commit 6e9f21a2aa8a78bc9a512a836a40c79fe50dd2b4
author Peter Krempa <pkrempa@redhat.com> Fri Feb 12 18:34:24 2021 +0100
committer Eric Blake <eblake@redhat.com> Fri Feb 12 15:24:36 2021 -0600
tree 749863cda552af19233d6556c32469310713c565
parent 0d1e450c7b3117ee635a00c81d9a92666ebc7ffa

migration: dirty-bitmap: Allow control of bitmap persistence

Bitmap's source persistence is transported over the migration stream and
the destination mirrors it. In some cases the destination might want to
persist bitmaps which are not persistent on the source (e.g. the result
of merging bitmaps from a number of layers on the source when migrating
into a squashed image) but currently it would need to create another set
of persistent bitmaps and merge them.

This patch adds a 'transform' property to the alias map which allows
overriding the persistence of migrated bitmaps both on the source and
destination sides.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Message-Id: <b20afb675917b86f6359ac3591166ac6d4233573.1613150869.git.pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: grammar tweaks, drop dead conditional]
Signed-off-by: Eric Blake <eblake@redhat.com>

migration/block-dirty-bitmap.c

diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index b39c13c..9750936 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -150,6 +150,7 @@
     BdrvDirtyBitmap *bitmap;
 
     bool before_vm_start_handled; /* set in dirty_bitmap_mig_before_vm_start */
+    BitmapMigrationBitmapAlias *bmap_inner;
 
     /*
      * cancelled
@@ -529,6 +530,7 @@
     }
 
     FOR_EACH_DIRTY_BITMAP(bs, bitmap) {
+        BitmapMigrationBitmapAliasTransform *bitmap_transform = NULL;
         bitmap_name = bdrv_dirty_bitmap_name(bitmap);
         if (!bitmap_name) {
             continue;
@@ -549,6 +551,9 @@
             }
 
             bitmap_alias = bmap_inner->alias;
+            if (bmap_inner->has_transform) {
+                bitmap_transform = bmap_inner->transform;
+            }
         } else {
             if (strlen(bitmap_name) > UINT8_MAX) {
                 error_report("Cannot migrate bitmap '%s' on node '%s': "
@@ -574,8 +579,15 @@
         if (bdrv_dirty_bitmap_enabled(bitmap)) {
             dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_ENABLED;
         }
-        if (bdrv_dirty_bitmap_get_persistence(bitmap)) {
-            dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
+        if (bitmap_transform &&
+            bitmap_transform->has_persistent) {
+            if (bitmap_transform->persistent) {
+                dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
+            }
+        } else {
+            if (bdrv_dirty_bitmap_get_persistence(bitmap)) {
+                dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
+            }
         }
 
         QSIMPLEQ_INSERT_TAIL(&s->dbms_list, dbms, entry);
@@ -783,6 +795,7 @@
     uint32_t granularity = qemu_get_be32(f);
     uint8_t flags = qemu_get_byte(f);
     LoadBitmapState *b;
+    bool persistent;
 
     if (s->cancelled) {
         return 0;
@@ -807,7 +820,15 @@
         return -EINVAL;
     }
 
-    if (flags & DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT) {
+    if (s->bmap_inner &&
+        s->bmap_inner->has_transform &&
+        s->bmap_inner->transform->has_persistent) {
+        persistent = s->bmap_inner->transform->persistent;
+    } else {
+        persistent = flags & DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
+    }
+
+    if (persistent) {
         bdrv_dirty_bitmap_set_persistence(s->bitmap, true);
     }
 
@@ -1091,6 +1112,8 @@
             } else {
                 bitmap_name = bmap_inner->name;
             }
+
+            s->bmap_inner = bmap_inner;
         }
 
         if (!s->cancelled) {

qapi/migration.json

diff --git a/qapi/migration.json b/qapi/migration.json
index ce14d78..6e5943f 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -537,6 +537,19 @@
             { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' } ] }
 
 ##
+# @BitmapMigrationBitmapAliasTransform:
+#
+# @persistent: If present, the bitmap will be made persistent
+#              or transient depending on this parameter.
+#
+# Since: 6.0
+##
+{ 'struct': 'BitmapMigrationBitmapAliasTransform',
+  'data': {
+      '*persistent': 'bool'
+  } }
+
+##
 # @BitmapMigrationBitmapAlias:
 #
 # @name: The name of the bitmap.
@@ -544,12 +557,16 @@
 # @alias: An alias name for migration (for example the bitmap name on
 #         the opposite site).
 #
+# @transform: Allows the modification of the migrated bitmap.
+#             (since 6.0)
+#
 # Since: 5.2
 ##
 { 'struct': 'BitmapMigrationBitmapAlias',
   'data': {
       'name': 'str',
-      'alias': 'str'
+      'alias': 'str',
+      '*transform': 'BitmapMigrationBitmapAliasTransform'
   } }
 
 ##