qom: replace 'can_be_deleted' with 'prepare_delete'
While most objects can perform all their cleanup in the finalizer method, there can be interactions with other resources / subsystems / threads which require that some cleanup be performed on an user creatable object before unparenting it and entering finalization. The current 'can_be_deleted' method runs in the deletion path and is intended to be used to block deletion. While it could be used to perform cleanup tasks, its name suggests it should be free of side-effects. Generalize this by renaming it to 'prepare_delete', explicitly allowing for cleanup to be provided. Existing users of 'can_be_deleted' are re-written, which provides them with more detailed/tailored error messages. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> Message-ID: <20260706135824.2623960-2-berrange@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
Daniel P. Berrangé committed
Jul 6, 2026 at 14:57 UTC
9c3b2c9db50b7110db7fe294903946a07675ff3b
11 files changed
+68
-39
backends/cryptodev.c
+9
-3
@@ -454,9 +454,15 @@ bool cryptodev_backend_is_ready(CryptoDevBackend *backend)
454
}
455
456
static bool
457
-cryptodev_backend_can_be_deleted(UserCreatable *uc)
457
+cryptodev_backend_prepare_delete(UserCreatable *uc, Error **errp)
458
{
459
- return !cryptodev_backend_is_used(CRYPTODEV_BACKEND(uc));
459
+ if (cryptodev_backend_is_used(CRYPTODEV_BACKEND(uc))) {
460
+ error_setg(errp,
461
+ "Cannot delete cryptodev backend '%s' that is in use",
462
+ object_get_canonical_path_component(OBJECT(uc)));
463
+ return false;
464
+ }
465
+ return true;
466
}
467
468
static void cryptodev_backend_instance_init(Object *obj)
@@ -613,7 +619,7 @@ cryptodev_backend_class_init(ObjectClass *oc, const void *data)
619
UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
620
621
ucc->complete = cryptodev_backend_complete;
616
- ucc->can_be_deleted = cryptodev_backend_can_be_deleted;
622
+ ucc->prepare_delete = cryptodev_backend_prepare_delete;
623
624
QTAILQ_INIT(&crypto_clients);
625
object_class_property_add(oc, "queues", "uint32",
backends/hostmem.c
+5
-2
@@ -434,9 +434,12 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
434
}
435
436
static bool
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-host_memory_backend_can_be_deleted(UserCreatable *uc)
437
+host_memory_backend_prepare_delete(UserCreatable *uc, Error **errp)
438
{
439
if (host_memory_backend_is_mapped(MEMORY_BACKEND(uc))) {
440
+ error_setg(errp,
441
+ "Cannot delete host memory backend '%s' which is mapped",
442
+ object_get_canonical_path_component(OBJECT(uc)));
443
return false;
444
} else {
445
return true;
@@ -508,7 +511,7 @@ host_memory_backend_class_init(ObjectClass *oc, const void *data)
511
UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
512
513
ucc->complete = host_memory_backend_memory_complete;
511
- ucc->can_be_deleted = host_memory_backend_can_be_deleted;
514
+ ucc->prepare_delete = host_memory_backend_prepare_delete;
515
516
object_class_property_add_bool(oc, "merge",
517
host_memory_backend_get_merge,
backends/iommufd.c
+8
-3
@@ -63,11 +63,16 @@ static void iommufd_backend_set_fd(Object *obj, const char *str, Error **errp)
63
trace_iommu_backend_set_fd(be->fd);
64
}
65
66
-static bool iommufd_backend_can_be_deleted(UserCreatable *uc)
66
+static bool iommufd_backend_prepare_delete(UserCreatable *uc, Error **errp)
67
{
68
IOMMUFDBackend *be = IOMMUFD_BACKEND(uc);
69
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- return !be->users;
70
+ if (be->users) {
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+ error_setg(errp, "Can not delete IOMMUFD backend '%s' with %d users",
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+ object_get_canonical_path_component(OBJECT(uc)), be->users);
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+ return false;
74
+ }
75
+ return true;
76
}
77
78
static void iommufd_backend_complete(UserCreatable *uc, Error **errp)
@@ -92,7 +97,7 @@ static void iommufd_backend_class_init(ObjectClass *oc, const void *data)
97
{
98
UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
99
95
- ucc->can_be_deleted = iommufd_backend_can_be_deleted;
100
+ ucc->prepare_delete = iommufd_backend_prepare_delete;
101
ucc->complete = iommufd_backend_complete;
102
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object_class_property_add_str(oc, "fd", NULL, iommufd_backend_set_fd);
block/throttle-groups.c
+9
-3
@@ -960,9 +960,15 @@ static void throttle_group_get_limits(Object *obj, Visitor *v,
960
visit_type_ThrottleLimits(v, name, &argp, errp);
961
}
962
963
-static bool throttle_group_can_be_deleted(UserCreatable *uc)
963
+static bool throttle_group_prepare_delete(UserCreatable *uc, Error **errp)
964
{
965
- return OBJECT(uc)->ref == 1;
965
+ if (OBJECT(uc)->ref > 1) {
966
+ error_setg(errp,
967
+ "Cannot delete throttle group '%s' with active references",
968
+ object_get_canonical_path_component(OBJECT(uc)));
969
+ return false;
970
+ }
971
+ return true;
972
}
973
974
static void throttle_group_obj_class_init(ObjectClass *klass,
@@ -972,7 +978,7 @@ static void throttle_group_obj_class_init(ObjectClass *klass,
978
UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
979
980
ucc->complete = throttle_group_obj_complete;
975
- ucc->can_be_deleted = throttle_group_can_be_deleted;
981
+ ucc->prepare_delete = throttle_group_prepare_delete;
982
983
/* individual properties */
984
for (i = 0; i < sizeof(properties) / sizeof(ThrottleParamInfo); i++) {
event-loop-base.c
+4
-4
@@ -85,13 +85,13 @@ static void event_loop_base_complete(UserCreatable *uc, Error **errp)
85
}
86
}
87
88
-static bool event_loop_base_can_be_deleted(UserCreatable *uc)
88
+static bool event_loop_base_prepare_delete(UserCreatable *uc, Error **errp)
89
{
90
EventLoopBaseClass *bc = EVENT_LOOP_BASE_GET_CLASS(uc);
91
EventLoopBase *backend = EVENT_LOOP_BASE(uc);
92
93
- if (bc->can_be_deleted) {
94
- return bc->can_be_deleted(backend);
93
+ if (bc->prepare_delete) {
94
+ return bc->prepare_delete(backend, errp);
95
}
96
97
return true;
@@ -102,7 +102,7 @@ static void event_loop_base_class_init(ObjectClass *klass,
102
{
103
UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
104
ucc->complete = event_loop_base_complete;
105
- ucc->can_be_deleted = event_loop_base_can_be_deleted;
105
+ ucc->prepare_delete = event_loop_base_prepare_delete;
106
107
object_class_property_add(klass, "aio-max-batch", "int",
108
event_loop_base_get_param,
include/qom/object_interfaces.h
+17
-9
@@ -20,8 +20,10 @@ typedef struct UserCreatable UserCreatable;
20
* UserCreatableClass:
21
* @parent_class: the base class
22
* @complete: callback to be called after @obj's properties are set.
23
- * @can_be_deleted: callback to be called before an object is removed
24
- * to check if @obj can be removed safely.
23
+ * @prepare_delete: to be called before an attempt to delete @obj
24
+ * to validate whether the object can be deleted and trigger any
25
+ * cleanup of any resources which have to be dealt with before the
26
+ * object is unparented and enters finalization.
27
*
28
* Interface is designed to work with -object/object-add/object_add
29
* commands.
@@ -36,7 +38,9 @@ typedef struct UserCreatable UserCreatable;
38
* For objects created without using -object/object-add/object_add,
39
* @user_creatable_complete() wrapper should be called manually if
40
* object's type implements USER_CREATABLE interface and needs
39
- * complete() callback to be called.
41
+ * complete() callback to be called. Similarly @user_creatable_prepare_delete()
42
+ * should be called manually prior to an attempt to the delete the
43
+ * object.
44
*/
45
struct UserCreatableClass {
46
/* <private> */
@@ -44,7 +48,7 @@ struct UserCreatableClass {
48
49
/* <public> */
50
void (*complete)(UserCreatable *uc, Error **errp);
47
- bool (*can_be_deleted)(UserCreatable *uc);
51
+ bool (*prepare_delete)(UserCreatable *uc, Error **errp);
52
};
53
54
/**
@@ -61,13 +65,17 @@ struct UserCreatableClass {
65
bool user_creatable_complete(UserCreatable *uc, Error **errp);
66
67
/**
64
- * user_creatable_can_be_deleted:
65
- * @uc: the object whose can_be_deleted() method is called if implemented
68
+ * user_creatable_prepare_delete:
69
+ * @uc: the user-creatable object whose prepare_delete() method is called
70
+ * @errp: if an error occurs, a pointer to an area to store the error
71
+ *
72
+ * Wrapper to call prepare_delete() class method if defined, otherwise
73
+ * does nothing.
74
*
67
- * Wrapper to call can_be_deleted() method if one of types it's inherited
68
- * from implements USER_CREATABLE interface.
75
+ * Returns: %true on success or if prepare_delete() is not defined,
76
+ * %false on failure.
77
*/
70
-bool user_creatable_can_be_deleted(UserCreatable *uc);
78
+bool user_creatable_prepare_delete(UserCreatable *uc, Error **errp);
79
80
/**
81
* user_creatable_add_qapi:
include/system/event-loop-base.h
+1
-1
@@ -24,7 +24,7 @@ struct EventLoopBaseClass {
24
25
void (*init)(EventLoopBase *base, Error **errp);
26
void (*update_params)(EventLoopBase *base, Error **errp);
27
- bool (*can_be_deleted)(EventLoopBase *base);
27
+ bool (*prepare_delete)(EventLoopBase *base, Error **errp);
28
};
29
30
struct EventLoopBase {
net/can/can_core.c
+4
-2
@@ -143,8 +143,10 @@ int can_bus_client_set_filters(CanBusClientState *client,
143
}
144
145
146
-static bool can_bus_can_be_deleted(UserCreatable *uc)
146
+static bool can_bus_prepare_delete(UserCreatable *uc, Error **errp)
147
{
148
+ error_setg(errp, "Deleting CAN bus device '%s' is not supported",
149
+ object_get_canonical_path_component(OBJECT(uc)));
150
return false;
151
}
152
@@ -153,7 +155,7 @@ static void can_bus_class_init(ObjectClass *klass,
155
{
156
UserCreatableClass *uc_klass = USER_CREATABLE_CLASS(klass);
157
156
- uc_klass->can_be_deleted = can_bus_can_be_deleted;
158
+ uc_klass->prepare_delete = can_bus_prepare_delete;
159
}
160
161
static const TypeInfo can_bus_info = {
qom/object_interfaces.c
+5
-8
@@ -32,16 +32,14 @@ bool user_creatable_complete(UserCreatable *uc, Error **errp)
32
return !*errp;
33
}
34
35
-bool user_creatable_can_be_deleted(UserCreatable *uc)
35
+bool user_creatable_prepare_delete(UserCreatable *uc, Error **errp)
36
{
37
-
37
UserCreatableClass *ucc = USER_CREATABLE_GET_CLASS(uc);
38
40
- if (ucc->can_be_deleted) {
41
- return ucc->can_be_deleted(uc);
42
- } else {
43
- return true;
39
+ if (ucc->prepare_delete) {
40
+ return ucc->prepare_delete(uc, errp);
41
}
42
+ return true;
43
}
44
45
void user_creatable_add_qapi(ObjectOptions *options, Error **errp)
@@ -253,8 +251,7 @@ bool user_creatable_del(const char *id, Error **errp)
251
return false;
252
}
253
256
- if (!user_creatable_can_be_deleted(USER_CREATABLE(obj))) {
257
- error_setg(errp, "object '%s' is in use, can not be deleted", id);
254
+ if (!user_creatable_prepare_delete(USER_CREATABLE(obj), errp)) {
255
return false;
256
}
257
tests/qemu-iotests/245
+2
-2
@@ -801,7 +801,7 @@ class TestBlockdevReopen(iotests.QMPTestCase):
801
# Now group1 is in use, it cannot be deleted
802
result = self.vm.qmp('object-del', id = 'group1')
803
self.assert_qmp(result, 'error/class', 'GenericError')
804
- self.assert_qmp(result, 'error/desc', "object 'group1' is in use, can not be deleted")
804
+ self.assert_qmp(result, 'error/desc', "Cannot delete throttle group 'group1' with active references")
805
806
# Default options, this switches the group back to group0
807
self.reopen(opts)
@@ -809,7 +809,7 @@ class TestBlockdevReopen(iotests.QMPTestCase):
809
# So now we cannot delete group0
810
result = self.vm.qmp('object-del', id = 'group0')
811
self.assert_qmp(result, 'error/class', 'GenericError')
812
- self.assert_qmp(result, 'error/desc', "object 'group0' is in use, can not be deleted")
812
+ self.assert_qmp(result, 'error/desc', "Cannot delete throttle group 'group0' with active references")
813
814
# But group1 is free this time, and it can be deleted
815
self.vm.cmd('object-del', id = 'group1')
util/main-loop.c
+4
-2
@@ -218,8 +218,10 @@ static void main_loop_init(EventLoopBase *base, Error **errp)
218
mloop = m;
219
}
220
221
-static bool main_loop_can_be_deleted(EventLoopBase *base)
221
+static bool main_loop_prepare_delete(EventLoopBase *base, Error **errp)
222
{
223
+ error_setg(errp, "Deleting main loop '%s' is not supported",
224
+ object_get_canonical_path_component(OBJECT(base)));
225
return false;
226
}
227
@@ -229,7 +231,7 @@ static void main_loop_class_init(ObjectClass *oc, const void *class_data)
231
232
bc->init = main_loop_init;
233
bc->update_params = main_loop_update_params;
232
- bc->can_be_deleted = main_loop_can_be_deleted;
234
+ bc->prepare_delete = main_loop_prepare_delete;
235
}
236
237
static const TypeInfo main_loop_info = {