migration: Add a qdev property for StrOrNull

The MigrationState is a QOM object with TYPE_DEVICE as a parent. This
was done about eight years ago so the migration code could make use of
qdev properties to define the defaults for the migration parameters
and to be able to expose migration knobs for debugging via the
'-global migration' command line option.

Due to unrelated historical reasons, three of the migration parameters
(TLS options) received different types when used via the
query-migrate-parameters QMP command than with the
migrate-set-parameters command. This has created a lot of duplication
in the migration code and in the QAPI documentation because the whole
of MigrationParameters had to be duplicated as well.

The migration code is now being fixed to remove the duplication and
for that to happen the offending fields need to be reconciled into a
single type. The StrOrNull type is going to be used.

To keep the command line compatibility, the parameters need to
continue being exposed via qdev properties accessible from the command
line. Introduce a qdev property StrOrNull just for that.

Note that this code is being kept in migration/options.c as this
version of StrOrNull doesn't need to handle QNULL because it was never
a valid option in the previous command line, which took a string.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Acked-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20251215220041.12657-4-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/migration/options.c b/migration/options.c
index ea19b2c7cdecd504878c48e5bd8d06f5ba6048de..d55f3104beac7ed34e3f2175bbf25c1d88047249 100644 (file)
--- a/migration/options.c
+++ b/migration/options.c
@@ -83,6 +83,11 @@
 #define DEFINE_PROP_MIG_CAP(name, x)             \
     DEFINE_PROP_BOOL(name, MigrationState, capabilities[x], false)
 
+const PropertyInfo qdev_prop_StrOrNull;
+#define DEFINE_PROP_STR_OR_NULL(_name, _state, _field)                  \
+    DEFINE_PROP(_name, _state, _field, qdev_prop_StrOrNull, StrOrNull *, \
+                .set_default = true)
+
 #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT_PERIOD     1000    /* milliseconds */
 #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT            1       /* MB/s */
 
@@ -208,6 +213,68 @@ const Property migration_properties[] = {
 };
 const size_t migration_properties_count = ARRAY_SIZE(migration_properties);
 
+static void get_StrOrNull(Object *obj, Visitor *v, const char *name,
+                          void *opaque, Error **errp)
+{
+    const Property *prop = opaque;
+    StrOrNull **ptr = object_field_prop_ptr(obj, prop);
+    StrOrNull *str_or_null = *ptr;
+
+    if (!str_or_null) {
+        str_or_null = g_new0(StrOrNull, 1);
+        str_or_null->type = QTYPE_QSTRING;
+        str_or_null->u.s = g_strdup("");
+    } else {
+        /* the setter doesn't allow QNULL */
+        assert(str_or_null->type != QTYPE_QNULL);
+    }
+    visit_type_str(v, name, &str_or_null->u.s, errp);
+}
+
+static void set_StrOrNull(Object *obj, Visitor *v, const char *name,
+                          void *opaque, Error **errp)
+{
+    const Property *prop = opaque;
+    StrOrNull **ptr = object_field_prop_ptr(obj, prop);
+    StrOrNull *str_or_null = g_new0(StrOrNull, 1);
+
+    /*
+     * Only str to keep compatibility, QNULL was never used via
+     * command line.
+     */
+    str_or_null->type = QTYPE_QSTRING;
+    if (!visit_type_str(v, name, &str_or_null->u.s, errp)) {
+        return;
+    }
+
+    qapi_free_StrOrNull(*ptr);
+    *ptr = str_or_null;
+}
+
+static void release_StrOrNull(Object *obj, const char *name, void *opaque)
+{
+    const Property *prop = opaque;
+    qapi_free_StrOrNull(*(StrOrNull **)object_field_prop_ptr(obj, prop));
+}
+
+static void set_default_value_tls_opt(ObjectProperty *op, const Property *prop)
+{
+    object_property_set_default_str(op, "");
+}
+
+/*
+ * String property like qdev_prop_string, except it's backed by a
+ * StrOrNull instead of a char *.  This is intended for
+ * TYPE_MIGRATION's TLS options.
+ */
+const PropertyInfo qdev_prop_StrOrNull = {
+    .type  = "StrOrNull",
+    .get = get_StrOrNull,
+    .set = set_StrOrNull,
+    .release = release_StrOrNull,
+    .set_default_value = set_default_value_tls_opt,
+};
+
 bool migrate_auto_converge(void)
 {
     MigrationState *s = migrate_get_current();