bit of code (appended) to make sure I don't miss names.

Thanks; looks good to me.

> > Given the above "x-" properties are now stable, I take it that they
> > cannot be renamed now, as they might break any tools using them?  My
> > guess is the tedious way is not worth it: deprecate them, and add the
> > non-x variants as "synonyms".  
> 
> "x-use-canonical-path-for-ramblock-id" goes back to commit fa0cb34d22
> "hostmem: use object id for memory region name with >= 4.0" (v4.0).  It
> may have been intended to be internal back then.  It wasn't anymore when
> commit 8db0b20415 "machine: add missing doc for memory-backend option"
> (v6.0) documented it:
> 
>     And document that x-use-canonical-path-for-ramblock-id,
>     is considered to be stable to make sure it won't go away by accident.
>     
>     x- was intended for unstable/iternal properties, and not supposed to
>     be stable option. However it's too late to rename (drop x-)
>     it as it would mean that users will have to mantain both
>     x-use-canonical-path-for-ramblock-id (for QEMU 5.0-5.2) versions
>     and prefix-less for later versions.
> 
> Igor's reasoning still applies.
> 
> "x-origin" has always been stable.  Same argument.

Yep, fair enough.

[...]
 
> commit 415b71a9f6e5bc37e84895d2e767cf4cfacd279b (HEAD)
> Author: Markus Armbruster <armbru@redhat.com>
> Date:   Sat Oct 9 09:01:21 2021 +0200
> 
>     qapi: Find x- without feature unstable DBG
> 
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index b7b3fc0ce4..f2af1d7eea 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -14,6 +14,8 @@
>  
>  # TODO catching name collisions in generated code would be nice
>  
> +import sys
> +
>  from collections import OrderedDict
>  import os
>  import re
> @@ -118,6 +120,11 @@ def describe(self):
>          return "%s '%s'" % (self.meta, self.name)
>  
>  
> +def check_have_feature_unstable(name, info, features):
> +    if name.startswith('x-') and 'unstable' not in (f.name for f in features):
> +        print(QAPISemError(info, f"XXX %{name} %{features}"), file=sys.stderr)
> +
> +
>  class QAPISchemaVisitor:
>      def visit_begin(self, schema):
>          pass
> @@ -718,6 +725,7 @@ def __init__(self, name, info, ifcond=None, features=None):
>          self.features = features or []
>  
>      def connect_doc(self, doc):
> +        check_have_feature_unstable(self.name, self.info, self.features)
>          super().connect_doc(doc)
>          if doc:
>              for f in self.features:
> @@ -745,6 +753,7 @@ def __init__(self, name, info, typ, optional, ifcond=None, features=None):
>          self.features = features or []
>  
>      def check(self, schema):
> +        check_have_feature_unstable(self.name, self.info, self.features)
>          assert self.defined_in
>          self.type = schema.resolve_type(self._type_name, self.info,
>                                          self.describe)
> @@ -789,6 +798,7 @@ def __init__(self, name, info, doc, ifcond, features,
>  
>      def check(self, schema):
>          super().check(schema)
> +        check_have_feature_unstable(self.name, self.info, self.features)
>          if self._arg_type_name:
>              self.arg_type = schema.resolve_type(
>                  self._arg_type_name, self.info, "command's 'data'")
> @@ -844,6 +854,7 @@ def __init__(self, name, info, doc, ifcond, features, arg_type, boxed):
>  
>      def check(self, schema):
>          super().check(schema)
> +        check_have_feature_unstable(self.name, self.info, self.features)
>          if self._arg_type_name:
>              self.arg_type = schema.resolve_type(
>                  self._arg_type_name, self.info, "event's 'data'")

TIL: the error class QAPISemError() 

Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>    

-- 
/kashyap