vmstate: Add support for alias ID

Some legacy users (mostly PC devices) of vmstate_register manage
instance IDs on their own, and that unfortunately in a way that is
incompatible with automatically generated ones. This so far prevents
switching those users to vmstates that are registered by qdev.

To establish a migration path, this patch introduces the concept of
alias IDs. They can be passed to an extended vmstate registration
service, and qdev provides a set service to be used during device init.
find_se will consider the alias in addition to the default ID. We can
then start generating the default ID automatically and writing it on
vmsave, thus converting that format without breaking support for upward
migration.

The user is required specify the highest vmstate version for which the
alias is required. Once this version falls behind the minimum required
for a specific vmstate, an assertion triggers to motivate cleaning up
the obsolete alias.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

diff --git a/hw/hw.h b/hw/hw.h
index 2d397243d193eabef27062dd07e4e068599791bb..fc2d1849d77a984a1d177b79ddd7e662e6437fae 100644 (file)
--- a/hw/hw.h
+++ b/hw/hw.h
@@ -758,5 +758,9 @@ extern void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
                                void *opaque);
 extern int vmstate_register(int instance_id, const VMStateDescription *vmsd,
                             void *base);
+extern int vmstate_register_with_alias_id(int instance_id,
+                                          const VMStateDescription *vmsd,
+                                          void *base, int alias_id,
+                                          int required_for_version);
 void vmstate_unregister(const VMStateDescription *vmsd, void *opaque);
 #endif

diff --git a/hw/qdev.c b/hw/qdev.c
index d3bf0fa43dc41d392de4ee27ce8ea521b298dab9..af174869761423e241c3857b1372c4a1bddab95a 100644 (file)
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -93,6 +93,7 @@ static DeviceState *qdev_create_from_info(BusState *bus, DeviceInfo *info)
         assert(bus->allow_hotplug);
         dev->hotplugged = 1;
     }
+    dev->instance_id_alias = -1;
     dev->state = DEV_STATE_CREATED;
     return dev;
 }
@@ -278,12 +279,23 @@ int qdev_init(DeviceState *dev)
         return rc;
     }
     qemu_register_reset(qdev_reset, dev);
-    if (dev->info->vmsd)
-        vmstate_register(-1, dev->info->vmsd, dev);
+    if (dev->info->vmsd) {
+        vmstate_register_with_alias_id(-1, dev->info->vmsd, dev,
+                                       dev->instance_id_alias,
+                                       dev->alias_required_for_version);
+    }
     dev->state = DEV_STATE_INITIALIZED;
     return 0;
 }
 
+void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
+                                 int required_for_version)
+{
+    assert(dev->state == DEV_STATE_CREATED);
+    dev->instance_id_alias = alias_id;
+    dev->alias_required_for_version = required_for_version;
+}
+
 int qdev_unplug(DeviceState *dev)
 {
     if (!dev->parent_bus->allow_hotplug) {

diff --git a/hw/qdev.h b/hw/qdev.h
index d8fbc739a0550401b360765753488d9ab02c8e0a..a44060e54cd02525a7462abda9cd52c3f3dc1a65 100644 (file)
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -44,6 +44,8 @@ struct DeviceState {
     QLIST_HEAD(, BusState) child_bus;
     int num_child_bus;
     QLIST_ENTRY(DeviceState) sibling;
+    int instance_id_alias;
+    int alias_required_for_version;
 };
 
 typedef void (*bus_dev_printfn)(Monitor *mon, DeviceState *dev, int indent);
@@ -112,6 +114,8 @@ int qdev_device_help(QemuOpts *opts);
 DeviceState *qdev_device_add(QemuOpts *opts);
 int qdev_init(DeviceState *dev) QEMU_WARN_UNUSED_RESULT;
 void qdev_init_nofail(DeviceState *dev);
+void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
+                                 int required_for_version);
 int qdev_unplug(DeviceState *dev);
 void qdev_free(DeviceState *dev);
 int qdev_simple_unplug_cb(DeviceState *dev);

diff --git a/savevm.c b/savevm.c
index 74e553c53debe0ffb97f87fe2704528773b33d27..dc20390b8f459ac74adf3642b6cf8a16374f8e7c 100644 (file)
--- a/savevm.c
+++ b/savevm.c
@@ -991,6 +991,7 @@ typedef struct SaveStateEntry {
     QTAILQ_ENTRY(SaveStateEntry) entry;
     char idstr[256];
     int instance_id;
+    int alias_id;
     int version_id;
     int section_id;
     SaveSetParamsHandler *set_params;
@@ -1079,11 +1080,16 @@ void unregister_savevm(const char *idstr, void *opaque)
     }
 }
 
-int vmstate_register(int instance_id, const VMStateDescription *vmsd,
-                     void *opaque)
+int vmstate_register_with_alias_id(int instance_id,
+                                   const VMStateDescription *vmsd,
+                                   void *opaque, int alias_id,
+                                   int required_for_version)
 {
     SaveStateEntry *se;
 
+    /* If this triggers, alias support can be dropped for the vmsd. */
+    assert(alias_id == -1 || required_for_version >= vmsd->minimum_version_id);
+
     se = qemu_mallocz(sizeof(SaveStateEntry));
     pstrcpy(se->idstr, sizeof(se->idstr), vmsd->name);
     se->version_id = vmsd->version_id;
@@ -1093,6 +1099,7 @@ int vmstate_register(int instance_id, const VMStateDescription *vmsd,
     se->load_state = NULL;
     se->opaque = opaque;
     se->vmsd = vmsd;
+    se->alias_id = alias_id;
 
     if (instance_id == -1) {
         se->instance_id = calculate_new_instance_id(vmsd->name);
@@ -1104,6 +1111,12 @@ int vmstate_register(int instance_id, const VMStateDescription *vmsd,
     return 0;
 }
 
+int vmstate_register(int instance_id, const VMStateDescription *vmsd,
+                     void *opaque)
+{
+    return vmstate_register_with_alias_id(instance_id, vmsd, opaque, -1, 0);
+}
+
 void vmstate_unregister(const VMStateDescription *vmsd, void *opaque)
 {
     SaveStateEntry *se, *new_se;
@@ -1433,7 +1446,8 @@ static SaveStateEntry *find_se(const char *idstr, int instance_id)
 
     QTAILQ_FOREACH(se, &savevm_handlers, entry) {
         if (!strcmp(se->idstr, idstr) &&
-            instance_id == se->instance_id)
+            (instance_id == se->instance_id ||
+             instance_id == se->alias_id))
             return se;
     }
     return NULL;