Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2021-03-16-v4' into staging

QAPI patches patches for 2021-03-16

# gpg: Signature made Fri 19 Mar 2021 15:06:52 GMT
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2021-03-16-v4:
  qapi: New -compat deprecated-input=crash
  qapi: Implement deprecated-input=reject for QMP command arguments
  qapi: Implement deprecated-input=reject for QMP commands
  test-util-sockets: Add stub for monitor_set_cur()
  qapi: Implement deprecated-output=hide for QMP introspection
  monitor: Drop query-qmp-schema 'gen': false hack
  qapi: Implement deprecated-output=hide for QMP event data
  qapi: Implement deprecated-output=hide for QMP events
  qapi: Implement deprecated-output=hide for QMP command results
  qemu-options: New -compat to set policy for deprecated interfaces
  qemuutil: remove qemu_set_fd_handler duplicate symbol

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

31 files changed, 549 insertions, 64 deletions

diff --git a/include/qapi/compat-policy.h b/include/qapi/compat-policy.h
new file mode 100644
index 0000000000..1083f95122
--- /dev/null
+++ b/include/qapi/compat-policy.h
@@ -0,0 +1,38 @@
+/*
+ * Policy for handling "funny" management interfaces
+ *
+ * Copyright (C) 2020 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#ifndef QAPI_COMPAT_POLICY_H
+#define QAPI_COMPAT_POLICY_H
+
+#include "qapi/qapi-types-compat.h"
+
+extern CompatPolicy compat_policy;
+
+/*
+ * Create a QObject input visitor for @obj for use with QMP
+ *
+ * This is like qobject_input_visitor_new(), except it obeys the
+ * policy for handling deprecated management interfaces set with
+ * -compat.
+ */
+Visitor *qobject_input_visitor_new_qmp(QObject *obj);
+
+/*
+ * 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/qmp/dispatch.h b/include/qapi/qmp/dispatch.h
index 135dfdef71..075203dc67 100644
--- a/include/qapi/qmp/dispatch.h
+++ b/include/qapi/qmp/dispatch.h
@@ -26,6 +26,7 @@ typedef enum QmpCommandOptions
     QCO_ALLOW_OOB             =  (1U << 1),
     QCO_ALLOW_PRECONFIG       =  (1U << 2),
     QCO_COROUTINE             =  (1U << 3),
+    QCO_DEPRECATED            =  (1U << 4),
 } QmpCommandOptions;
 
 typedef struct QmpCommand
diff --git a/include/qapi/qobject-input-visitor.h b/include/qapi/qobject-input-visitor.h
index 95985e25e5..8d69388810 100644
--- a/include/qapi/qobject-input-visitor.h
+++ b/include/qapi/qobject-input-visitor.h
@@ -15,6 +15,7 @@
 #ifndef QOBJECT_INPUT_VISITOR_H
 #define QOBJECT_INPUT_VISITOR_H
 
+#include "qapi/qapi-types-compat.h"
 #include "qapi/visitor.h"
 
 typedef struct QObjectInputVisitor QObjectInputVisitor;
@@ -58,6 +59,9 @@ typedef struct QObjectInputVisitor QObjectInputVisitor;
  */
 Visitor *qobject_input_visitor_new(QObject *obj);
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                      CompatPolicyInput deprecated);
+
 /*
  * Create a QObject input visitor for @obj for use with keyval_parse()
  *
diff --git a/include/qapi/qobject-output-visitor.h b/include/qapi/qobject-output-visitor.h
index 2b1726baf5..f2a2f92a00 100644
--- a/include/qapi/qobject-output-visitor.h
+++ b/include/qapi/qobject-output-visitor.h
@@ -15,6 +15,7 @@
 #define QOBJECT_OUTPUT_VISITOR_H
 
 #include "qapi/visitor.h"
+#include "qapi/qapi-types-compat.h"
 
 typedef struct QObjectOutputVisitor QObjectOutputVisitor;
 
@@ -53,4 +54,7 @@ typedef struct QObjectOutputVisitor QObjectOutputVisitor;
  */
 Visitor *qobject_output_visitor_new(QObject **result);
 
+void qobject_output_visitor_set_policy(Visitor *v,
+                                       CompatPolicyOutput deprecated);
+
 #endif
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 7362c043be..3b950f6e3d 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -113,6 +113,12 @@ 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_accept)(Visitor *v, const char *name, Error **errp);
+
+    /* 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 ebc19ede7f..b3c9ef7a81 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -460,6 +460,24 @@ void visit_end_alternate(Visitor *v, void **obj);
 bool visit_optional(Visitor *v, const char *name, bool *present);
 
 /*
+ * Should we reject 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_accept(Visitor *v, const char *name, Error **errp);
+
+/*
+ * 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.
  *
  * @name expresses the relationship of this enum to its parent
diff --git a/monitor/misc.c b/monitor/misc.c
index b103bd0a92..55f3744053 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -231,8 +231,6 @@ static void monitor_init_qmp_commands(void)
 
     qmp_init_marshal(&qmp_commands);
 
-    qmp_register_command(&qmp_commands, "query-qmp-schema",
-                         qmp_query_qmp_schema, QCO_ALLOW_PRECONFIG);
     qmp_register_command(&qmp_commands, "device_add", qmp_device_add,
                          QCO_NO_OPTIONS);
 
diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 40903d6386..9c3a09cb01 100644
--- a/monitor/monitor-internal.h
+++ b/monitor/monitor-internal.h
@@ -183,7 +183,4 @@ void help_cmd(Monitor *mon, const char *name);
 void handle_hmp_command(MonitorHMP *mon, const char *cmdline);
 int hmp_compare_cmd(const char *name, const char *list);
 
-void qmp_query_qmp_schema(QDict *qdict, QObject **ret_data,
-                                 Error **errp);
-
 #endif
diff --git a/monitor/qmp-cmds-control.c b/monitor/qmp-cmds-control.c
index 513b547233..6e581713a3 100644
--- a/monitor/qmp-cmds-control.c
+++ b/monitor/qmp-cmds-control.c
@@ -26,10 +26,14 @@
 
 #include "monitor-internal.h"
 #include "qemu-version.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-control.h"
+#include "qapi/qapi-commands-introspect.h"
 #include "qapi/qapi-emit-events.h"
 #include "qapi/qapi-introspect.h"
+#include "qapi/qapi-visit-introspect.h"
+#include "qapi/qobject-input-visitor.h"
 
 /*
  * Accept QMP capabilities in @list for @mon.
@@ -130,17 +134,89 @@ CommandInfoList *qmp_query_commands(Error **errp)
     return list;
 }
 
-/*
- * Minor hack: generated marshalling suppressed for this command
- * ('gen': false in the schema) so we can parse the JSON string
- * directly into QObject instead of first parsing it with
- * visit_type_SchemaInfoList() into a SchemaInfoList, then marshal it
- * to QObject with generated output marshallers, every time.  Instead,
- * we do it in test-qobject-input-visitor.c, just to make sure
- * qapi-gen.py's output actually conforms to the schema.
- */
-void qmp_query_qmp_schema(QDict *qdict, QObject **ret_data,
-                                 Error **errp)
+static void *split_off_generic_list(void *list,
+                                    bool (*splitp)(void *elt),
+                                    void **part)
+{
+    GenericList *keep = NULL, **keep_tailp = &keep;
+    GenericList *split = NULL, **split_tailp = &split;
+    GenericList *tail;
+
+    for (tail = list; tail; tail = tail->next) {
+        if (splitp(tail)) {
+            *split_tailp = tail;
+            split_tailp = &tail->next;
+        } else {
+            *keep_tailp = tail;
+            keep_tailp = &tail->next;
+        }
+    }
+
+    *keep_tailp = *split_tailp = NULL;
+    *part = split;
+    return keep;
+}
+
+static bool is_in(const char *s, strList *list)
+{
+    strList *tail;
+
+    for (tail = list; tail; tail = tail->next) {
+        if (!strcmp(tail->value, s)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static bool is_entity_deprecated(void *link)
+{
+    return is_in("deprecated", ((SchemaInfoList *)link)->value->features);
+}
+
+static bool is_member_deprecated(void *link)
+{
+    return is_in("deprecated",
+                 ((SchemaInfoObjectMemberList *)link)->value->features);
+}
+
+static SchemaInfoList *zap_deprecated(SchemaInfoList *schema)
 {
-    *ret_data = qobject_from_qlit(&qmp_schema_qlit);
+    void *to_zap;
+    SchemaInfoList *tail;
+    SchemaInfo *ent;
+
+    schema = split_off_generic_list(schema, is_entity_deprecated, &to_zap);
+    qapi_free_SchemaInfoList(to_zap);
+
+    for (tail = schema; tail; tail = tail->next) {
+        ent = tail->value;
+        if (ent->meta_type == SCHEMA_META_TYPE_OBJECT) {
+            ent->u.object.members
+                = split_off_generic_list(ent->u.object.members,
+                                         is_member_deprecated, &to_zap);
+            qapi_free_SchemaInfoObjectMemberList(to_zap);
+        }
+    }
+
+    return schema;
+}
+
+SchemaInfoList *qmp_query_qmp_schema(Error **errp)
+{
+    QObject *obj = qobject_from_qlit(&qmp_schema_qlit);
+    Visitor *v = qobject_input_visitor_new(obj);
+    SchemaInfoList *schema = NULL;
+
+    /* test_visitor_in_qmp_introspect() ensures this can't fail */
+    visit_type_SchemaInfoList(v, NULL, &schema, &error_abort);
+    g_assert(schema);
+
+    qobject_unref(obj);
+    visit_free(v);
+
+    if (compat_policy.deprecated_output == COMPAT_POLICY_OUTPUT_HIDE) {
+        return zap_deprecated(schema);
+    }
+    return schema;
 }
diff --git a/qapi/compat.json b/qapi/compat.json
new file mode 100644
index 0000000000..ae3afc22df
--- /dev/null
+++ b/qapi/compat.json
@@ -0,0 +1,52 @@
+# -*- Mode: Python -*-
+
+##
+# = Compatibility policy
+##
+
+##
+# @CompatPolicyInput:
+#
+# Policy for handling "funny" input.
+#
+# @accept: Accept silently
+# @reject: Reject with an error
+# @crash: abort() the process
+#
+# Since: 6.0
+##
+{ 'enum': 'CompatPolicyInput',
+  'data': [ 'accept', 'reject', 'crash' ] }
+
+##
+# @CompatPolicyOutput:
+#
+# Policy for handling "funny" output.
+#
+# @accept: Pass on unchanged
+# @hide: Filter out
+#
+# Since: 6.0
+##
+{ '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: 6.0
+##
+{ 'struct': 'CompatPolicy',
+  'data': { '*deprecated-input': 'CompatPolicyInput',
+            '*deprecated-output': 'CompatPolicyOutput' } }
diff --git a/qapi/introspect.json b/qapi/introspect.json
index 944bb87a20..39bd303778 100644
--- a/qapi/introspect.json
+++ b/qapi/introspect.json
@@ -49,7 +49,7 @@
 ##
 { 'command': 'query-qmp-schema',
   'returns': [ 'SchemaInfo' ],
-  'gen': false }                # just to simplify qmp_query_json()
+  'allow-preconfig': true }
 
 ##
 # @SchemaMetaType:
diff --git a/qapi/meson.build b/qapi/meson.build
index d4424ae6e7..0d20226fa3 100644
--- a/qapi/meson.build
+++ b/qapi/meson.build
@@ -25,6 +25,7 @@ qapi_all_modules = [
   'block-export',
   'char',
   'common',
+  'compat',
   'control',
   'crypto',
   'dump',
diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json
index 3441c9a9ae..4912b9744e 100644
--- a/qapi/qapi-schema.json
+++ b/qapi/qapi-schema.json
@@ -79,6 +79,7 @@
 { 'include': 'migration.json' }
 { 'include': 'transaction.json' }
 { 'include': 'trace.json' }
+{ 'include': 'compat.json' }
 { 'include': 'control.json' }
 { 'include': 'introspect.json' }
 { 'include': 'qom.json' }
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 7e5f40e7f0..a641adec51 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -135,6 +135,24 @@ bool visit_optional(Visitor *v, const char *name, bool *present)
     return *present;
 }
 
+bool visit_deprecated_accept(Visitor *v, const char *name, Error **errp)
+{
+    trace_visit_deprecated_accept(v, name);
+    if (v->deprecated_accept) {
+        return v->deprecated_accept(v, name, errp);
+    }
+    return true;
+}
+
+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/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 5e597c76f7..59600210ce 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -14,15 +14,36 @@
 #include "qemu/osdep.h"
 
 #include "block/aio.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/dispatch.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
+#include "qapi/qobject-input-visitor.h"
+#include "qapi/qobject-output-visitor.h"
 #include "sysemu/runstate.h"
 #include "qapi/qmp/qbool.h"
 #include "qemu/coroutine.h"
 #include "qemu/main-loop.h"
 
+CompatPolicy compat_policy;
+
+Visitor *qobject_input_visitor_new_qmp(QObject *obj)
+{
+    Visitor *v = qobject_input_visitor_new(obj);
+
+    qobject_input_visitor_set_policy(v, compat_policy.deprecated_input);
+    return v;
+}
+
+Visitor *qobject_output_visitor_new_qmp(QObject **result)
+{
+    Visitor *v = qobject_output_visitor_new(result);
+
+    qobject_output_visitor_set_policy(v, compat_policy.deprecated_output);
+    return v;
+}
+
 static QDict *qmp_dispatch_check_obj(QDict *dict, bool allow_oob,
                                      Error **errp)
 {
@@ -155,6 +176,20 @@ QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request,
                   "The command %s has not been found", command);
         goto out;
     }
+    if (cmd->options & QCO_DEPRECATED) {
+        switch (compat_policy.deprecated_input) {
+        case COMPAT_POLICY_INPUT_ACCEPT:
+            break;
+        case COMPAT_POLICY_INPUT_REJECT:
+            error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
+                      "Deprecated command %s disabled by policy",
+                      command);
+            goto out;
+        case COMPAT_POLICY_INPUT_CRASH:
+        default:
+            abort();
+        }
+    }
     if (!cmd->enabled) {
         error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
                   "Command %s has been disabled%s%s",
diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index 23843b242e..04b790412e 100644
--- a/qapi/qobject-input-visitor.c
+++ b/qapi/qobject-input-visitor.c
@@ -14,6 +14,7 @@
 
 #include "qemu/osdep.h"
 #include <math.h>
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/visitor-impl.h"
@@ -43,6 +44,7 @@ typedef struct StackObject {
 
 struct QObjectInputVisitor {
     Visitor visitor;
+    CompatPolicyInput deprecated_policy;
 
     /* Root of visit at visitor creation. */
     QObject *root;
@@ -662,6 +664,24 @@ static void qobject_input_optional(Visitor *v, const char *name, bool *present)
     *present = true;
 }
 
+static bool qobject_input_deprecated_accept(Visitor *v, const char *name,
+                                            Error **errp)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    switch (qiv->deprecated_policy) {
+    case COMPAT_POLICY_INPUT_ACCEPT:
+        return true;
+    case COMPAT_POLICY_INPUT_REJECT:
+        error_setg(errp, "Deprecated parameter '%s' disabled by policy",
+                   name);
+        return false;
+    case COMPAT_POLICY_INPUT_CRASH:
+    default:
+        abort();
+    }
+}
+
 static void qobject_input_free(Visitor *v)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
@@ -696,6 +716,7 @@ static QObjectInputVisitor *qobject_input_visitor_base_new(QObject *obj)
     v->visitor.end_list = qobject_input_end_list;
     v->visitor.start_alternate = qobject_input_start_alternate;
     v->visitor.optional = qobject_input_optional;
+    v->visitor.deprecated_accept = qobject_input_deprecated_accept;
     v->visitor.free = qobject_input_free;
 
     v->root = qobject_ref(obj);
@@ -718,6 +739,14 @@ Visitor *qobject_input_visitor_new(QObject *obj)
     return &v->visitor;
 }
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                       CompatPolicyInput deprecated)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    qiv->deprecated_policy = deprecated;
+}
+
 Visitor *qobject_input_visitor_new_keyval(QObject *obj)
 {
     QObjectInputVisitor *v = qobject_input_visitor_base_new(obj);
diff --git a/qapi/qobject-output-visitor.c b/qapi/qobject-output-visitor.c
index ba6f6ac8a7..e4873308d4 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 */
@@ -207,6 +210,13 @@ static bool qobject_output_type_null(Visitor *v, const char *name,
     return true;
 }
 
+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.  */
@@ -256,6 +266,7 @@ 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;
 
@@ -264,3 +275,11 @@ Visitor *qobject_output_visitor_new(QObject **result)
 
     return &v->visitor;
 }
+
+void qobject_output_visitor_set_policy(Visitor *v,
+                                       CompatPolicyOutput deprecated)
+{
+    QObjectOutputVisitor *qov = to_qov(v);
+
+    qov->deprecated_policy = deprecated;
+}
diff --git a/qapi/trace-events b/qapi/trace-events
index 5eb4afa110..3cabe912ae 100644
--- a/qapi/trace-events
+++ b/qapi/trace-events
@@ -17,6 +17,8 @@ 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_accept(void *v, const char *name) "v=%p name=%s"
+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/qemu-options.hx b/qemu-options.hx
index 671b310ab8..d60a03d3a9 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3507,6 +3507,28 @@ DEFHEADING()
 
 DEFHEADING(Debug/Expert options:)
 
+DEF("compat", HAS_ARG, QEMU_OPTION_compat,
+    "-compat [deprecated-input=accept|reject|crash][,deprecated-output=accept|hide]\n"
+    "                Policy for handling deprecated management interfaces\n",
+    QEMU_ARCH_ALL)
+SRST
+``-compat [deprecated-input=@var{input-policy}][,deprecated-output=@var{output-policy}]``
+    Set policy for handling deprecated management interfaces (experimental):
+
+    ``deprecated-input=accept`` (default)
+        Accept deprecated commands and arguments
+    ``deprecated-input=reject``
+        Reject deprecated commands and arguments
+    ``deprecated-input=crash``
+        Crash on deprecated commands and arguments
+    ``deprecated-output=accept`` (default)
+        Emit deprecated command results and events
+    ``deprecated-output=hide``
+        Suppress deprecated command results and events
+
+    Limitation: covers only syntactic aspects of QMP.
+ERST
+
 DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
     "-fw_cfg [name=]<name>,file=<file>\n"
     "                add named fw_cfg entry with contents from file\n"
diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index 0a75a9371b..0e13d51054 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -96,7 +96,7 @@ static void qmp_marshal_output_%(c_name)s(%(c_type)s ret_in,
 {
     Visitor *v;
 
-    v = qobject_output_visitor_new(ret_out);
+    v = qobject_output_visitor_new_qmp(ret_out);
     if (visit_type_%(c_name)s(v, "unused", &ret_in, errp)) {
         visit_complete(v, ret_out);
     }
@@ -154,7 +154,7 @@ def gen_marshal(name: str,
 
     ret += mcgen('''
 
-    v = qobject_input_visitor_new(QOBJECT(args));
+    v = qobject_input_visitor_new_qmp(QOBJECT(args));
     if (!visit_start_struct(v, NULL, NULL, 0, errp)) {
         goto out;
     }
@@ -210,12 +210,16 @@ out:
 
 
 def gen_register_command(name: str,
+                         features: List[QAPISchemaFeature],
                          success_response: bool,
                          allow_oob: bool,
                          allow_preconfig: bool,
                          coroutine: bool) -> str:
     options = []
 
+    if 'deprecated' in [f.name for f in features]:
+        options += ['QCO_DEPRECATED']
+
     if not success_response:
         options += ['QCO_NO_SUCCESS_RESP']
     if allow_oob:
@@ -251,10 +255,9 @@ class QAPISchemaGenCommandVisitor(QAPISchemaModularCVisitor):
         visit = self._module_basename('qapi-visit', name)
         self._genc.add(mcgen('''
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/visitor.h"
 #include "qapi/qmp/qdict.h"
-#include "qapi/qobject-output-visitor.h"
-#include "qapi/qobject-input-visitor.h"
 #include "qapi/dealloc-visitor.h"
 #include "qapi/error.h"
 #include "%(visit)s.h"
@@ -326,9 +329,9 @@ void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds)
             self._genc.add(gen_marshal(name, arg_type, boxed, ret_type))
         with self._temp_module('./init'):
             with ifcontext(ifcond, self._genh, self._genc):
-                self._genc.add(gen_register_command(name, success_response,
-                                                    allow_oob, allow_preconfig,
-                                                    coroutine))
+                self._genc.add(gen_register_command(
+                    name, features, success_response, allow_oob,
+                    allow_preconfig, coroutine))
 
 
 def gen_commands(schema: QAPISchema,
diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
index 90d2f6156d..fee8c671e7 100644
--- a/scripts/qapi/events.py
+++ b/scripts/qapi/events.py
@@ -79,6 +79,7 @@ def gen_param_var(typ: QAPISchemaObjectType) -> str:
 
 def gen_event_send(name: str,
                    arg_type: Optional[QAPISchemaObjectType],
+                   features: List[QAPISchemaFeature],
                    boxed: bool,
                    event_enum_name: str,
                    event_emit: str) -> str:
@@ -107,6 +108,14 @@ def gen_event_send(name: str,
         if not boxed:
             ret += gen_param_var(arg_type)
 
+    if 'deprecated' in [f.name for f in features]:
+        ret += mcgen('''
+
+    if (compat_policy.deprecated_output == COMPAT_POLICY_OUTPUT_HIDE) {
+        return;
+    }
+''')
+
     ret += mcgen('''
 
     qmp = qmp_event_build_dict("%(name)s");
@@ -117,7 +126,7 @@ def gen_event_send(name: str,
     if have_args:
         assert arg_type is not None
         ret += mcgen('''
-    v = qobject_output_visitor_new(&obj);
+    v = qobject_output_visitor_new_qmp(&obj);
 ''')
         if not arg_type.is_implicit():
             ret += mcgen('''
@@ -136,7 +145,11 @@ def gen_event_send(name: str,
         ret += mcgen('''
 
     visit_complete(v, &obj);
-    qdict_put_obj(qmp, "data", obj);
+    if (qdict_size(qobject_to(QDict, obj))) {
+        qdict_put_obj(qmp, "data", obj);
+    } else {
+        qobject_unref(obj);
+    }
 ''')
 
     ret += mcgen('''
@@ -176,9 +189,9 @@ class QAPISchemaGenEventVisitor(QAPISchemaModularCVisitor):
 #include "%(prefix)sqapi-emit-events.h"
 #include "%(events)s.h"
 #include "%(visit)s.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
-#include "qapi/qobject-output-visitor.h"
 #include "qapi/qmp-event.h"
 
 ''',
@@ -220,7 +233,7 @@ void %(event_emit)s(%(event_enum)s event, QDict *qdict);
                     boxed: bool) -> None:
         with ifcontext(ifcond, self._genh, self._genc):
             self._genh.add(gen_event_send_decl(name, arg_type, boxed))
-            self._genc.add(gen_event_send(name, arg_type, boxed,
+            self._genc.add(gen_event_send(name, arg_type, features, boxed,
                                           self._event_enum_name,
                                           self._event_emit_name))
         # Note: we generate the enum member regardless of @ifcond, to
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 9aa0b1e11e..9e96f3c566 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -77,6 +77,7 @@ bool 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('''
@@ -84,6 +85,15 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
 ''',
                          name=memb.name, c_name=c_name(memb.name))
             indent.increase()
+        if deprecated:
+            ret += mcgen('''
+    if (!visit_deprecated_accept(v, "%(name)s", errp)) {
+        return false;
+    }
+    if (visit_deprecated(v, "%(name)s")) {
+''',
+                         name=memb.name)
+            indent.increase()
         ret += mcgen('''
     if (!visit_type_%(c_type)s(v, "%(name)s", &obj->%(c_name)s, errp)) {
         return false;
@@ -91,6 +101,11 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
 ''',
                      c_type=memb.type.c_name(), name=memb.name,
                      c_name=c_name(memb.name))
+        if deprecated:
+            indent.decrease()
+            ret += mcgen('''
+    }
+''')
         if memb.optional:
             indent.decrease()
             ret += mcgen('''
diff --git a/softmmu/vl.c b/softmmu/vl.c
index d7f0b029dc..aadb526138 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -29,6 +29,7 @@
 #include "exec/cpu-common.h"
 #include "hw/boards.h"
 #include "hw/qdev-properties.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
@@ -114,6 +115,7 @@
 #include "sysemu/replay.h"
 #include "qapi/qapi-events-run-state.h"
 #include "qapi/qapi-visit-block-core.h"
+#include "qapi/qapi-visit-compat.h"
 #include "qapi/qapi-visit-ui.h"
 #include "qapi/qapi-commands-block-core.h"
 #include "qapi/qapi-commands-migration.h"
@@ -3452,6 +3454,21 @@ void qemu_init(int argc, char **argv, char **envp)
                 enable_mlock = qemu_opt_get_bool(opts, "mem-lock", false);
                 enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", false);
                 break;
+            case QEMU_OPTION_compat:
+                {
+                    CompatPolicy *opts;
+                    Visitor *v;
+
+                    v = qobject_input_visitor_new_str(optarg, NULL,
+                                                      &error_fatal);
+
+                    visit_type_CompatPolicy(v, NULL, &opts, &error_fatal);
+                    QAPI_CLONE_MEMBERS(CompatPolicy, &compat_policy, opts);
+
+                    qapi_free_CompatPolicy(opts);
+                    visit_free(v);
+                    break;
+                }
             case QEMU_OPTION_msg:
                 opts = qemu_opts_parse_noisily(qemu_find_opts("msg"), optarg,
                                                false);
diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
index 268078ad2c..72900dc2ec 100644
--- a/storage-daemon/qemu-storage-daemon.c
+++ b/storage-daemon/qemu-storage-daemon.c
@@ -137,8 +137,6 @@ extern QemuOptsList qemu_chardev_opts;
 static void init_qmp_commands(void)
 {
     qmp_init_marshal(&qmp_commands);
-    qmp_register_command(&qmp_commands, "query-qmp-schema",
-                         qmp_query_qmp_schema, QCO_ALLOW_PRECONFIG);
 
     QTAILQ_INIT(&qmp_cap_negotiation_commands);
     qmp_register_command(&qmp_cap_negotiation_commands, "qmp_capabilities",
diff --git a/stubs/meson.build b/stubs/meson.build
index a054d5877f..8a3e804cf0 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -34,7 +34,6 @@ stub_ss.add(files('ram-block.c'))
 stub_ss.add(files('ramfb.c'))
 stub_ss.add(files('replay.c'))
 stub_ss.add(files('runstate-check.c'))
-stub_ss.add(files('set-fd-handler.c'))
 stub_ss.add(files('sysbus.c'))
 stub_ss.add(files('target-get-monitor-def.c'))
 stub_ss.add(files('target-monitor-defs.c'))
diff --git a/stubs/set-fd-handler.c b/stubs/set-fd-handler.c
deleted file mode 100644
index bff7e0a45a..0000000000
--- a/stubs/set-fd-handler.c
+++ /dev/null
@@ -1,10 +0,0 @@
-#include "qemu/osdep.h"
-#include "qemu/main-loop.h"
-
-void qemu_set_fd_handler(int fd,
-                         IOHandler *fd_read,
-                         IOHandler *fd_write,
-                         void *opaque)
-{
-    abort();
-}
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index 63f92adf68..12ec588b52 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -299,14 +299,15 @@
   'features': [ 'feature1' ] }
 
 { 'command': 'test-features0',
-  'data': { 'fs0': 'FeatureStruct0',
-            'fs1': 'FeatureStruct1',
-            'fs2': 'FeatureStruct2',
-            'fs3': 'FeatureStruct3',
-            'fs4': 'FeatureStruct4',
-            'cfs1': 'CondFeatureStruct1',
-            'cfs2': 'CondFeatureStruct2',
-            'cfs3': 'CondFeatureStruct3' },
+  'data': { '*fs0': 'FeatureStruct0',
+            '*fs1': 'FeatureStruct1',
+            '*fs2': 'FeatureStruct2',
+            '*fs3': 'FeatureStruct3',
+            '*fs4': 'FeatureStruct4',
+            '*cfs1': 'CondFeatureStruct1',
+            '*cfs2': 'CondFeatureStruct2',
+            '*cfs3': 'CondFeatureStruct3' },
+  'returns': 'FeatureStruct1',
   'features': [] }
 
 { 'command': 'test-command-features1',
@@ -323,5 +324,8 @@
   'features': [ { 'name': 'feature1', 'if': [ 'defined(TEST_IF_COND_1)',
                                               'defined(TEST_IF_COND_2)'] } ] }
 
+{ 'event': 'TEST-EVENT-FEATURES0',
+  'data': 'FeatureStruct1' }
+
 { 'event': 'TEST-EVENT-FEATURES1',
   'features': [ 'deprecated' ] }
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index 3b1387d9f1..f5741df97f 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -409,15 +409,15 @@ alternate FeatureAlternate1
     case eins: FeatureStruct1
     feature feature1
 object q_obj_test-features0-arg
-    member fs0: FeatureStruct0 optional=False
-    member fs1: FeatureStruct1 optional=False
-    member fs2: FeatureStruct2 optional=False
-    member fs3: FeatureStruct3 optional=False
-    member fs4: FeatureStruct4 optional=False
-    member cfs1: CondFeatureStruct1 optional=False
-    member cfs2: CondFeatureStruct2 optional=False
-    member cfs3: CondFeatureStruct3 optional=False
-command test-features0 q_obj_test-features0-arg -> None
+    member fs0: FeatureStruct0 optional=True
+    member fs1: FeatureStruct1 optional=True
+    member fs2: FeatureStruct2 optional=True
+    member fs3: FeatureStruct3 optional=True
+    member fs4: FeatureStruct4 optional=True
+    member cfs1: CondFeatureStruct1 optional=True
+    member cfs2: CondFeatureStruct2 optional=True
+    member cfs3: CondFeatureStruct3 optional=True
+command test-features0 q_obj_test-features0-arg -> FeatureStruct1
     gen=True success_response=True boxed=False oob=False preconfig=False
 command test-command-features1 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
@@ -440,6 +440,8 @@ command test-command-cond-features3 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
     feature feature1
         if ['defined(TEST_IF_COND_1)', 'defined(TEST_IF_COND_2)']
+event TEST-EVENT-FEATURES0 FeatureStruct1
+    boxed=False
 event TEST-EVENT-FEATURES1 None
     boxed=False
     feature deprecated
diff --git a/tests/unit/test-qmp-cmds.c b/tests/unit/test-qmp-cmds.c
index d3413bfef0..266db074b4 100644
--- a/tests/unit/test-qmp-cmds.c
+++ b/tests/unit/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"
@@ -49,12 +50,17 @@ 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_new0(FeatureStruct1, 1);
 }
 
 void qmp_test_command_features1(Error **errp)
@@ -275,6 +281,75 @@ static void test_dispatch_cmd_io(void)
     qobject_unref(ret3);
 }
 
+static void test_dispatch_cmd_deprecated(void)
+{
+    const char *cmd = "{ 'execute': 'test-command-features1' }";
+    QDict *ret;
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    /* accept */
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 0);
+    qobject_unref(ret);
+
+    compat_policy.has_deprecated_input = true;
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_ACCEPT;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 0);
+    qobject_unref(ret);
+
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_REJECT;
+    do_qmp_dispatch_error(false, ERROR_CLASS_COMMAND_NOT_FOUND, cmd);
+}
+
+static void test_dispatch_cmd_arg_deprecated(void)
+{
+    const char *cmd = "{ 'execute': 'test-features0',"
+        " 'arguments': { 'fs1': { 'foo': 42 } } }";
+    QDict *ret;
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    /* accept */
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.has_deprecated_input = true;
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_ACCEPT;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_REJECT;
+    do_qmp_dispatch_error(false, ERROR_CLASS_GENERIC_ERROR, cmd);
+}
+
+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)
 {
@@ -349,6 +424,12 @@ 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_deprecated",
+                    test_dispatch_cmd_deprecated);
+    g_test_add_func("/qmp/dispatch_cmd_arg_deprecated",
+                    test_dispatch_cmd_arg_deprecated);
+    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/tests/unit/test-qmp-event.c b/tests/unit/test-qmp-event.c
index 7dd0053190..047f44ff9a 100644
--- a/tests/unit/test-qmp-event.c
+++ b/tests/unit/test-qmp-event.c
@@ -14,6 +14,7 @@
 #include "qemu/osdep.h"
 
 #include "qemu-common.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qbool.h"
 #include "qapi/qmp/qdict.h"
@@ -140,6 +141,44 @@ static void test_event_d(TestEventData *data,
     qobject_unref(data->expect);
 }
 
+static void test_event_deprecated(TestEventData *data, const void *unused)
+{
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES1' }");
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    qapi_event_send_test_event_features1();
+    g_assert(data->emitted);
+
+    compat_policy.has_deprecated_output = true;
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
+    data->emitted = false;
+    qapi_event_send_test_event_features1();
+    g_assert(!data->emitted);
+
+    qobject_unref(data->expect);
+}
+
+static void test_event_deprecated_data(TestEventData *data, const void *unused)
+{
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES0',"
+                                           " 'data': { 'foo': 42 } }");
+    qapi_event_send_test_event_features0(42);
+    g_assert(data->emitted);
+
+    qobject_unref(data->expect);
+
+    compat_policy.has_deprecated_output = true;
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES0' }");
+    qapi_event_send_test_event_features0(42);
+    g_assert(data->emitted);
+
+    qobject_unref(data->expect);
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -148,6 +187,8 @@ int main(int argc, char **argv)
     event_test_add("/event/event_b", test_event_b);
     event_test_add("/event/event_c", test_event_c);
     event_test_add("/event/event_d", test_event_d);
+    event_test_add("/event/deprecated", test_event_deprecated);
+    event_test_add("/event/deprecated_data", test_event_deprecated_data);
     g_test_run();
 
     return 0;
diff --git a/tests/unit/test-util-sockets.c b/tests/unit/test-util-sockets.c
index 67486055ed..72b9246529 100644
--- a/tests/unit/test-util-sockets.c
+++ b/tests/unit/test-util-sockets.c
@@ -73,6 +73,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
  * otherwise we get duplicate syms at link time.
  */
 Monitor *monitor_cur(void) { return cur_mon; }
+Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { abort(); }
 int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap) { abort(); }
 
 #ifndef _WIN32