1 files changed, 94 insertions, 0 deletions
diff --git a/migration/block-active.c b/migration/block-active.c
new file mode 100644
index 0000000000..d477cf8182
--- /dev/null
+++ b/migration/block-active.c
@@ -0,0 +1,94 @@
+/*
+ * Block activation tracking for migration purpose
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * Copyright (C) 2024 Red Hat, Inc.
+ */
+#include "qemu/osdep.h"
+#include "block/block.h"
+#include "qapi/error.h"
+#include "migration/migration.h"
+#include "qemu/error-report.h"
+#include "trace.h"
+
+/*
+ * Migration-only cache to remember the block layer activation status.
+ * Protected by BQL.
+ *
+ * We need this because..
+ *
+ * - Migration can fail after block devices are invalidated (during
+ *   switchover phase).  When that happens, we need to be able to recover
+ *   the block drive status by re-activating them.
+ *
+ * - Currently bdrv_inactivate_all() is not safe to be invoked on top of
+ *   invalidated drives (even if bdrv_activate_all() is actually safe to be
+ *   called any time!).  It means remembering this could help migration to
+ *   make sure it won't invalidate twice in a row, crashing QEMU.  It can
+ *   happen when we migrate a PAUSED VM from host1 to host2, then migrate
+ *   again to host3 without starting it.  TODO: a cleaner solution is to
+ *   allow safe invoke of bdrv_inactivate_all() at anytime, like
+ *   bdrv_activate_all().
+ *
+ * For freshly started QEMU, the flag is initialized to TRUE reflecting the
+ * scenario where QEMU owns block device ownerships.
+ *
+ * For incoming QEMU taking a migration stream, the flag is initialized to
+ * FALSE reflecting that the incoming side doesn't own the block devices,
+ * not until switchover happens.
+ */
+static bool migration_block_active;
+
+/* Setup the disk activation status */
+void migration_block_active_setup(bool active)
+{
+    migration_block_active = active;
+}
+
+bool migration_block_activate(Error **errp)
+{
+    ERRP_GUARD();
+
+    assert(bql_locked());
+
+    if (migration_block_active) {
+        trace_migration_block_activation("active-skipped");
+        return true;
+    }
+
+    trace_migration_block_activation("active");
+
+    bdrv_activate_all(errp);
+    if (*errp) {
+        error_report_err(error_copy(*errp));
+        return false;
+    }
+
+    migration_block_active = true;
+    return true;
+}
+
+bool migration_block_inactivate(void)
+{
+    int ret;
+
+    assert(bql_locked());
+
+    if (!migration_block_active) {
+        trace_migration_block_activation("inactive-skipped");
+        return true;
+    }
+
+    trace_migration_block_activation("inactive");
+
+    ret = bdrv_inactivate_all();
+    if (ret) {
+        error_report("%s: bdrv_inactivate_all() failed: %d",
+                     __func__, ret);
+        return false;
+    }
+
+    migration_block_active = false;
+    return true;
+}