[PATCH 3/4] block: improve block_dirty_bitmap_merge(): don't allocate extra bitmap

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

We don't need extra bitmap. All we need is to backup the original
bitmap when we do first merge. So, drop extra temporary bitmap and work
directly with target and backup.

Note that block_dirty_bitmap_merge() semantics changed: on failure
target may be modified now, and caller should call
block_dirty_bitmap_restore() if needed. The only caller is
qmp_transaction() and ->abort() is called for failed action. So, we are
OK.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/monitor/bitmap-qmp-cmds.c | 31 +++++++++----------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/block/monitor/bitmap-qmp-cmds.c b/block/monitor/bitmap-qmp-cmds.c
index a94aaa9fb3..2ce1b4e455 100644
--- a/block/monitor/bitmap-qmp-cmds.c
+++ b/block/monitor/bitmap-qmp-cmds.c
@@ -252,12 +252,15 @@ void qmp_block_dirty_bitmap_disable(const char *node, const char *name,
     bdrv_disable_dirty_bitmap(bitmap);
 }
 
+/*
+ * On failure target may be modified. In this case @backup is set.
+ */
 BdrvDirtyBitmap *block_dirty_bitmap_merge(const char *node, const char *target,
                                           BlockDirtyBitmapMergeSourceList *bms,
                                           HBitmap **backup, Error **errp)
 {
     BlockDriverState *bs;
-    BdrvDirtyBitmap *dst, *src, *anon;
+    BdrvDirtyBitmap *dst, *src;
     BlockDirtyBitmapMergeSourceList *lst;
 
     dst = block_dirty_bitmap_lookup(node, target, &bs, errp);
@@ -265,12 +268,6 @@ BdrvDirtyBitmap *block_dirty_bitmap_merge(const char *node, const char *target,
         return NULL;
     }
 
-    anon = bdrv_create_dirty_bitmap(bs, bdrv_dirty_bitmap_granularity(dst),
-                                    NULL, errp);
-    if (!anon) {
-        return NULL;
-    }
-
     for (lst = bms; lst; lst = lst->next) {
         switch (lst->value->type) {
             const char *name, *node;
@@ -279,8 +276,7 @@ BdrvDirtyBitmap *block_dirty_bitmap_merge(const char *node, const char *target,
             src = bdrv_find_dirty_bitmap(bs, name);
             if (!src) {
                 error_setg(errp, "Dirty bitmap '%s' not found", name);
-                dst = NULL;
-                goto out;
+                return NULL;
             }
             break;
         case QTYPE_QDICT:
@@ -288,28 +284,19 @@ BdrvDirtyBitmap *block_dirty_bitmap_merge(const char *node, const char *target,
             name = lst->value->u.external.name;
             src = block_dirty_bitmap_lookup(node, name, NULL, errp);
             if (!src) {
-                dst = NULL;
-                goto out;
+                return NULL;
             }
             break;
         default:
             abort();
         }
 
-        if (!bdrv_merge_dirty_bitmap(anon, src, NULL, errp)) {
-            dst = NULL;
-            goto out;
+        if (!bdrv_merge_dirty_bitmap(dst, src, backup, errp)) {
+            return NULL;
         }
+        backup = NULL; /* Set once by first bdrv_merge_dirty_bitmap() call */
     }
 
-    /* Merge into dst; dst is unchanged on failure. */
-    if (!bdrv_merge_dirty_bitmap(dst, anon, backup, errp)) {
-        dst = NULL;
-        goto out;
-    }
-
- out:
-    bdrv_release_dirty_bitmap(anon);
     return dst;
 }
 
-- 
2.31.1