migration-test: Clean up string interpolation into QMP, part 2

Leaving interpolation into JSON to qmp() is more robust than building
QMP input manually, as explained in the recent commit "tests: Clean up
string interpolation into QMP input (simple cases)".

migrate() interpolates members into a JSON object.  Change it to take
its extra QMP arguments as arguments for qdict_from_jsonf_nofail()
instead of a string containing JSON members.

Bonus: gets rid of a non-literal format string.  A step towards
compile-time format string checking without triggering
-Wformat-nonliteral.

Cc: Juan Quintela <quintela@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <20180806065344.7103-20-armbru@redhat.com>

tests/migration-test.c

@@ -14,6 +14,7 @@
 
 #include "libqtest.h"
 #include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qjson.h"
 #include "qemu/option.h"
 #include "qemu/range.h"
 #include "qemu/sockets.h"
@@ -384,16 +385,25 @@ static void migrate_set_capability(QTestState *who, const char *capability,
     qobject_unref(rsp);
 }
 
-static void migrate(QTestState *who, const char *uri, const char *extra)
+/*
+ * Send QMP command "migrate".
+ * Arguments are built from @fmt... (formatted like
+ * qobject_from_jsonf_nofail()) with "uri": @uri spliced in.
+ */
+GCC_FMT_ATTR(3, 4)
+static void migrate(QTestState *who, const char *uri, const char *fmt, ...)
 {
-    QDict *rsp;
-    gchar *cmd;
+    va_list ap;
+    QDict *args, *rsp;
 
-    cmd = g_strdup_printf("{ 'execute': 'migrate',"
-                          "  'arguments': { 'uri': '%s' %s } }",
-                          uri, extra ? extra : "");
-    rsp = qtest_qmp(who, cmd);
-    g_free(cmd);
+    va_start(ap, fmt);
+    args = qdict_from_vjsonf_nofail(fmt, ap);
+    va_end(ap);
+
+    g_assert(!qdict_haskey(args, "uri"));
+    qdict_put_str(args, "uri", uri);
+
+    rsp = qmp("{ 'execute': 'migrate', 'arguments': %p}", args);
     g_assert(qdict_haskey(rsp, "return"));
     qobject_unref(rsp);
 }
@@ -585,7 +595,7 @@ static int migrate_postcopy_prepare(QTestState **from_ptr,
     /* Wait for the first serial output from the source */
     wait_for_serial("src_serial");
 
-    migrate(from, uri, NULL);
+    migrate(from, uri, "{}");
     g_free(uri);
 
     wait_for_migration_pass(from);
@@ -668,7 +678,7 @@ static void test_postcopy_recovery(void)
      * the newly created channel
      */
     wait_for_migration_status(from, "postcopy-paused");
-    migrate(from, uri, ", 'resume': true");
+    migrate(from, uri, "{'resume': true}");
     g_free(uri);
 
     /* Restore the postcopy bandwidth to unlimited */
@@ -687,7 +697,7 @@ static void test_baddest(void)
     if (test_migrate_start(&from, &to, "tcp:0:0", true)) {
         return;
     }
-    migrate(from, "tcp:0:0", NULL);
+    migrate(from, "tcp:0:0", "{}");
     do {
         status = migrate_query_status(from);
         g_assert(!strcmp(status, "setup") || !(strcmp(status, "failed")));
@@ -725,7 +735,7 @@ static void test_precopy_unix(void)
     /* Wait for the first serial output from the source */
     wait_for_serial("src_serial");
 
-    migrate(from, uri, NULL);
+    migrate(from, uri, "{}");
 
     wait_for_migration_pass(from);