migration: Unshare MigrationParameters struct for now

Commit de63ab6 "migrate: Share common MigrationParameters struct"
reused MigrationParameters for the arguments of
migrate-set-parameters, with the following rationale:

    It is rather verbose, and slightly error-prone, to repeat
    the same set of parameters for input (migrate-set-parameters)
    as for output (query-migrate-parameters), where the only
    difference is whether the members are optional.  We can just
    document that the optional members will always be present
    on output, and then share a common struct between both
    commands.  The next patch can then reduce the amount of
    code needed on input.

I need to unshare them to correct a design flaw in a stupid, but
minimally invasive way, in the next commit.  We can restore the
sharing when we redo that patch in a less stupid way.  Add a suitable
TODO comment.

Note that I revert only the sharing part of commit de63ab6, not the
part that made the members of query-migrate-parameters' result
optional.  The schema (and thus introspection) remains inaccurate for
query-migrate-parameters.  If we decide not to restore the sharing, we
should revert that part, too.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

migration/migration.c

@@ -742,7 +742,59 @@ static bool migrate_params_check(MigrationParameters *params, Error **errp)
     return true;
 }
 
-static void migrate_params_apply(MigrationParameters *params)
+static void migrate_params_test_apply(MigrateSetParameters *params,
+                                      MigrationParameters *dest)
+{
+    *dest = migrate_get_current()->parameters;
+
+    /* TODO use QAPI_CLONE() instead of duplicating it inline */
+
+    if (params->has_compress_level) {
+        dest->compress_level = params->compress_level;
+    }
+
+    if (params->has_compress_threads) {
+        dest->compress_threads = params->compress_threads;
+    }
+
+    if (params->has_decompress_threads) {
+        dest->decompress_threads = params->decompress_threads;
+    }
+
+    if (params->has_cpu_throttle_initial) {
+        dest->cpu_throttle_initial = params->cpu_throttle_initial;
+    }
+
+    if (params->has_cpu_throttle_increment) {
+        dest->cpu_throttle_increment = params->cpu_throttle_increment;
+    }
+
+    if (params->has_tls_creds) {
+        dest->tls_creds = g_strdup(params->tls_creds);
+    }
+
+    if (params->has_tls_hostname) {
+        dest->tls_hostname = g_strdup(params->tls_hostname);
+    }
+
+    if (params->has_max_bandwidth) {
+        dest->max_bandwidth = params->max_bandwidth;
+    }
+
+    if (params->has_downtime_limit) {
+        dest->downtime_limit = params->downtime_limit;
+    }
+
+    if (params->has_x_checkpoint_delay) {
+        dest->x_checkpoint_delay = params->x_checkpoint_delay;
+    }
+
+    if (params->has_block_incremental) {
+        dest->block_incremental = params->block_incremental;
+    }
+}
+
+static void migrate_params_apply(MigrateSetParameters *params)
 {
     MigrationState *s = migrate_get_current();
 
@@ -802,9 +854,13 @@ static void migrate_params_apply(MigrationParameters *params)
     }
 }
 
-void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
+void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
 {
-    if (!migrate_params_check(params, errp)) {
+    MigrationParameters tmp;
+
+    migrate_params_test_apply(params, &tmp);
+
+    if (!migrate_params_check(&tmp, errp)) {
         /* Invalid parameter */
         return;
     }
@@ -1240,7 +1296,7 @@ int64_t qmp_query_migrate_cache_size(Error **errp)
 
 void qmp_migrate_set_speed(int64_t value, Error **errp)
 {
-    MigrationParameters p = {
+    MigrateSetParameters p = {
         .has_max_bandwidth = true,
         .max_bandwidth = value,
     };
@@ -1260,7 +1316,7 @@ void qmp_migrate_set_downtime(double value, Error **errp)
     value *= 1000; /* Convert to milliseconds */
     value = MAX(0, MIN(INT64_MAX, value));
 
-    MigrationParameters p = {
+    MigrateSetParameters p = {
         .has_downtime_limit = true,
         .downtime_limit = value,
     };