Re: [PATCH v2 10/10] migration: Switch to TYPE_OBJECT with object properties

[Fabiano Rosas <farosas@suse.de>]

Peter Xu <peterx@redhat.com> writes:

> On Wed, Jun 10, 2026 at 05:13:47PM +0100, Daniel P. Berrangé wrote:
>> On Tue, Jun 09, 2026 at 01:25:14PM -0400, Peter Xu wrote:
>> > The migration object used to depend on TYPE_DEVICE due to:
>> > 
>> > - Usage of qdev properties
>> > - Apply compat properties and global properties
>> > 
>> > This patch re-based the object to TYPE_OBJECT with the changes:
>> > 
>> > - Switch to object properties API
>> > - Manually apply both compat and global properties in post_init()
>> > 
>> > Note that to avoid too many property getter/setter helpers, this patch used
>> > the object_property_add_*_ptr_def() APIs so that an pointer is passed to
>> > bind to the property.  Such API is used for most of the conversions.
>> > 
>> > After patch, the migration object initializes instance properties within
>> > its instance_init() callback, in migrate_params_init().
>> > 
>> > One side effect of this change is, since we switched to a loop to add all
>> > capabilities, the name of the properties representing a migration
>> > capability may chance from previously hard-coded ones (many with x-).  It's
>> > fine since it's only used in -global so it's only for debugging.
>> > 
>> > Similarly, I removed "x-" from other properites that used to start with
>> > "x-" but actually are not experimental.
>> 
>> Mixing such a change into a refactoring commit is bad practice,
>> can you keep property changes separated.
>
> Sure.
>
>> 
>> > After the whole conversion, we don't need migration_properties or the count
>> > anymore, hence can be removed.  While at it, we can also remove two
>> > DEFINE_PROP*() API that only migration uses (DEFINE_PROP_STR_OR_NULL, and
>> > DEFINE_PROP_MIG_CAP).
>> > 
>> > Signed-off-by: Peter Xu <peterx@redhat.com>
>> > ---
>> >  migration/options.h   |   8 +-
>> >  migration/migration.c |  35 ++-
>> >  migration/options.c   | 526 ++++++++++++++++++++++++++----------------
>> >  3 files changed, 351 insertions(+), 218 deletions(-)
>> 
>> 
>> > diff --git a/migration/options.c b/migration/options.c
>> > index 5cbfd29099..1cc99382d3 100644
>> > --- a/migration/options.c
>> > +++ b/migration/options.c
>> > @@ -54,7 +54,7 @@
>> 
>> 
>> > +static void migration_object_init_props_bool(MigrationState *s)
>> >  {
>> > -    const Property *prop = opaque;
>> > -    StrOrNull **ptr = object_field_prop_ptr(obj, prop);
>> > -    StrOrNull *str_or_null = *ptr;
>> > +    Object *obj = OBJECT(s);
>> > +    int i;
>> >  
>> > -    /*
>> > -     * The property should never be NULL because it's part of
>> > -     * s->parameters and a default value is always set by qdev. It
>> > -     * should also never be QNULL as the setter doesn't allow it.
>> > -     */
>> > -    assert(str_or_null && str_or_null->type != QTYPE_QNULL);
>> > -    visit_type_str(v, name, &str_or_null->u.s, errp);
>> > +    struct MigPropBool {
>> > +        const char *name;
>> > +        void *ptr;
>> > +        bool defvar;
>> > +    } bool_list[] = {
>> > +        {
>> > +            "store-global-state",
>> > +            &s->store_global_state,
>> > +            true,
>> > +        },
>> > +        {
>> > +            "send-configuration",
>> > +            &s->send_configuration,
>> > +            true,
>> > +        },
>> > +        {
>> > +            "send-section-footer",
>> > +            &s->send_section_footer,
>> > +            true,
>> > +        },
>> > +        {
>> > +            "send-switchover-start",
>> > +            &s->send_switchover_start,
>> > +            true,
>> > +        },
>> > +        {
>> > +            "x-preempt-pre-7-2",
>> > +            &s->preempt_pre_7_2,
>> > +            false,
>> > +        },
>> > +        {
>> > +            "x-cpu-throttle-tailslow",
>> > +            &s->parameters.cpu_throttle_tailslow,
>> > +            false,
>> > +        },
>> > +        {
>> > +            "multifd-clean-tls-termination",
>> > +            &s->multifd_clean_tls_termination,
>> > +            true,
>> > +        },
>> > +        {
>> > +            "multifd-flush-after-each-section",
>> > +            &s->multifd_flush_after_each_section,
>> > +            false,
>> > +        },
>> > +    };
>> > +    struct MigPropBool *prop;
>> 
>> This approach to declaring properties is pretty unpleasant
>> to follow IMHO. Being a custom different approach from every
>> other object impl is not a good thing.
>
> [I asked this question elsewhere, I'll keep the discussion there]
>
>> 
>> > +
>> > +    for (i = 0; i < ARRAY_SIZE(bool_list); i++) {
>> > +        prop = &bool_list[i];
>> > +        object_property_add_bool_ptr_def(obj, prop->name,
>> > +                                         prop->ptr, prop->defvar);
>> > +    }
>> 
>> Using instance level properties is the old way to do things,
>> it is preferred to use class level properties instead.
>> 
>> This means you can't use the "ptr" concept to directly reference
>> the instance fields and have to provide setters / getters explicitly
>> instead, but as you've shown with the TLS properties,  a macro can
>> make it simple to define the repetitive getters/setters.
>
> If pointer is unwanted, I can switch to some more macro magic.  But since
> this series got rewrote the 3rd time..  I'll make sure it's extremely
> required before doing it..
>
>> > +static void migration_object_init_props_enum(MigrationState *s)
>> > +{
>> > +    Object *obj = OBJECT(s);
>> > +    ObjectProperty *prop;
>> > +
>> > +    prop = object_property_add_enum(obj, "multifd-compression",
>> > +                                    "MultiFDCompression",
>> > +                                    &MultiFDCompression_lookup,
>> > +                                    mig_prop_multifd_compression_get,
>> > +                                    mig_prop_multifd_compression_set);
>> > +    object_property_set_default_str(prop, DEFAULT_MIGRATE_MULTIFD_COMPRESSION);
>> > +
>> > +    prop = object_property_add_enum(obj, "mode", "MigMode", &MigMode_lookup,
>> > +                                    mig_prop_mode_get, mig_prop_mode_set);
>> > +    object_property_set_default_str(prop, "normal");
>> > +
>> > +    prop = object_property_add_enum(obj, "zero-page-detection",
>> > +                                    "ZeroPageDetection",
>> > +                                    &ZeroPageDetection_lookup,
>> > +                                    mig_prop_zero_page_detection_get,
>> > +                                    mig_prop_zero_page_detection_set);
>> > +    object_property_set_default_str(prop, "multifd");
>> > +}
>> 
>> Perhaps I'm missing something, but I'm not seeing the point in
>> using the set_default methods - in fact I'm not really sure why
>> they exist in QOM at all.
>> 
>> I'd expect all defaults to be set in the instance _init method.
>> ie why isn't this done as:
>> 
>>    void migrate_params_init(MigrationState *s)
>>    {
>>       s->parameters.mode = MIG_MODE_NORMAL;
>>       s->parameters.zero_page_detection = ZERO_PAGE_DETECTION_MULTIFD;
>>       .... all other defaults...
>>    }
>
> Yes frankly I asked myself the same question when looking at this.
>
> I still saw quite some defvar references, type_print_class_properties() can
> be one example where we dump help message with default values but without
> the need to apply.  I didn't check the rest.  If the concept exists and if
> we will be using qobj props, IMHO sticking with it is defintely safer so
> that all qom future defvar changes will apply and it'll just work there.
>
>> 
>> 
>> > +
>> > +static void migration_object_init_properties(MigrationState *s)
>> > +{
>> > +    migration_object_init_props_bool(s);
>> > +    migration_object_init_props_uint8(s);
>> > +    migration_object_init_props_uint32(s);
>> > +    migration_object_init_props_uint64(s);
>> > +    migration_object_init_props_size(s);
>> > +    migration_object_init_props_caps(s);
>> > +    migration_object_init_props_tls(s);
>> > +    migration_object_init_props_enum(s);
>> > +}
>> 
>> ...and class properties be registered in migrate_params_class_init()
>> and the grouping per type isn't helpful IMHO, just put all the
>> object_class_property_add calls inline in one place.
>
> I still want to avoid long functions, one way or another.
>
> Hopefully it makes sense when I have those arrays to init different type of
> props it makes sense to split with this, but I'm open to other way to
> split.  I still want to not make it a extremely long function.
>

I see why you did it that way, it's mostly a limitation of the object
code in that it requires the type of the default value only to convert
it to a QObject internally. IMO, this is backwards, the object.c code
should take the QObject and let the caller do the conversion.

I rewrote this part of the code using a ObjectProperties object as
intermediary, instead of MigProp*. I think this looks easier to parse,
although it's longer.

-->8--
From a6529d119d25ecc00f92686e2cddf1d81dc43183 Mon Sep 17 00:00:00 2001
From: Fabiano Rosas <farosas@suse.de>
Date: Wed, 10 Jun 2026 16:49:52 -0300
Subject: [PATCH] poc

---
 migration/options.c | 114 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)

diff --git a/migration/options.c b/migration/options.c
index 5a74aef0ad..7ab1079284 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -90,6 +90,120 @@
 #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT            1       /* MB/s */
 #define DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE           MiB
 
+#define defstr(def) QOBJECT(qstring_from_str((const char *)def))
+#define defbool(def) QOBJECT(qbool_from_bool((bool)def))
+#define defint(def) QOBJECT(qnum_from_int((int64_t)def))
+#define defuint(def) QOBJECT(qnum_from_uint(def))
+
+#define defuint8 defuint
+#define defuint16 defuint
+#define defuint32 defuint
+#define defuint64 defuint
+#define defenum defstr
+#define defStrOrNull defstr
+#define defMigMode defenum
+#define defMultiFDCompression defenum
+#define defZeroPageDetection defenum
+
+#define DEFPROP_PTR_ACCESSOR(_t)                                        \
+    static void property_visit_type_##_t(Object *obj, Visitor *v,       \
+                                         const char *name, void *opaque, \
+                                         Error **errp)                  \
+    {                                                                   \
+        visit_type_##_t(v, name, opaque, errp);                         \
+    }                                                                   \
+                                                                        \
+    static inline ObjectProperty prop_##_t(const char *name, void *opaque, \
+                                           uint64_t def)                \
+    {                                                                   \
+        return (ObjectProperty) {                                       \
+            .name = (char *)name,                                       \
+            .type = (char *)"##_t",                                     \
+            .opaque = opaque,                                           \
+            .get = property_visit_type_##_t,                            \
+            .set = property_visit_type_##_t,                            \
+            .defval = def##_t(def),                                     \
+        };                                                              \
+    }                                                                   \
+
+DEFPROP_PTR_ACCESSOR(str);
+DEFPROP_PTR_ACCESSOR(bool);
+DEFPROP_PTR_ACCESSOR(int);
+DEFPROP_PTR_ACCESSOR(uint8);
+DEFPROP_PTR_ACCESSOR(uint16);
+DEFPROP_PTR_ACCESSOR(uint32);
+DEFPROP_PTR_ACCESSOR(uint64);
+DEFPROP_PTR_ACCESSOR(StrOrNull);
+DEFPROP_PTR_ACCESSOR(MigMode);
+DEFPROP_PTR_ACCESSOR(MultiFDCompression);
+DEFPROP_PTR_ACCESSOR(ZeroPageDetection);
+
+static void migration_object_init_properties(MigrationState *s)
+{
+    Object *obj = OBJECT(s);
+    ObjectProperty props_list[] = {
+        prop_bool("store-global-state", &s->store_global_state, true),
+        prop_bool("send-configuration", &s->send_configuration, true),
+        prop_bool("send-section-footer", &s->send_section_footer, true),
+        prop_bool("send-switchover-start", &s->send_switchover_start, true),
+        prop_bool("x-preempt-pre-7-2", &s->preempt_pre_7_2, false),
+        prop_bool("x-cpu-throttle-tailslow", &s->parameters.cpu_throttle_tailslow, false),
+        prop_bool("multifd-clean-tls-termination", &s->multifd_clean_tls_termination, true),
+        prop_bool("multifd-flush-after-each-section", &s->multifd_flush_after_each_section, false),
+
+        prop_uint8("clear-bitmap-shift", &s->clear_bitmap_shift, CLEAR_BITMAP_SHIFT_DEFAULT),
+        prop_uint8("throttle-trigger-threshold", &s->parameters.throttle_trigger_threshold, DEFAULT_MIGRATE_THROTTLE_TRIGGER_THRESHOLD),
+        prop_uint8("cpu-throttle-initial", &s->parameters.cpu_throttle_initial, DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL),
+        prop_uint8("cpu-throttle-increment", &s->parameters.cpu_throttle_increment, DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT),
+        prop_uint8("multifd-channels", &s->parameters.multifd_channels, DEFAULT_MIGRATE_MULTIFD_CHANNELS),
+        prop_uint8("multifd-zlib-level", &s->parameters.multifd_zlib_level, DEFAULT_MIGRATE_MULTIFD_ZLIB_LEVEL),
+        prop_uint8("multifd-qatzip-level", &s->parameters.multifd_qatzip_level, DEFAULT_MIGRATE_MULTIFD_QATZIP_LEVEL),
+        prop_uint8("multifd-zstd-level", &s->parameters.multifd_zstd_level, DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL),
+        prop_uint8("max-cpu-throttle", &s->parameters.max_cpu_throttle, DEFAULT_MIGRATE_MAX_CPU_THROTTLE),
+
+        prop_uint32("x-checkpoint-delay", &s->parameters.x_checkpoint_delay, DEFAULT_MIGRATE_X_CHECKPOINT_DELAY),
+
+        prop_uint64("downtime-limit", &s->parameters.downtime_limit, DEFAULT_MIGRATE_SET_DOWNTIME),
+        prop_uint64("x-vcpu-dirty-limit-period", &s->parameters.x_vcpu_dirty_limit_period, DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT_PERIOD),
+        prop_uint64("vcpu-dirty-limit", &s->parameters.vcpu_dirty_limit, DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT),
+        prop_uint64("x-rdma-chunk-size", &s->parameters.x_rdma_chunk_size, DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE),
+        prop_uint64("xbzrle-cache-size", &s->parameters.xbzrle_cache_size, DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
+        prop_uint64("max-postcopy-bandwidth", &s->parameters.max_postcopy_bandwidth, DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH),
+        prop_uint64("announce-initial", &s->parameters.announce_initial, DEFAULT_MIGRATE_ANNOUNCE_INITIAL),
+        prop_uint64("announce-max", &s->parameters.announce_max, DEFAULT_MIGRATE_ANNOUNCE_MAX),
+        prop_uint64("announce-rounds", &s->parameters.announce_rounds, DEFAULT_MIGRATE_ANNOUNCE_ROUNDS),
+        prop_uint64("announce-step", &s->parameters.announce_step, DEFAULT_MIGRATE_ANNOUNCE_STEP),
+        prop_uint64("max-bandwidth", &s->parameters.max_bandwidth, MAX_THROTTLE),
+        prop_uint64("avail-switchover-bandwidth", &s->parameters.avail_switchover_bandwidth, 0),
+
+        prop_StrOrNull("tls-creds", &s->parameters.tls_creds, (uint64_t)""),
+        prop_StrOrNull("tls-hostname", &s->parameters.tls_hostname, (uint64_t)""),
+        prop_StrOrNull("tls-authz", &s->parameters.tls_authz, (uint64_t)""),
+
+        prop_MigMode("mode", &s->parameters.mode, (uint64_t)"normal"),
+        prop_MultiFDCompression("multifd-compression", &s->parameters.multifd_compression, (uint64_t)DEFAULT_MIGRATE_MULTIFD_COMPRESSION),
+        prop_ZeroPageDetection("zero-page-detection", &s->parameters.zero_page_detection, (uint64_t)"multifd"),
+    };
+
+    for (int i = 0; i < ARRAY_SIZE(props_list); i++) {
+        ObjectProperty *new;
+        ObjectProperty *in = &props_list[i];
+
+        new = object_property_add(obj, in->name, in->type, in->get, in->set,
+                                  in->release, in->opaque);
+        object_property_set_default(new, in->defval);
+    }
+
+    /* Migration capabilities are always turned off by default */
+    for (int i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
+        ObjectProperty prop, *new;
+
+        prop = prop_bool(MigrationCapability_str(i), &s->capabilities[i], false);
+        new = object_property_add(obj, prop.name, prop.type, prop.get, prop.set,
+                                  NULL, prop.opaque);
+        object_property_set_default(new, prop.defval);
+    }
+}
 
 bool migrate_auto_converge(void)
 {
-- 
2.53.0