[libvirt] [PATCH 10/19] qemu: snapshot: Propagate active bitmaps through external snapshots

[Peter Krempa]

Re-create any active persistent bitmap in the snapshot overlay image so
that tracking for a checkpoint is persisted. While this basically
duplicates data in the allocation map it's currently the only possible
way as qemu can't mirror the allocation map into a dirty bitmap if we'd
ever want to do a backup.

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 src/qemu/qemu_driver.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index d2769dab1a..8ccd6b7c97 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -15223,6 +15223,42 @@ qemuDomainSnapshotDiskCleanup(qemuDomainSnapshotDiskDataPtr data,
 }


+/**
+ * qemuDomainSnapshotDiskBitmapsPropagate:
+ *
+ * This function propagates any active persistent bitmap present in the original
+ * image into the new snapshot. We leave the original bitmap active as in cases
+ * when the overlay is discarded (snapshot revert with abandoning the history)
+ * everything works as expected.
+ * */
+static int
+qemuDomainSnapshotDiskBitmapsPropagate(qemuDomainSnapshotDiskDataPtr dd,
+                                       virJSONValuePtr actions,
+                                       virHashTablePtr blockNamedNodeData)
+{
+    qemuBlockNamedNodeDataPtr entry;
+    size_t i;
+
+    if (!(entry = virHashLookup(blockNamedNodeData, dd->disk->src->nodeformat)))
+        return 0;
+
+    for (i = 0; i < entry->nbitmaps; i++) {
+        qemuBlockNamedNodeDataBitmapPtr bitmap = entry->bitmaps[i];
+
+        /* we don't care about temporary, inconsistent, or disabled bitmaps */
+        if (!bitmap->persistent || !bitmap->recording || bitmap->inconsistent)
+            continue;
+
+        if (qemuMonitorTransactionBitmapAdd(actions, dd->src->nodeformat,
+                                            bitmap->name, true, false,
+                                            bitmap->granularity) < 0)
+            return -1;
+    }
+
+    return 0;
+}
+
+
 static int
 qemuDomainSnapshotDiskPrepareOneBlockdev(virQEMUDriverPtr driver,
                                          virDomainObjPtr vm,
@@ -15364,6 +15400,9 @@ qemuDomainSnapshotDiskPrepareOne(virQEMUDriverPtr driver,
                                                      blockNamedNodeData, asyncJob) < 0)
             return -1;

+        if (qemuDomainSnapshotDiskBitmapsPropagate(dd, actions, blockNamedNodeData) < 0)
+            return -1;
+
         if (qemuBlockSnapshotAddBlockdev(actions, dd->disk, dd->src) < 0)
             return -1;
     } else {
-- 
2.23.0