migration: Add validate-uuid capability

This capability realizes simple source validation by UUID.
It's useful for live migration between hosts.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Message-Id: <20190903162246.18524-2-yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/migration.c

@@ -2140,6 +2140,15 @@ bool migrate_ignore_shared(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_X_IGNORE_SHARED];
 }
 
+bool migrate_validate_uuid(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_VALIDATE_UUID];
+}
+
 bool migrate_use_events(void)
 {
     MigrationState *s;

migration/migration.h

@@ -290,6 +290,7 @@ bool migrate_postcopy_ram(void);
 bool migrate_zero_blocks(void);
 bool migrate_dirty_bitmaps(void);
 bool migrate_ignore_shared(void);
+bool migrate_validate_uuid(void);
 
 bool migrate_auto_converge(void);
 bool migrate_use_multifd(void);

migration/savevm.c

@@ -256,6 +256,7 @@ typedef struct SaveState {
     uint32_t target_page_bits;
     uint32_t caps_count;
     MigrationCapability *capabilities;
+    QemuUUID uuid;
 } SaveState;
 
 static SaveState savevm_state = {
@@ -307,6 +308,7 @@ static int configuration_pre_save(void *opaque)
             state->capabilities[j++] = i;
         }
     }
+    state->uuid = qemu_uuid;
 
     return 0;
 }
@@ -464,6 +466,48 @@ static const VMStateDescription vmstate_capabilites = {
     }
 };
 
+static bool vmstate_uuid_needed(void *opaque)
+{
+    return qemu_uuid_set && migrate_validate_uuid();
+}
+
+static int vmstate_uuid_post_load(void *opaque, int version_id)
+{
+    SaveState *state = opaque;
+    char uuid_src[UUID_FMT_LEN + 1];
+    char uuid_dst[UUID_FMT_LEN + 1];
+
+    if (!qemu_uuid_set) {
+        /*
+         * It's warning because user might not know UUID in some cases,
+         * e.g. load an old snapshot
+         */
+        qemu_uuid_unparse(&state->uuid, uuid_src);
+        warn_report("UUID is received %s, but local uuid isn't set",
+                     uuid_src);
+        return 0;
+    }
+    if (!qemu_uuid_is_equal(&state->uuid, &qemu_uuid)) {
+        qemu_uuid_unparse(&state->uuid, uuid_src);
+        qemu_uuid_unparse(&qemu_uuid, uuid_dst);
+        error_report("UUID received is %s and local is %s", uuid_src, uuid_dst);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static const VMStateDescription vmstate_uuid = {
+    .name = "configuration/uuid",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = vmstate_uuid_needed,
+    .post_load = vmstate_uuid_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8_ARRAY_V(uuid.data, SaveState, sizeof(QemuUUID), 1),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_configuration = {
     .name = "configuration",
     .version_id = 1,
@@ -478,6 +522,7 @@ static const VMStateDescription vmstate_configuration = {
     .subsections = (const VMStateDescription*[]) {
         &vmstate_target_page_bits,
         &vmstate_capabilites,
+        &vmstate_uuid,
         NULL
     }
 };

qapi/migration.json

@@ -415,6 +415,9 @@
 #
 # @x-ignore-shared: If enabled, QEMU will not migrate shared memory (since 4.0)
 #
+# @validate-uuid: Send the UUID of the source to allow the destination
+#                 to ensure it is the same. (since 4.2)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
@@ -422,7 +425,7 @@
            'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
            'block', 'return-path', 'pause-before-switchover', 'multifd',
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
-           'x-ignore-shared' ] }
+           'x-ignore-shared', 'validate-uuid' ] }
 
 ##
 # @MigrationCapabilityStatus: