tests/qtest: Allow qtest_get_machines to use an alternate QEMU binary

We're adding support for using more than one QEMU binary in
tests. Modify qtest_get_machines() to take an environment variable
that contains the QEMU binary path.

Since the function keeps a cache of the machines list in the form of a
static variable, refresh it any time the environment variable changes.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231018192741.25885-4-farosas@suse.de>

tests/qtest/libqtest.c

@@ -1468,13 +1468,26 @@ struct MachInfo {
     char *alias;
 };
 
+static void qtest_free_machine_list(struct MachInfo *machines)
+{
+    if (machines) {
+        for (int i = 0; machines[i].name != NULL; i++) {
+            g_free(machines[i].name);
+            g_free(machines[i].alias);
+        }
+
+        g_free(machines);
+    }
+}
+
 /*
  * Returns an array with pointers to the available machine names.
  * The terminating entry has the name set to NULL.
  */
-static struct MachInfo *qtest_get_machines(void)
+static struct MachInfo *qtest_get_machines(const char *var)
 {
     static struct MachInfo *machines;
+    static char *qemu_var;
     QDict *response, *minfo;
     QList *list;
     const QListEntry *p;
@@ -1483,11 +1496,19 @@ static struct MachInfo *qtest_get_machines(void)
     QTestState *qts;
     int idx;
 
+    if (g_strcmp0(qemu_var, var)) {
+        qemu_var = g_strdup(var);
+
+        /* new qemu, clear the cache */
+        qtest_free_machine_list(machines);
+        machines = NULL;
+    }
+
     if (machines) {
         return machines;
     }
 
-    qts = qtest_init("-machine none");
+    qts = qtest_init_with_env(qemu_var, "-machine none");
     response = qtest_qmp(qts, "{ 'execute': 'query-machines' }");
     g_assert(response);
     list = qdict_get_qlist(response, "return");
@@ -1528,7 +1549,7 @@ void qtest_cb_for_every_machine(void (*cb)(const char *machine),
     struct MachInfo *machines;
     int i;
 
-    machines = qtest_get_machines();
+    machines = qtest_get_machines(NULL);
 
     for (i = 0; machines[i].name != NULL; i++) {
         /* Ignore machines that cannot be used for qtests */
@@ -1549,7 +1570,7 @@ bool qtest_has_machine(const char *machine)
     struct MachInfo *machines;
     int i;
 
-    machines = qtest_get_machines();
+    machines = qtest_get_machines(NULL);
 
     for (i = 0; machines[i].name != NULL; i++) {
         if (g_str_equal(machine, machines[i].name) ||