qemu-option: Introduce default mechanism

index a303f87..4626ccf 100644
@@ -603,7 +603,8 @@ static void qemu_opt_del(QemuOpt *opt)
     g_free(opt);
 }
 
-int qemu_opt_set(QemuOpts *opts, const char *name, const char *value)
+static int opt_set(QemuOpts *opts, const char *name, const char *value,
+                   bool prepend)
 {
     QemuOpt *opt;
     const QemuOptDesc *desc = opts->list->desc;

@@ -626,7 +627,11 @@ int qemu_opt_set(QemuOpts *opts, const char *name, const char *value)
     opt = g_malloc0(sizeof(*opt));
     opt->name = g_strdup(name);
     opt->opts = opts;
-    QTAILQ_INSERT_TAIL(&opts->head, opt, next);
+    if (prepend) {
+        QTAILQ_INSERT_HEAD(&opts->head, opt, next);
+    } else {
+        QTAILQ_INSERT_TAIL(&opts->head, opt, next);
+    }
     if (desc[i].name != NULL) {
         opt->desc = desc+i;
     }

@@ -640,6 +645,11 @@ int qemu_opt_set(QemuOpts *opts, const char *name, const char *value)
     return 0;
 }
 
+int qemu_opt_set(QemuOpts *opts, const char *name, const char *value)
+{
+    return opt_set(opts, name, value, false);
+}
+
 int qemu_opt_set_bool(QemuOpts *opts, const char *name, bool val)
 {
     QemuOpt *opt;

@@ -691,6 +701,9 @@ QemuOpts *qemu_opts_find(QemuOptsList *list, const char *id)
 
     QTAILQ_FOREACH(opts, &list->head, next) {
         if (!opts->id) {
+            if (!id) {
+                return opts;
+            }
             continue;
         }
         if (strcmp(opts->id, id) != 0) {

@@ -806,7 +819,8 @@ int qemu_opts_print(QemuOpts *opts, void *dummy)
     return 0;
 }
 
-int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname)
+static int opts_do_parse(QemuOpts *opts, const char *params,
+                         const char *firstname, bool prepend)
 {
     char option[128], value[1024];
     const char *p,*pe,*pc;

@@ -841,7 +855,7 @@ int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname
         }
         if (strcmp(option, "id") != 0) {
             /* store and parse */
-            if (qemu_opt_set(opts, option, value) == -1) {
+            if (opt_set(opts, option, value, prepend) == -1) {
                 return -1;
             }
         }

@@ -852,8 +866,13 @@ int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname
     return 0;
 }
 
-QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params,
-                          int permit_abbrev)
+int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname)
+{
+    return opts_do_parse(opts, params, firstname, false);
+}
+
+static QemuOpts *opts_parse(QemuOptsList *list, const char *params,
+                            int permit_abbrev, bool defaults)
 {
     const char *firstname;
     char value[1024], *id = NULL;

@@ -870,11 +889,19 @@ QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params,
         get_opt_value(value, sizeof(value), p+4);
         id = value;
     }
-    opts = qemu_opts_create(list, id, 1);
+    if (defaults) {
+        if (!id && !QTAILQ_EMPTY(&list->head)) {
+            opts = qemu_opts_find(list, NULL);
+        } else {
+            opts = qemu_opts_create(list, id, 0);
+        }
+    } else {
+        opts = qemu_opts_create(list, id, 1);
+    }
     if (opts == NULL)
         return NULL;
 
-    if (qemu_opts_do_parse(opts, params, firstname) != 0) {
+    if (opts_do_parse(opts, params, firstname, defaults) != 0) {
         qemu_opts_del(opts);
         return NULL;
     }

@@ -882,6 +909,21 @@ QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params,
     return opts;
 }
 
+QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params,
+                          int permit_abbrev)
+{
+    return opts_parse(list, params, permit_abbrev, false);
+}
+
+void qemu_opts_set_defaults(QemuOptsList *list, const char *params,
+                            int permit_abbrev)
+{
+    QemuOpts *opts;
+
+    opts = opts_parse(list, params, permit_abbrev, true);
+    assert(opts);
+}
+
 static void qemu_opts_from_qdict_1(const char *key, QObject *obj, void *opaque)
 {
     char buf[32];

index 07958e4..e6f61e6 100644
@@ -125,6 +125,8 @@ void qemu_opts_del(QemuOpts *opts);
 int qemu_opts_validate(QemuOpts *opts, const QemuOptDesc *desc);
 int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname);
 QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params, int permit_abbrev);
+void qemu_opts_set_defaults(QemuOptsList *list, const char *params,
+                            int permit_abbrev);
 QemuOpts *qemu_opts_from_qdict(QemuOptsList *list, const QDict *qdict);
 QDict *qemu_opts_to_qdict(QemuOpts *opts, QDict *qdict);
 

index 6af0f83..138f6bc 100644
@@ -3153,21 +3153,8 @@ int main(int argc, char **argv, char **envp)
      * specified either by the configuration file or by the command line.
      */
     if (machine->default_machine_opts) {
-        QemuOptsList *list = qemu_find_opts("machine");
-        const char *p = NULL;
-
-        if (!QTAILQ_EMPTY(&list->head)) {
-            p = qemu_opt_get(QTAILQ_FIRST(&list->head), "accel");
-        }
-        if (p == NULL) {
-            qemu_opts_reset(list);
-            opts = qemu_opts_parse(list, machine->default_machine_opts, 0);
-            if (!opts) {
-                fprintf(stderr, "parse error for machine %s: %s\n",
-                        machine->name, machine->default_machine_opts);
-                exit(1);
-            }
-        }
+        qemu_opts_set_defaults(qemu_find_opts("machine"),
+                               machine->default_machine_opts, 0);
     }
 
     qemu_opts_foreach(qemu_find_opts("device"), default_driver_check, NULL, 0);