migrate: Introduce a 'dc->vmsd' check to avoid segfault for --only-migratable

Commit a3a3d8c7 introduced a segfault bug while checking for
'dc->vmsd->unmigratable' which caused QEMU to crash when trying to add
devices which do no set their 'dc->vmsd' yet while initialization.
Place a 'dc->vmsd' check prior to it so that we do not segfault for
such devices.

NOTE: This doesn't compromise the functioning of --only-migratable
option as all the unmigratable devices do set their 'dc->vmsd'.

Introduce a new function check_migratable() and move the
only_migratable check inside it, also use stubs to avoid user-mode qemu
build failures.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Message-Id: <1487009088-23891-1-git-send-email-ashijeetacharya@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

hw/core/qdev.c

@@ -37,6 +37,7 @@
 #include "hw/boards.h"
 #include "hw/sysbus.h"
 #include "qapi-event.h"
+#include "migration/migration.h"
 
 int qdev_hotplug = 0;
 static bool qdev_hot_added = false;
@@ -889,6 +890,7 @@ static void device_set_realized(Object *obj, bool value, Error **errp)
     Error *local_err = NULL;
     bool unattached_parent = false;
     static int unattached_count;
+    int ret;
 
     if (dev->hotplugged && !dc->hotpluggable) {
         error_setg(errp, QERR_DEVICE_NO_HOTPLUG, object_get_typename(obj));
@@ -896,6 +898,11 @@ static void device_set_realized(Object *obj, bool value, Error **errp)
     }
 
     if (value && !dev->realized) {
+        ret = check_migratable(obj, &local_err);
+        if (ret < 0) {
+            goto fail;
+        }
+
         if (!obj->parent) {
             gchar *name = g_strdup_printf("device[%d]", unattached_count++);
 

hw/usb/bus.c

@@ -8,7 +8,6 @@
 #include "monitor/monitor.h"
 #include "trace.h"
 #include "qemu/cutils.h"
-#include "migration/migration.h"
 
 static void usb_bus_dev_print(Monitor *mon, DeviceState *qdev, int indent);
 
@@ -688,8 +687,6 @@ USBDevice *usbdevice_create(const char *cmdline)
     const char *params;
     int len;
     USBDevice *dev;
-    ObjectClass *klass;
-    DeviceClass *dc;
 
     params = strchr(cmdline,':');
     if (params) {
@@ -724,22 +721,6 @@ USBDevice *usbdevice_create(const char *cmdline)
         return NULL;
     }
 
-    klass = object_class_by_name(f->name);
-    if (klass == NULL) {
-        error_report("Device '%s' not found", f->name);
-        return NULL;
-    }
-
-    dc = DEVICE_CLASS(klass);
-
-    if (only_migratable) {
-        if (dc->vmsd->unmigratable) {
-            error_report("Device %s is not migratable, but --only-migratable "
-                         "was specified", f->name);
-            return NULL;
-        }
-    }
-
     if (f->usbdevice_init) {
         dev = f->usbdevice_init(bus, params);
     } else {

include/migration/migration.h

@@ -22,6 +22,7 @@
 #include "qapi-types.h"
 #include "exec/cpu-common.h"
 #include "qemu/coroutine_int.h"
+#include "qom/object.h"
 
 #define QEMU_VM_FILE_MAGIC           0x5145564d
 #define QEMU_VM_FILE_VERSION_COMPAT  0x00000002
@@ -313,6 +314,8 @@ int migrate_add_blocker(Error *reason, Error **errp);
  */
 void migrate_del_blocker(Error *reason);
 
+int check_migratable(Object *obj, Error **err);
+
 bool migrate_release_ram(void);
 bool migrate_postcopy_ram(void);
 bool migrate_zero_blocks(void);

migration/migration.c

@@ -1150,6 +1150,21 @@ void migrate_del_blocker(Error *reason)
     migration_blockers = g_slist_remove(migration_blockers, reason);
 }
 
+int check_migratable(Object *obj, Error **err)
+{
+    DeviceClass *dc = DEVICE_GET_CLASS(obj);
+    if (only_migratable && dc->vmsd) {
+        if (dc->vmsd->unmigratable) {
+            error_setg(err, "Device %s is not migratable, but "
+                       "--only-migratable was specified",
+                       object_get_typename(obj));
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
 void qmp_migrate_incoming(const char *uri, Error **errp)
 {
     Error *local_err = NULL;

qdev-monitor.c

@@ -29,7 +29,6 @@
 #include "qemu/error-report.h"
 #include "qemu/help_option.h"
 #include "sysemu/block-backend.h"
-#include "migration/migration.h"
 
 /*
  * Aliases were a bad idea from the start.  Let's keep them
@@ -579,14 +578,6 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
         return NULL;
     }
 
-    if (only_migratable) {
-        if (dc->vmsd->unmigratable) {
-            error_setg(errp, "Device %s is not migratable, but "
-                       "--only-migratable was specified", driver);
-            return NULL;
-        }
-    }
-
     /* find bus */
     path = qemu_opt_get(opts, "bus");
     if (path != NULL) {

stubs/vmstate.c

@@ -1,6 +1,7 @@
 #include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "migration/vmstate.h"
+#include "migration/migration.h"
 
 const VMStateDescription vmstate_dummy = {};
 
@@ -19,3 +20,8 @@ void vmstate_unregister(DeviceState *dev,
                         void *opaque)
 {
 }
+
+int check_migratable(Object *obj, Error **err)
+{
+    return 0;
+}