Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2021-10-29' into staging

QAPI patches patches for 2021-10-29

# gpg: Signature made Fri 29 Oct 2021 12:28:53 PM PDT
# 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]

* remotes/armbru/tags/pull-qapi-2021-10-29:
  qapi: Extend -compat to set policy for unstable interfaces
  qapi: Factor out compat_policy_input_ok()
  qapi: Generalize enum member policy checking
  qapi: Generalize command policy checking
  qapi: Generalize struct member policy checking
  qapi: Tools for sets of special feature flags in generated code
  qapi: Eliminate QCO_NO_OPTIONS for a slight simplification
  qapi: Mark unstable QMP parts with feature 'unstable'
  qapi: New special feature flag "unstable"

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

30 files changed, 354 insertions, 165 deletions

diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
index 4071c9074a..38f2d7aad3 100644
--- a/docs/devel/qapi-code-gen.rst
+++ b/docs/devel/qapi-code-gen.rst
@@ -713,6 +713,10 @@ member as deprecated.  It is not supported elsewhere so far.
 Interfaces so marked may be withdrawn in future releases in accordance
 with QEMU's deprecation policy.
 
+Feature "unstable" marks a command, event, enum value, or struct
+member as unstable.  It is not supported elsewhere so far.  Interfaces
+so marked may be withdrawn or changed incompatibly in future releases.
+
 
 Naming rules and reserved names
 -------------------------------
@@ -746,9 +750,8 @@ Member name ``u`` and names starting with ``has-`` or ``has_`` are reserved
 for the generator, which uses them for unions and for tracking
 optional members.
 
-Any name (command, event, type, member, or enum value) beginning with
-``x-`` is marked experimental, and may be withdrawn or changed
-incompatibly in a future release.
+Names beginning with ``x-`` used to signify "experimental".  This
+convention has been replaced by special feature "unstable".
 
 Pragmas ``command-name-exceptions`` and ``member-name-exceptions`` let
 you violate naming rules.  Use for new code is strongly discouraged. See
diff --git a/include/qapi/compat-policy.h b/include/qapi/compat-policy.h
index 1083f95122..8b7b25c0b5 100644
--- a/include/qapi/compat-policy.h
+++ b/include/qapi/compat-policy.h
@@ -13,10 +13,17 @@
 #ifndef QAPI_COMPAT_POLICY_H
 #define QAPI_COMPAT_POLICY_H
 
+#include "qapi/error.h"
 #include "qapi/qapi-types-compat.h"
 
 extern CompatPolicy compat_policy;
 
+bool compat_policy_input_ok(unsigned special_features,
+                            const CompatPolicy *policy,
+                            ErrorClass error_class,
+                            const char *kind, const char *name,
+                            Error **errp);
+
 /*
  * Create a QObject input visitor for @obj for use with QMP
  *
diff --git a/include/qapi/qmp/dispatch.h b/include/qapi/qmp/dispatch.h
index 075203dc67..1e4240fd0d 100644
--- a/include/qapi/qmp/dispatch.h
+++ b/include/qapi/qmp/dispatch.h
@@ -21,12 +21,10 @@ typedef void (QmpCommandFunc)(QDict *, QObject **, Error **);
 
 typedef enum QmpCommandOptions
 {
-    QCO_NO_OPTIONS            =  0x0,
     QCO_NO_SUCCESS_RESP       =  (1U << 0),
     QCO_ALLOW_OOB             =  (1U << 1),
     QCO_ALLOW_PRECONFIG       =  (1U << 2),
     QCO_COROUTINE             =  (1U << 3),
-    QCO_DEPRECATED            =  (1U << 4),
 } QmpCommandOptions;
 
 typedef struct QmpCommand
@@ -35,6 +33,7 @@ typedef struct QmpCommand
     /* Runs in coroutine context if QCO_COROUTINE is set */
     QmpCommandFunc *fn;
     QmpCommandOptions options;
+    unsigned special_features;
     QTAILQ_ENTRY(QmpCommand) node;
     bool enabled;
     const char *disable_reason;
@@ -43,7 +42,8 @@ typedef struct QmpCommand
 typedef QTAILQ_HEAD(QmpCommandList, QmpCommand) QmpCommandList;
 
 void qmp_register_command(QmpCommandList *cmds, const char *name,
-                          QmpCommandFunc *fn, QmpCommandOptions options);
+                          QmpCommandFunc *fn, QmpCommandOptions options,
+                          unsigned special_features);
 const QmpCommand *qmp_find_command(const QmpCommandList *cmds,
                                    const char *name);
 void qmp_disable_command(QmpCommandList *cmds, const char *name,
diff --git a/include/qapi/util.h b/include/qapi/util.h
index 257c600f99..81a2b13a33 100644
--- a/include/qapi/util.h
+++ b/include/qapi/util.h
@@ -11,12 +11,14 @@
 #ifndef QAPI_UTIL_H
 #define QAPI_UTIL_H
 
-/* QEnumLookup flags */
-#define QAPI_ENUM_DEPRECATED 1
+typedef enum {
+    QAPI_DEPRECATED,
+    QAPI_UNSTABLE,
+} QapiSpecialFeature;
 
 typedef struct QEnumLookup {
     const char *const *array;
-    const unsigned char *const flags;
+    const unsigned char *const special_features;
     const int size;
 } QEnumLookup;
 
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 72b6537bef..2badec5ba4 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -114,10 +114,12 @@ struct Visitor
     void (*optional)(Visitor *v, const char *name, bool *present);
 
     /* Optional */
-    bool (*deprecated_accept)(Visitor *v, const char *name, Error **errp);
+    bool (*policy_reject)(Visitor *v, const char *name,
+                          unsigned special_features, Error **errp);
 
     /* Optional */
-    bool (*deprecated)(Visitor *v, const char *name);
+    bool (*policy_skip)(Visitor *v, const char *name,
+                        unsigned special_features);
 
     /* Must be set */
     VisitorType type;
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index dcb96018a9..d53a84c9ba 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -461,22 +461,31 @@ void visit_end_alternate(Visitor *v, void **obj);
 bool visit_optional(Visitor *v, const char *name, bool *present);
 
 /*
- * Should we reject deprecated member @name?
+ * Should we reject member @name due to policy?
+ *
+ * @special_features is the member's special features encoded as a
+ * bitset of QapiSpecialFeature.
  *
  * @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);
+bool visit_policy_reject(Visitor *v, const char *name,
+                         unsigned special_features, Error **errp);
 
 /*
- * Should we visit deprecated member @name?
+ *
+ * Should we skip member @name due to policy?
+ *
+ * @special_features is the member's special features encoded as a
+ * bitset of QapiSpecialFeature.
  *
  * @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);
+bool visit_policy_skip(Visitor *v, const char *name,
+                       unsigned special_features);
 
 /*
  * Set policy for handling deprecated management interfaces.
diff --git a/monitor/misc.c b/monitor/misc.c
index ffe7966870..c2d227a07c 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -230,12 +230,13 @@ static void monitor_init_qmp_commands(void)
 
     qmp_init_marshal(&qmp_commands);
 
-    qmp_register_command(&qmp_commands, "device_add", qmp_device_add,
-                         QCO_NO_OPTIONS);
+    qmp_register_command(&qmp_commands, "device_add",
+                         qmp_device_add, 0, 0);
 
     QTAILQ_INIT(&qmp_cap_negotiation_commands);
     qmp_register_command(&qmp_cap_negotiation_commands, "qmp_capabilities",
-                         qmp_marshal_qmp_capabilities, QCO_ALLOW_PRECONFIG);
+                         qmp_marshal_qmp_capabilities,
+                         QCO_ALLOW_PRECONFIG, 0);
 }
 
 /* Set the current CPU defined by the user. Callers must hold BQL. */
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 6d3217abb6..ce2c1352cb 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1438,6 +1438,9 @@
 #
 # @x-perf: Performance options. (Since 6.0)
 #
+# Features:
+# @unstable: Member @x-perf is experimental.
+#
 # Note: @on-source-error and @on-target-error only affect background
 #       I/O.  If an error occurs during a guest write request, the device's
 #       rerror/werror actions will be used.
@@ -1452,7 +1455,9 @@
             '*on-source-error': 'BlockdevOnError',
             '*on-target-error': 'BlockdevOnError',
             '*auto-finalize': 'bool', '*auto-dismiss': 'bool',
-            '*filter-node-name': 'str', '*x-perf': 'BackupPerf'  } }
+            '*filter-node-name': 'str',
+            '*x-perf': { 'type': 'BackupPerf',
+                         'features': [ 'unstable' ] } } }
 
 ##
 # @DriveBackup:
@@ -1916,9 +1921,13 @@
 #
 # Get the block graph.
 #
+# Features:
+# @unstable: This command is meant for debugging.
+#
 # Since: 4.0
 ##
-{ 'command': 'x-debug-query-block-graph', 'returns': 'XDbgBlockGraph' }
+{ 'command': 'x-debug-query-block-graph', 'returns': 'XDbgBlockGraph',
+  'features': [ 'unstable' ] }
 
 ##
 # @drive-mirror:
@@ -2257,6 +2266,9 @@
 #
 # Get bitmap SHA256.
 #
+# Features:
+# @unstable: This command is meant for debugging.
+#
 # Returns: - BlockDirtyBitmapSha256 on success
 #          - If @node is not a valid block device, DeviceNotFound
 #          - If @name is not found or if hashing has failed, GenericError with an
@@ -2265,7 +2277,8 @@
 # Since: 2.10
 ##
 { 'command': 'x-debug-block-dirty-bitmap-sha256',
-  'data': 'BlockDirtyBitmap', 'returns': 'BlockDirtyBitmapSha256' }
+  'data': 'BlockDirtyBitmap', 'returns': 'BlockDirtyBitmapSha256',
+  'features': [ 'unstable' ] }
 
 ##
 # @blockdev-mirror:
@@ -2495,27 +2508,57 @@
 #
 # Properties for throttle-group objects.
 #
-# The options starting with x- are aliases for the same key without x- in
-# the @limits object. As indicated by the x- prefix, this is not a stable
-# interface and may be removed or changed incompatibly in the future. Use
-# @limits for a supported stable interface.
-#
 # @limits: limits to apply for this throttle group
 #
+# Features:
+# @unstable: All members starting with x- are aliases for the same key
+#            without x- in the @limits object.  This is not a stable
+#            interface and may be removed or changed incompatibly in
+#            the future.  Use @limits for a supported stable
+#            interface.
+#
 # Since: 2.11
 ##
 { 'struct': 'ThrottleGroupProperties',
   'data': { '*limits': 'ThrottleLimits',
-            '*x-iops-total' : 'int', '*x-iops-total-max' : 'int',
-            '*x-iops-total-max-length' : 'int', '*x-iops-read' : 'int',
-            '*x-iops-read-max' : 'int', '*x-iops-read-max-length' : 'int',
-            '*x-iops-write' : 'int', '*x-iops-write-max' : 'int',
-            '*x-iops-write-max-length' : 'int', '*x-bps-total' : 'int',
-            '*x-bps-total-max' : 'int', '*x-bps-total-max-length' : 'int',
-            '*x-bps-read' : 'int', '*x-bps-read-max' : 'int',
-            '*x-bps-read-max-length' : 'int', '*x-bps-write' : 'int',
-            '*x-bps-write-max' : 'int', '*x-bps-write-max-length' : 'int',
-            '*x-iops-size' : 'int' } }
+            '*x-iops-total': { 'type': 'int',
+                               'features': [ 'unstable' ] },
+            '*x-iops-total-max': { 'type': 'int',
+                                   'features': [ 'unstable' ] },
+            '*x-iops-total-max-length': { 'type': 'int',
+                                          'features': [ 'unstable' ] },
+            '*x-iops-read': { 'type': 'int',
+                              'features': [ 'unstable' ] },
+            '*x-iops-read-max': { 'type': 'int',
+                                  'features': [ 'unstable' ] },
+            '*x-iops-read-max-length': { 'type': 'int',
+                                         'features': [ 'unstable' ] },
+            '*x-iops-write': { 'type': 'int',
+                               'features': [ 'unstable' ] },
+            '*x-iops-write-max': { 'type': 'int',
+                                   'features': [ 'unstable' ] },
+            '*x-iops-write-max-length': { 'type': 'int',
+                                          'features': [ 'unstable' ] },
+            '*x-bps-total': { 'type': 'int',
+                              'features': [ 'unstable' ] },
+            '*x-bps-total-max': { 'type': 'int',
+                                  'features': [ 'unstable' ] },
+            '*x-bps-total-max-length': { 'type': 'int',
+                                         'features': [ 'unstable' ] },
+            '*x-bps-read': { 'type': 'int',
+                             'features': [ 'unstable' ] },
+            '*x-bps-read-max': { 'type': 'int',
+                                 'features': [ 'unstable' ] },
+            '*x-bps-read-max-length': { 'type': 'int',
+                                        'features': [ 'unstable' ] },
+            '*x-bps-write': { 'type': 'int',
+                              'features': [ 'unstable' ] },
+            '*x-bps-write-max': { 'type': 'int',
+                                  'features': [ 'unstable' ] },
+            '*x-bps-write-max-length': { 'type': 'int',
+                                         'features': [ 'unstable' ] },
+            '*x-iops-size': { 'type': 'int',
+                              'features': [ 'unstable' ] } } }
 
 ##
 # @block-stream:
@@ -2916,6 +2959,7 @@
 #                          read-only when the last writer is detached. This
 #                          allows giving QEMU write permissions only on demand
 #                          when an operation actually needs write access.
+# @unstable: Member x-check-cache-dropped is meant for debugging.
 #
 # Since: 2.9
 ##
@@ -2926,7 +2970,8 @@
             '*aio': 'BlockdevAioOptions',
             '*drop-cache': {'type': 'bool',
                             'if': 'CONFIG_LINUX'},
-            '*x-check-cache-dropped': 'bool' },
+            '*x-check-cache-dropped': { 'type': 'bool',
+                                        'features': [ 'unstable' ] } },
   'features': [ { 'name': 'dynamic-auto-read-only',
                   'if': 'CONFIG_POSIX' } ] }
 
@@ -4041,13 +4086,16 @@
 #                   future requests before a successful reconnect will
 #                   immediately fail. Default 0 (Since 4.2)
 #
+# Features:
+# @unstable: Member @x-dirty-bitmap is experimental.
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsNbd',
   'data': { 'server': 'SocketAddress',
             '*export': 'str',
             '*tls-creds': 'str',
-            '*x-dirty-bitmap': 'str',
+            '*x-dirty-bitmap': { 'type': 'str', 'features': [ 'unstable' ] },
             '*reconnect-delay': 'uint32' } }
 
 ##
@@ -4865,13 +4913,17 @@
 #                   and replacement of an active keyslot
 #                   (possible loss of data if IO error happens)
 #
+# Features:
+# @unstable: This command is experimental.
+#
 # Since: 5.1
 ##
 { 'command': 'x-blockdev-amend',
   'data': { 'job-id': 'str',
             'node-name': 'str',
             'options': 'BlockdevAmendOptions',
-            '*force': 'bool' } }
+            '*force': 'bool' },
+  'features': [ 'unstable' ] }
 
 ##
 # @BlockErrorAction:
@@ -5242,16 +5294,18 @@
 #
 # @node: the name of the node that will be added.
 #
-# Note: this command is experimental, and its API is not stable. It
-#       does not support all kinds of operations, all kinds of children, nor
-#       all block drivers.
+# Features:
+# @unstable: This command is experimental, and its API is not stable.  It
+#            does not support all kinds of operations, all kinds of
+#            children, nor all block drivers.
 #
-#       FIXME Removing children from a quorum node means introducing gaps in the
-#       child indices. This cannot be represented in the 'children' list of
-#       BlockdevOptionsQuorum, as returned by .bdrv_refresh_filename().
+#            FIXME Removing children from a quorum node means introducing
+#            gaps in the child indices. This cannot be represented in the
+#            'children' list of BlockdevOptionsQuorum, as returned by
+#            .bdrv_refresh_filename().
 #
-#       Warning: The data in a new quorum child MUST be consistent with that of
-#       the rest of the array.
+#            Warning: The data in a new quorum child MUST be consistent
+#            with that of the rest of the array.
 #
 # Since: 2.7
 #
@@ -5280,7 +5334,8 @@
 { 'command': 'x-blockdev-change',
   'data' : { 'parent': 'str',
              '*child': 'str',
-             '*node': 'str' } }
+             '*node': 'str' },
+  'features': [ 'unstable' ] }
 
 ##
 # @x-blockdev-set-iothread:
@@ -5297,8 +5352,9 @@
 # @force: true if the node and its children should be moved when a BlockBackend
 #         is already attached
 #
-# Note: this command is experimental and intended for test cases that need
-#       control over IOThreads only.
+# Features:
+# @unstable: This command is experimental and intended for test cases that
+#            need control over IOThreads only.
 #
 # Since: 2.12
 #
@@ -5320,7 +5376,8 @@
 { 'command': 'x-blockdev-set-iothread',
   'data' : { 'node-name': 'str',
              'iothread': 'StrOrNull',
-             '*force': 'bool' } }
+             '*force': 'bool' },
+  'features': [ 'unstable' ] }
 
 ##
 # @QuorumOpType:
diff --git a/qapi/compat.json b/qapi/compat.json
index 74a8493d3d..dd7261ae2a 100644
--- a/qapi/compat.json
+++ b/qapi/compat.json
@@ -47,9 +47,15 @@
 #
 # @deprecated-input: how to handle deprecated input (default 'accept')
 # @deprecated-output: how to handle deprecated output (default 'accept')
+# @unstable-input: how to handle unstable input (default 'accept')
+#                  (since 6.2)
+# @unstable-output: how to handle unstable output (default 'accept')
+#                   (since 6.2)
 #
 # Since: 6.0
 ##
 { 'struct': 'CompatPolicy',
   'data': { '*deprecated-input': 'CompatPolicyInput',
-            '*deprecated-output': 'CompatPolicyOutput' } }
+            '*deprecated-output': 'CompatPolicyOutput',
+            '*unstable-input': 'CompatPolicyInput',
+            '*unstable-output': 'CompatPolicyOutput' } }
diff --git a/qapi/migration.json b/qapi/migration.json
index 88f07baedd..9aa8bc5759 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -452,14 +452,20 @@
 #                       procedure starts. The VM RAM is saved with running VM.
 #                       (since 6.0)
 #
+# Features:
+# @unstable: Members @x-colo and @x-ignore-shared are experimental.
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
+           'compress', 'events', 'postcopy-ram',
+           { 'name': 'x-colo', 'features': [ 'unstable' ] },
+           'release-ram',
            'block', 'return-path', 'pause-before-switchover', 'multifd',
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
-           'x-ignore-shared', 'validate-uuid', 'background-snapshot'] }
+           { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
+           'validate-uuid', 'background-snapshot'] }
 
 ##
 # @MigrationCapabilityStatus:
@@ -743,6 +749,9 @@
 #                        block device name if there is one, and to their node name
 #                        otherwise. (Since 5.2)
 #
+# Features:
+# @unstable: Member @x-checkpoint-delay is experimental.
+#
 # Since: 2.4
 ##
 { 'enum': 'MigrationParameter',
@@ -753,7 +762,9 @@
            'cpu-throttle-initial', 'cpu-throttle-increment',
            'cpu-throttle-tailslow',
            'tls-creds', 'tls-hostname', 'tls-authz', 'max-bandwidth',
-           'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
+           'downtime-limit',
+           { 'name': 'x-checkpoint-delay', 'features': [ 'unstable' ] },
+           'block-incremental',
            'multifd-channels',
            'xbzrle-cache-size', 'max-postcopy-bandwidth',
            'max-cpu-throttle', 'multifd-compression',
@@ -903,6 +914,9 @@
 #                        block device name if there is one, and to their node name
 #                        otherwise. (Since 5.2)
 #
+# Features:
+# @unstable: Member @x-checkpoint-delay is experimental.
+#
 # Since: 2.4
 ##
 # TODO either fuse back into MigrationParameters, or make
@@ -925,7 +939,8 @@
             '*tls-authz': 'StrOrNull',
             '*max-bandwidth': 'size',
             '*downtime-limit': 'uint64',
-            '*x-checkpoint-delay': 'uint32',
+            '*x-checkpoint-delay': { 'type': 'uint32',
+                                     'features': [ 'unstable' ] },
             '*block-incremental': 'bool',
             '*multifd-channels': 'uint8',
             '*xbzrle-cache-size': 'size',
@@ -1099,6 +1114,9 @@
 #                        block device name if there is one, and to their node name
 #                        otherwise. (Since 5.2)
 #
+# Features:
+# @unstable: Member @x-checkpoint-delay is experimental.
+#
 # Since: 2.4
 ##
 { 'struct': 'MigrationParameters',
@@ -1119,7 +1137,8 @@
             '*tls-authz': 'str',
             '*max-bandwidth': 'size',
             '*downtime-limit': 'uint64',
-            '*x-checkpoint-delay': 'uint32',
+            '*x-checkpoint-delay': { 'type': 'uint32',
+                                     'features': [ 'unstable' ] },
             '*block-incremental': 'bool',
             '*multifd-channels': 'uint8',
             '*xbzrle-cache-size': 'size',
@@ -1351,6 +1370,9 @@
 # If sent to the Secondary, the Secondary side will run failover work,
 # then takes over server operation to become the service VM.
 #
+# Features:
+# @unstable: This command is experimental.
+#
 # Since: 2.8
 #
 # Example:
@@ -1359,7 +1381,8 @@
 # <- { "return": {} }
 #
 ##
-{ 'command': 'x-colo-lost-heartbeat' }
+{ 'command': 'x-colo-lost-heartbeat',
+  'features': [ 'unstable' ] }
 
 ##
 # @migrate_cancel:
diff --git a/qapi/misc.json b/qapi/misc.json
index 5c2ca3b556..358548abe1 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -185,6 +185,9 @@
 # available during the preconfig state (i.e. when the --preconfig command
 # line option was in use).
 #
+# Features:
+# @unstable: This command is experimental.
+#
 # Since 3.0
 #
 # Returns: nothing
@@ -195,7 +198,8 @@
 # <- { "return": {} }
 #
 ##
-{ 'command': 'x-exit-preconfig', 'allow-preconfig': true }
+{ 'command': 'x-exit-preconfig', 'allow-preconfig': true,
+  'features': [ 'unstable' ] }
 
 ##
 # @human-monitor-command:
diff --git a/qapi/qapi-forward-visitor.c b/qapi/qapi-forward-visitor.c
index a4b111e22a..4ea7e0bec3 100644
--- a/qapi/qapi-forward-visitor.c
+++ b/qapi/qapi-forward-visitor.c
@@ -246,25 +246,27 @@ static void forward_field_optional(Visitor *v, const char *name, bool *present)
     visit_optional(ffv->target, name, present);
 }
 
-static bool forward_field_deprecated_accept(Visitor *v, const char *name,
-                                            Error **errp)
+static bool forward_field_policy_reject(Visitor *v, const char *name,
+                                        unsigned special_features,
+                                        Error **errp)
 {
     ForwardFieldVisitor *ffv = to_ffv(v);
 
     if (!forward_field_translate_name(ffv, &name, errp)) {
-        return false;
+        return true;
     }
-    return visit_deprecated_accept(ffv->target, name, errp);
+    return visit_policy_reject(ffv->target, name, special_features, errp);
 }
 
-static bool forward_field_deprecated(Visitor *v, const char *name)
+static bool forward_field_policy_skip(Visitor *v, const char *name,
+                                      unsigned special_features)
 {
     ForwardFieldVisitor *ffv = to_ffv(v);
 
     if (!forward_field_translate_name(ffv, &name, NULL)) {
-        return false;
+        return true;
     }
-    return visit_deprecated(ffv->target, name);
+    return visit_policy_skip(ffv->target, name, special_features);
 }
 
 static void forward_field_complete(Visitor *v, void *opaque)
@@ -313,8 +315,8 @@ Visitor *visitor_forward_field(Visitor *target, const char *from, const char *to
     v->visitor.type_any = forward_field_type_any;
     v->visitor.type_null = forward_field_type_null;
     v->visitor.optional = forward_field_optional;
-    v->visitor.deprecated_accept = forward_field_deprecated_accept;
-    v->visitor.deprecated = forward_field_deprecated;
+    v->visitor.policy_reject = forward_field_policy_reject;
+    v->visitor.policy_skip = forward_field_policy_skip;
     v->visitor.complete = forward_field_complete;
     v->visitor.free = forward_field_free;
 
diff --git a/qapi/qapi-util.c b/qapi/qapi-util.c
index 3c24bb3d45..fda7044539 100644
--- a/qapi/qapi-util.c
+++ b/qapi/qapi-util.c
@@ -11,10 +11,53 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qemu/ctype.h"
 #include "qapi/qmp/qerror.h"
 
+CompatPolicy compat_policy;
+
+static bool compat_policy_input_ok1(const char *adjective,
+                                    CompatPolicyInput policy,
+                                    ErrorClass error_class,
+                                    const char *kind, const char *name,
+                                    Error **errp)
+{
+    switch (policy) {
+    case COMPAT_POLICY_INPUT_ACCEPT:
+        return true;
+    case COMPAT_POLICY_INPUT_REJECT:
+        error_set(errp, error_class, "%s %s %s disabled by policy",
+                  adjective, kind, name);
+        return false;
+    case COMPAT_POLICY_INPUT_CRASH:
+    default:
+        abort();
+    }
+}
+
+bool compat_policy_input_ok(unsigned special_features,
+                            const CompatPolicy *policy,
+                            ErrorClass error_class,
+                            const char *kind, const char *name,
+                            Error **errp)
+{
+    if ((special_features & 1u << QAPI_DEPRECATED)
+        && !compat_policy_input_ok1("Deprecated",
+                                    policy->deprecated_input,
+                                    error_class, kind, name, errp)) {
+        return false;
+    }
+    if ((special_features & (1u << QAPI_UNSTABLE))
+        && !compat_policy_input_ok1("Unstable",
+                                    policy->unstable_input,
+                                    error_class, kind, name, errp)) {
+        return false;
+    }
+    return true;
+}
+
 const char *qapi_enum_lookup(const QEnumLookup *lookup, int val)
 {
     assert(val >= 0 && val < lookup->size);
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 617ef3fa46..6c13510a2b 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -13,6 +13,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
 #include "qapi/visitor.h"
@@ -139,22 +140,24 @@ bool visit_optional(Visitor *v, const char *name, bool *present)
     return *present;
 }
 
-bool visit_deprecated_accept(Visitor *v, const char *name, Error **errp)
+bool visit_policy_reject(Visitor *v, const char *name,
+                         unsigned special_features, Error **errp)
 {
-    trace_visit_deprecated_accept(v, name);
-    if (v->deprecated_accept) {
-        return v->deprecated_accept(v, name, errp);
+    trace_visit_policy_reject(v, name);
+    if (v->policy_reject) {
+        return v->policy_reject(v, name, special_features, errp);
     }
-    return true;
+    return false;
 }
 
-bool visit_deprecated(Visitor *v, const char *name)
+bool visit_policy_skip(Visitor *v, const char *name,
+                       unsigned special_features)
 {
-    trace_visit_deprecated(v, name);
-    if (v->deprecated) {
-        return v->deprecated(v, name);
+    trace_visit_policy_skip(v, name);
+    if (v->policy_skip) {
+        return v->policy_skip(v, name, special_features);
     }
-    return true;
+    return false;
 }
 
 void visit_set_policy(Visitor *v, CompatPolicy *policy)
@@ -406,18 +409,12 @@ static bool input_type_enum(Visitor *v, const char *name, int *obj,
         return false;
     }
 
-    if (lookup->flags && (lookup->flags[value] & QAPI_ENUM_DEPRECATED)) {
-        switch (v->compat_policy.deprecated_input) {
-        case COMPAT_POLICY_INPUT_ACCEPT:
-            break;
-        case COMPAT_POLICY_INPUT_REJECT:
-            error_setg(errp, "Deprecated value '%s' disabled by policy",
-                       enum_str);
-            return false;
-        case COMPAT_POLICY_INPUT_CRASH:
-        default:
-            abort();
-        }
+    if (lookup->special_features
+        && !compat_policy_input_ok(lookup->special_features[value],
+                                   &v->compat_policy,
+                                   ERROR_CLASS_GENERIC_ERROR,
+                                   "value", enum_str, errp)) {
+        return false;
     }
 
     *obj = value;
diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 7e943a0af5..d378bccac7 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -26,8 +26,6 @@
 #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);
@@ -176,19 +174,10 @@ 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 (!compat_policy_input_ok(cmd->special_features, &compat_policy,
+                                ERROR_CLASS_COMMAND_NOT_FOUND,
+                                "command", command, &err)) {
+        goto out;
     }
     if (!cmd->enabled) {
         error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
diff --git a/qapi/qmp-registry.c b/qapi/qmp-registry.c
index f78c064aae..485bc5e6fc 100644
--- a/qapi/qmp-registry.c
+++ b/qapi/qmp-registry.c
@@ -16,7 +16,8 @@
 #include "qapi/qmp/dispatch.h"
 
 void qmp_register_command(QmpCommandList *cmds, const char *name,
-                          QmpCommandFunc *fn, QmpCommandOptions options)
+                          QmpCommandFunc *fn, QmpCommandOptions options,
+                          unsigned special_features)
 {
     QmpCommand *cmd = g_malloc0(sizeof(*cmd));
 
@@ -27,6 +28,7 @@ void qmp_register_command(QmpCommandList *cmds, const char *name,
     cmd->fn = fn;
     cmd->enabled = true;
     cmd->options = options;
+    cmd->special_features = special_features;
     QTAILQ_INSERT_TAIL(cmds, cmd, node);
 }
 
diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index 71b24a4429..f0b4c7ca9d 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"
@@ -662,20 +663,13 @@ 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)
+static bool qobject_input_policy_reject(Visitor *v, const char *name,
+                                        unsigned special_features,
+                                        Error **errp)
 {
-    switch (v->compat_policy.deprecated_input) {
-    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();
-    }
+    return !compat_policy_input_ok(special_features, &v->compat_policy,
+                                   ERROR_CLASS_GENERIC_ERROR,
+                                   "parameter", name, errp);
 }
 
 static void qobject_input_free(Visitor *v)
@@ -712,7 +706,7 @@ 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.policy_reject = qobject_input_policy_reject;
     v->visitor.free = qobject_input_free;
 
     v->root = qobject_ref(obj);
diff --git a/qapi/qobject-output-visitor.c b/qapi/qobject-output-visitor.c
index 9b7f510036..74770edd73 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"
@@ -208,9 +209,15 @@ static bool qobject_output_type_null(Visitor *v, const char *name,
     return true;
 }
 
-static bool qobject_output_deprecated(Visitor *v, const char *name)
+static bool qobject_output_policy_skip(Visitor *v, const char *name,
+                                       unsigned special_features)
 {
-    return v->compat_policy.deprecated_output != COMPAT_POLICY_OUTPUT_HIDE;
+    CompatPolicy *pol = &v->compat_policy;
+
+    return ((special_features & 1u << QAPI_DEPRECATED)
+            && pol->deprecated_output == COMPAT_POLICY_OUTPUT_HIDE)
+        || ((special_features & 1u << QAPI_UNSTABLE)
+            && pol->unstable_output == COMPAT_POLICY_OUTPUT_HIDE);
 }
 
 /* Finish building, and return the root object.
@@ -262,7 +269,7 @@ 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.policy_skip = qobject_output_policy_skip;
     v->visitor.complete = qobject_output_complete;
     v->visitor.free = qobject_output_free;
 
diff --git a/qapi/qom.json b/qapi/qom.json
index 7231ac3f34..ccd1167808 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -559,10 +559,8 @@
 #                                        for ramblock-id. Disable this for 4.0
 #                                        machine types or older to allow
 #                                        migration with newer QEMU versions.
-#                                        This option is considered stable
-#                                        despite the x- prefix. (default:
-#                                        false generally, but true for machine
-#                                        types <= 4.0)
+#                                        (default: false generally,
+#                                        but true for machine types <= 4.0)
 #
 # Note: prealloc=true and reserve=false cannot be set at the same time. With
 #       reserve=true, the behavior depends on the operating system: for example,
@@ -785,6 +783,9 @@
 ##
 # @ObjectType:
 #
+# Features:
+# @unstable: Member @x-remote-object is experimental.
+#
 # Since: 6.0
 ##
 { 'enum': 'ObjectType',
@@ -836,7 +837,7 @@
     'tls-creds-psk',
     'tls-creds-x509',
     'tls-cipher-suites',
-    'x-remote-object'
+    { 'name': 'x-remote-object', 'features': [ 'unstable' ] }
   ] }
 
 ##
diff --git a/qapi/trace-events b/qapi/trace-events
index cccafc07e5..ab108c4f0e 100644
--- a/qapi/trace-events
+++ b/qapi/trace-events
@@ -17,8 +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_policy_reject(void *v, const char *name) "v=%p name=%s"
+visit_policy_skip(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 5f375bbfa6..f051536b63 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3641,7 +3641,9 @@ 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",
+    "                Policy for handling deprecated management interfaces\n"
+    "-compat [unstable-input=accept|reject|crash][,unstable-output=accept|hide]\n"
+    "                Policy for handling unstable management interfaces\n",
     QEMU_ARCH_ALL)
 SRST
 ``-compat [deprecated-input=@var{input-policy}][,deprecated-output=@var{output-policy}]``
@@ -3659,6 +3661,22 @@ SRST
         Suppress deprecated command results and events
 
     Limitation: covers only syntactic aspects of QMP.
+
+``-compat [unstable-input=@var{input-policy}][,unstable-output=@var{output-policy}]``
+    Set policy for handling unstable management interfaces (experimental):
+
+    ``unstable-input=accept`` (default)
+        Accept unstable commands and arguments
+    ``unstable-input=reject``
+        Reject unstable commands and arguments
+    ``unstable-input=crash``
+        Crash on unstable commands and arguments
+    ``unstable-output=accept`` (default)
+        Emit unstable command results and events
+    ``unstable-output=hide``
+        Suppress unstable command results and events
+
+    Limitation: covers only syntactic aspects of QMP.
 ERST
 
 DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index 3654825968..21001bbd6b 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -26,6 +26,7 @@ from .gen import (
     QAPISchemaModularCVisitor,
     build_params,
     ifcontext,
+    gen_special_features,
 )
 from .schema import (
     QAPISchema,
@@ -217,9 +218,6 @@ def gen_register_command(name: str,
                          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:
@@ -229,15 +227,13 @@ def gen_register_command(name: str,
     if coroutine:
         options += ['QCO_COROUTINE']
 
-    if not options:
-        options = ['QCO_NO_OPTIONS']
-
     ret = mcgen('''
     qmp_register_command(cmds, "%(name)s",
-                         qmp_marshal_%(c_name)s, %(opts)s);
+                         qmp_marshal_%(c_name)s, %(opts)s, %(feats)s);
 ''',
                 name=name, c_name=c_name(name),
-                opts=" | ".join(options))
+                opts=' | '.join(options) or 0,
+                feats=gen_special_features(features))
     return ret
 
 
diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
index 82475e84ec..27b44c49f5 100644
--- a/scripts/qapi/events.py
+++ b/scripts/qapi/events.py
@@ -109,13 +109,15 @@ 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('''
+    for f in features:
+        if f.is_special():
+            ret += mcgen('''
 
-    if (compat_policy.deprecated_output == COMPAT_POLICY_OUTPUT_HIDE) {
+    if (compat_policy.%(feat)s_output == COMPAT_POLICY_OUTPUT_HIDE) {
         return;
     }
-''')
+''',
+                         feat=f.name)
 
     ret += mcgen('''
 
diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py
index 2ec1e7b3b6..995a97d2b8 100644
--- a/scripts/qapi/gen.py
+++ b/scripts/qapi/gen.py
@@ -18,6 +18,7 @@ from typing import (
     Dict,
     Iterator,
     Optional,
+    Sequence,
     Tuple,
 )
 
@@ -29,6 +30,7 @@ from .common import (
     mcgen,
 )
 from .schema import (
+    QAPISchemaFeature,
     QAPISchemaIfCond,
     QAPISchemaModule,
     QAPISchemaObjectType,
@@ -37,6 +39,12 @@ from .schema import (
 from .source import QAPISourceInfo
 
 
+def gen_special_features(features: Sequence[QAPISchemaFeature]) -> str:
+    special_features = [f"1u << QAPI_{feat.name.upper()}"
+                        for feat in features if feat.is_special()]
+    return ' | '.join(special_features) or '0'
+
+
 class QAPIGen:
     def __init__(self, fname: str):
         self.fname = fname
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 6d5f46509a..b7b3fc0ce4 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -254,9 +254,11 @@ class QAPISchemaType(QAPISchemaEntity):
 
     def check(self, schema):
         QAPISchemaEntity.check(self, schema)
-        if 'deprecated' in [f.name for f in self.features]:
-            raise QAPISemError(
-                self.info, "feature 'deprecated' is not supported for types")
+        for feat in self.features:
+            if feat.is_special():
+                raise QAPISemError(
+                    self.info,
+                    f"feature '{feat.name}' is not supported for types")
 
     def describe(self):
         assert self.meta
@@ -725,6 +727,9 @@ class QAPISchemaEnumMember(QAPISchemaMember):
 class QAPISchemaFeature(QAPISchemaMember):
     role = 'feature'
 
+    def is_special(self):
+        return self.name in ('deprecated', 'unstable')
+
 
 class QAPISchemaObjectTypeMember(QAPISchemaMember):
     def __init__(self, name, info, typ, optional, ifcond=None, features=None):
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
index ab2441adc9..3013329c24 100644
--- a/scripts/qapi/types.py
+++ b/scripts/qapi/types.py
@@ -16,7 +16,7 @@ This work is licensed under the terms of the GNU GPL, version 2.
 from typing import List, Optional
 
 from .common import c_enum_const, c_name, mcgen
-from .gen import QAPISchemaModularCVisitor, ifcontext
+from .gen import QAPISchemaModularCVisitor, gen_special_features, ifcontext
 from .schema import (
     QAPISchema,
     QAPISchemaEnumMember,
@@ -39,7 +39,7 @@ def gen_enum_lookup(name: str,
                     members: List[QAPISchemaEnumMember],
                     prefix: Optional[str] = None) -> str:
     max_index = c_enum_const(name, '_MAX', prefix)
-    flags = ''
+    feats = ''
     ret = mcgen('''
 
 const QEnumLookup %(c_name)s_lookup = {
@@ -54,19 +54,21 @@ const QEnumLookup %(c_name)s_lookup = {
 ''',
                      index=index, name=memb.name)
         ret += memb.ifcond.gen_endif()
-        if 'deprecated' in (f.name for f in memb.features):
-            flags += mcgen('''
-        [%(index)s] = QAPI_ENUM_DEPRECATED,
+
+        special_features = gen_special_features(memb.features)
+        if special_features != '0':
+            feats += mcgen('''
+        [%(index)s] = %(special_features)s,
 ''',
-                           index=index)
+                           index=index, special_features=special_features)
 
-    if flags:
+    if feats:
         ret += mcgen('''
     },
-    .flags = (const unsigned char[%(max_index)s]) {
+    .special_features = (const unsigned char[%(max_index)s]) {
 ''',
                      max_index=max_index)
-        ret += flags
+        ret += feats
 
     ret += mcgen('''
     },
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 9d9196a143..e13bbe4292 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -21,7 +21,7 @@ from .common import (
     indent,
     mcgen,
 )
-from .gen import QAPISchemaModularCVisitor, ifcontext
+from .gen import QAPISchemaModularCVisitor, gen_special_features, ifcontext
 from .schema import (
     QAPISchema,
     QAPISchemaEnumMember,
@@ -76,7 +76,6 @@ 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 += memb.ifcond.gen_if()
         if memb.optional:
             ret += mcgen('''
@@ -84,14 +83,15 @@ 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:
+        special_features = gen_special_features(memb.features)
+        if special_features != '0':
             ret += mcgen('''
-    if (!visit_deprecated_accept(v, "%(name)s", errp)) {
+    if (visit_policy_reject(v, "%(name)s", %(special_features)s, errp)) {
         return false;
     }
-    if (visit_deprecated(v, "%(name)s")) {
+    if (!visit_policy_skip(v, "%(name)s", %(special_features)s)) {
 ''',
-                         name=memb.name)
+                         name=memb.name, special_features=special_features)
             indent.increase()
         ret += mcgen('''
     if (!visit_type_%(c_type)s(v, "%(name)s", &obj->%(c_name)s, errp)) {
@@ -100,7 +100,7 @@ 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:
+        if special_features != '0':
             indent.decrease()
             ret += mcgen('''
     }
diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
index 10a1a33761..52cf17e8ac 100644
--- a/storage-daemon/qemu-storage-daemon.c
+++ b/storage-daemon/qemu-storage-daemon.c
@@ -146,7 +146,8 @@ static void init_qmp_commands(void)
 
     QTAILQ_INIT(&qmp_cap_negotiation_commands);
     qmp_register_command(&qmp_cap_negotiation_commands, "qmp_capabilities",
-                         qmp_marshal_qmp_capabilities, QCO_ALLOW_PRECONFIG);
+                         qmp_marshal_qmp_capabilities,
+                         QCO_ALLOW_PRECONFIG, 0);
 }
 
 static int getopt_set_loc(int argc, char **argv, const char *optstring,
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index b677ab861d..43b8697002 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -273,7 +273,7 @@
   'data': { 'foo': { 'type': 'int', 'features': [ 'deprecated' ] } },
   'features': [ 'feature1' ] }
 { 'struct': 'FeatureStruct2',
-  'data': { 'foo': 'int' },
+  'data': { 'foo': { 'type': 'int', 'features': [ 'unstable' ] } },
   'features': [ { 'name': 'feature1' } ] }
 { 'struct': 'FeatureStruct3',
   'data': { 'foo': 'int' },
@@ -331,7 +331,7 @@
 { 'command': 'test-command-features1',
   'features': [ 'deprecated' ] }
 { 'command': 'test-command-features3',
-  'features': [ 'feature1', 'feature2' ] }
+  'features': [ 'unstable', 'feature1', 'feature2' ] }
 
 { 'command': 'test-command-cond-features1',
   'features': [ { 'name': 'feature1', 'if': 'TEST_IF_FEATURE_1'} ] }
@@ -348,3 +348,6 @@
 
 { 'event': 'TEST_EVENT_FEATURES1',
   'features': [ 'deprecated' ] }
+
+{ 'event': 'TEST_EVENT_FEATURES2',
+  'features': [ 'unstable' ] }
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index 16846dbeb8..1f9585fa9b 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -308,6 +308,7 @@ object FeatureStruct1
     feature feature1
 object FeatureStruct2
     member foo: int optional=False
+        feature unstable
     feature feature1
 object FeatureStruct3
     member foo: int optional=False
@@ -373,6 +374,7 @@ command test-command-features1 None -> None
     feature deprecated
 command test-command-features3 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
+    feature unstable
     feature feature1
     feature feature2
 command test-command-cond-features1 None -> None
@@ -394,6 +396,9 @@ event TEST_EVENT_FEATURES0 FeatureStruct1
 event TEST_EVENT_FEATURES1 None
     boxed=False
     feature deprecated
+event TEST_EVENT_FEATURES2 None
+    boxed=False
+    feature unstable
 module include/sub-module.json
 include sub-sub-module.json
 object SecondArrayRef