Re: [PATCH v3 28/34] qapi: Implement deprecated-output=hide for QMP command results

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Hi
>
> On Sun, Mar 15, 2020 at 4:11 PM Markus Armbruster <address@hidden> wrote:
>>
>> This policy suppresses deprecated bits in output, and thus permits
>> "testing the future".  Implement it for QMP command results.  Example:
>> when QEMU is run with -compat deprecated-output=hide, then
>>
>>     {"execute": "query-cpus-fast"}
>>
>> yields
>>
>>     {"return": [{"thread-id": 9805, "props": {"core-id": 0, "thread-id": 0, 
>> "socket-id": 0}, "qom-path": "/machine/unattached/device[0]", "cpu-index": 
>> 0, "target": "x86_64"}]}
>>
>> instead of
>>
>>     {"return": [{"arch": "x86", "thread-id": 22436, "props": {"core-id": 0, 
>> "thread-id": 0, "socket-id": 0}, "qom-path": 
>> "/machine/unattached/device[0]", "cpu-index": 0, "target": "x86_64"}]}
>>
>> Note the suppression of deprecated member "arch".
>>
>> Signed-off-by: Markus Armbruster <address@hidden>
>> ---
>>  include/qapi/qobject-output-visitor.h   |  9 ++++++
>>  include/qapi/visitor-impl.h             |  3 ++
>>  include/qapi/visitor.h                  |  9 ++++++
>>  qapi/qapi-visit-core.c                  |  9 ++++++
>>  qapi/qobject-output-visitor.c           | 19 +++++++++++
>>  tests/test-qmp-cmds.c                   | 42 ++++++++++++++++++++++---
>>  qapi/trace-events                       |  1 +
>>  scripts/qapi/commands.py                |  2 +-
>>  scripts/qapi/visit.py                   | 12 +++++++
>>  tests/qapi-schema/qapi-schema-test.json | 17 +++++-----
>>  tests/qapi-schema/qapi-schema-test.out  | 18 +++++------
>>  11 files changed, 118 insertions(+), 23 deletions(-)
>>
>> diff --git a/include/qapi/qobject-output-visitor.h 
>> b/include/qapi/qobject-output-visitor.h
>> index 2b1726baf5..29f4ea6aad 100644
>> --- a/include/qapi/qobject-output-visitor.h
>> +++ b/include/qapi/qobject-output-visitor.h
>> @@ -53,4 +53,13 @@ typedef struct QObjectOutputVisitor QObjectOutputVisitor;
>>   */
>>  Visitor *qobject_output_visitor_new(QObject **result);
>>
>> +/*
>> + * Create a QObject output visitor for @obj for use with QMP
>> + *
>> + * This is like qobject_output_visitor_new(), except it obeys the
>> + * policy for handling deprecated management interfaces set with
>> + * -compat.
>> + */
>> +Visitor *qobject_output_visitor_new_qmp(QObject **result);
>> +
>>  #endif
>> diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
>> index 8ccb3b6c20..a6b26b7a5b 100644
>> --- a/include/qapi/visitor-impl.h
>> +++ b/include/qapi/visitor-impl.h
>> @@ -110,6 +110,9 @@ struct Visitor
>>         The core takes care of the return type in the public interface. */
>>      void (*optional)(Visitor *v, const char *name, bool *present);
>>
>> +    /* Optional */
>> +    bool (*deprecated)(Visitor *v, const char *name);
>> +
>>      /* Must be set */
>>      VisitorType type;
>>
>> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
>> index c5b23851a1..c89d51b2a4 100644
>> --- a/include/qapi/visitor.h
>> +++ b/include/qapi/visitor.h
>> @@ -449,6 +449,15 @@ void visit_end_alternate(Visitor *v, void **obj);
>>   */
>>  bool visit_optional(Visitor *v, const char *name, bool *present);
>>
>> +/*
>> + * Should we visit deprecated member @name?
>> + *
>> + * @name must not be NULL.  This function is only useful between
>> + * visit_start_struct() and visit_end_struct(), since only objects
>> + * have deprecated members.
>> + */
>> +bool visit_deprecated(Visitor *v, const char *name);
>> +
>>  /*
>>   * Visit an enum value.
>>   *
>> diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
>> index 5365561b07..501b3ccdef 100644
>> --- a/qapi/qapi-visit-core.c
>> +++ b/qapi/qapi-visit-core.c
>> @@ -137,6 +137,15 @@ bool visit_optional(Visitor *v, const char *name, bool 
>> *present)
>>      return *present;
>>  }
>>
>> +bool visit_deprecated(Visitor *v, const char *name)
>> +{
>> +    trace_visit_deprecated(v, name);
>> +    if (v->deprecated) {
>> +        return v->deprecated(v, name);
>> +    }
>> +    return true;
>> +}
>> +
>>  bool visit_is_input(Visitor *v)
>>  {
>>      return v->type == VISITOR_INPUT;
>> diff --git a/qapi/qobject-output-visitor.c b/qapi/qobject-output-visitor.c
>> index 26d7be5ec9..84cee17596 100644
>> --- a/qapi/qobject-output-visitor.c
>> +++ b/qapi/qobject-output-visitor.c
>> @@ -13,6 +13,7 @@
>>   */
>>
>>  #include "qemu/osdep.h"
>> +#include "qapi/compat-policy.h"
>>  #include "qapi/qobject-output-visitor.h"
>>  #include "qapi/visitor-impl.h"
>>  #include "qemu/queue.h"
>> @@ -31,6 +32,8 @@ typedef struct QStackEntry {
>>
>>  struct QObjectOutputVisitor {
>>      Visitor visitor;
>> +    CompatPolicyOutput deprecated_policy;
>> +
>>      QSLIST_HEAD(, QStackEntry) stack; /* Stack of unfinished containers */
>>      QObject *root; /* Root of the output visit */
>>      QObject **result; /* User's storage location for result */
>> @@ -198,6 +201,13 @@ static void qobject_output_type_null(Visitor *v, const 
>> char *name,
>>      qobject_output_add(qov, name, qnull());
>>  }
>>
>> +static bool qobject_output_deprecated(Visitor *v, const char *name)
>> +{
>> +    QObjectOutputVisitor *qov = to_qov(v);
>> +
>> +    return qov->deprecated_policy != COMPAT_POLICY_OUTPUT_HIDE;
>> +}
>> +
>>  /* Finish building, and return the root object.
>>   * The root object is never null. The caller becomes the object's
>>   * owner, and should use qobject_unref() when done with it.  */
>> @@ -247,6 +257,7 @@ Visitor *qobject_output_visitor_new(QObject **result)
>>      v->visitor.type_number = qobject_output_type_number;
>>      v->visitor.type_any = qobject_output_type_any;
>>      v->visitor.type_null = qobject_output_type_null;
>> +    v->visitor.deprecated = qobject_output_deprecated;
>>      v->visitor.complete = qobject_output_complete;
>>      v->visitor.free = qobject_output_free;
>>
>> @@ -255,3 +266,11 @@ Visitor *qobject_output_visitor_new(QObject **result)
>>
>>      return &v->visitor;
>>  }
>> +
>> +Visitor *qobject_output_visitor_new_qmp(QObject **result)
>> +{
>> +    QObjectOutputVisitor *v = to_qov(qobject_output_visitor_new(result));
>> +
>> +    v->deprecated_policy = compat_policy.deprecated_output;
>> +    return &v->visitor;
>> +}
>> diff --git a/tests/test-qmp-cmds.c b/tests/test-qmp-cmds.c
>> index d12ff47e26..82d599630c 100644
>> --- a/tests/test-qmp-cmds.c
>> +++ b/tests/test-qmp-cmds.c
>> @@ -1,4 +1,5 @@
>>  #include "qemu/osdep.h"
>> +#include "qapi/compat-policy.h"
>>  #include "qapi/qmp/qdict.h"
>>  #include "qapi/qmp/qjson.h"
>>  #include "qapi/qmp/qnum.h"
>> @@ -45,12 +46,17 @@ void qmp_user_def_cmd1(UserDefOne * ud1, Error **errp)
>>  {
>>  }
>>
>> -void qmp_test_features0(FeatureStruct0 *fs0, FeatureStruct1 *fs1,
>> -                       FeatureStruct2 *fs2, FeatureStruct3 *fs3,
>> -                       FeatureStruct4 *fs4, CondFeatureStruct1 *cfs1,
>> -                       CondFeatureStruct2 *cfs2, CondFeatureStruct3 *cfs3,
>> -                       Error **errp)
>> +FeatureStruct1 *qmp_test_features0(bool has_fs0, FeatureStruct0 *fs0,
>> +                                   bool has_fs1, FeatureStruct1 *fs1,
>> +                                   bool has_fs2, FeatureStruct2 *fs2,
>> +                                   bool has_fs3, FeatureStruct3 *fs3,
>> +                                   bool has_fs4, FeatureStruct4 *fs4,
>> +                                   bool has_cfs1, CondFeatureStruct1 *cfs1,
>> +                                   bool has_cfs2, CondFeatureStruct2 *cfs2,
>> +                                   bool has_cfs3, CondFeatureStruct3 *cfs3,
>> +                                   Error **errp)
>>  {
>> +    return g_new(FeatureStruct1, 1);
>>  }
>>
>>  void qmp_test_command_features1(Error **errp)
>> @@ -271,6 +277,30 @@ static void test_dispatch_cmd_io(void)
>>      qobject_unref(ret3);
>>  }
>>
>> +static void test_dispatch_cmd_ret_deprecated(void)
>> +{
>> +    const char *cmd = "{ 'execute': 'test-features0' }";
>> +    QDict *ret;
>> +
>> +    memset(&compat_policy, 0, sizeof(compat_policy));
>> +
>> +    /* default accept */
>> +    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
>> +    assert(ret && qdict_size(ret) == 1);
>> +    qobject_unref(ret);
>> +
>> +    compat_policy.has_deprecated_output = true;
>> +    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_ACCEPT;
>> +    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
>> +    assert(ret && qdict_size(ret) == 1);
>> +    qobject_unref(ret);
>> +
>> +    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
>> +    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
>> +    assert(ret && qdict_size(ret) == 0);
>> +    qobject_unref(ret);
>> +}
>> +
>>  /* test generated dealloc functions for generated types */
>>  static void test_dealloc_types(void)
>>  {
>> @@ -345,6 +375,8 @@ int main(int argc, char **argv)
>>      g_test_add_func("/qmp/dispatch_cmd_io", test_dispatch_cmd_io);
>>      g_test_add_func("/qmp/dispatch_cmd_success_response",
>>                      test_dispatch_cmd_success_response);
>> +    g_test_add_func("/qmp/dispatch_cmd_ret_deprecated",
>> +                    test_dispatch_cmd_ret_deprecated);
>>      g_test_add_func("/qmp/dealloc_types", test_dealloc_types);
>>      g_test_add_func("/qmp/dealloc_partial", test_dealloc_partial);
>>
>> diff --git a/qapi/trace-events b/qapi/trace-events
>> index 5eb4afa110..eff1fbd199 100644
>> --- a/qapi/trace-events
>> +++ b/qapi/trace-events
>> @@ -17,6 +17,7 @@ visit_start_alternate(void *v, const char *name, void 
>> *obj, size_t size) "v=%p n
>>  visit_end_alternate(void *v, void *obj) "v=%p obj=%p"
>>
>>  visit_optional(void *v, const char *name, bool *present) "v=%p name=%s 
>> present=%p"
>> +visit_deprecated(void *v, const char *name) "v=%p name=%s"
>>
>>  visit_type_enum(void *v, const char *name, int *obj) "v=%p name=%s obj=%p"
>>  visit_type_int(void *v, const char *name, int64_t *obj) "v=%p name=%s 
>> obj=%p"
>> diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
>> index bc30876c88..35b79c554d 100644
>> --- a/scripts/qapi/commands.py
>> +++ b/scripts/qapi/commands.py
>> @@ -69,7 +69,7 @@ static void qmp_marshal_output_%(c_name)s(%(c_type)s 
>> ret_in, QObject **ret_out,
>>      Error *err = NULL;
>>      Visitor *v;
>>
>> -    v = qobject_output_visitor_new(ret_out);
>> +    v = qobject_output_visitor_new_qmp(ret_out);
>>      visit_type_%(c_name)s(v, "unused", &ret_in, &err);
>>      if (!err) {
>>          visit_complete(v, ret_out);
>> diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
>> index 23d9194aa4..21df3abed2 100644
>> --- a/scripts/qapi/visit.py
>> +++ b/scripts/qapi/visit.py
>> @@ -56,6 +56,7 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s 
>> *obj, Error **errp)
>>                       c_type=base.c_name())
>>
>>      for memb in members:
>> +        deprecated = 'deprecated' in [f.name for f in memb.features]
>>          ret += gen_if(memb.ifcond)
>>          if memb.optional:
>>              ret += mcgen('''
>> @@ -63,6 +64,12 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s 
>> *obj, Error **errp)
>>  ''',
>>                           name=memb.name, c_name=c_name(memb.name))
>>              push_indent()
>> +        if deprecated:
>> +            ret += mcgen('''
>> +    if (visit_deprecated(v, "%(name)s")) {
>
> Do you have a compelling case where the "name" would change the
> deprecation policy? I think that could be more confusing than
> necessary, say if x- name wouldn't follow the policy.

Yes, that would be a bad idea.

Intended use is error messages, just like we do elsewhere.  The output
visitor's method qobject_output_deprecated() can't fail, but the input
visitor's method can; see PATCH 33.

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