Add boot-once support

This allows to specify an exceptional boot order only for the first
startup of the guest. After reboot, qemu will switch back to the default
order (or what was specified via 'order='). Makes installing from CD
images and then booting the freshly set up harddisk more handy.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

vl.c

@@ -2402,6 +2402,16 @@ static int parse_bootdevices(char *devices)
     return bitmap;
 }
 
+static void restore_boot_devices(void *opaque)
+{
+    char *standard_boot_devices = opaque;
+
+    qemu_boot_set(standard_boot_devices);
+
+    qemu_unregister_reset(restore_boot_devices, standard_boot_devices);
+    qemu_free(standard_boot_devices);
+}
+
 static void numa_add(const char *optarg)
 {
     char option[128];
@@ -5111,9 +5121,10 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_boot:
                 {
                     static const char * const params[] = {
-                        "order", NULL
+                        "order", "once", NULL
                     };
                     char buf[sizeof(boot_devices)];
+                    char *standard_boot_devices;
                     int legacy = 0;
 
                     if (!strchr(optarg, '=')) {
@@ -5131,6 +5142,16 @@ int main(int argc, char **argv, char **envp)
                         boot_devices_bitmap = parse_bootdevices(buf);
                         pstrcpy(boot_devices, sizeof(boot_devices), buf);
                     }
+                    if (!legacy) {
+                        if (get_param_value(buf, sizeof(buf),
+                                            "once", optarg)) {
+                            boot_devices_bitmap |= parse_bootdevices(buf);
+                            standard_boot_devices = qemu_strdup(boot_devices);
+                            pstrcpy(boot_devices, sizeof(boot_devices), buf);
+                            qemu_register_reset(restore_boot_devices,
+                                                standard_boot_devices);
+                        }
+                    }
                 }
                 break;
             case QEMU_OPTION_fda: