[Qemu-block] [PATCH 1/1] blockdev: n-ary bitmap merge

[John Snow]

It might be nice to have an all-or-nothing merge command that either
succeeds in merging all bitmaps or fails for all of them. This way,
when assembling bitmaps that represent arbitrary points in time from
component bitmaps, we always know the state of the target bitmap even
in cases of failure.

Signed-off-by: John Snow <address@hidden>
---
 blockdev.c           | 40 ++++++++++++++++++++++++++++++----------
 qapi/block-core.json | 10 +++++-----
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 041f5d594f..4d60d0a03c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3054,34 +3054,54 @@ void qmp_x_block_dirty_bitmap_disable(const char *node, 
const char *name,
     bdrv_disable_dirty_bitmap(bitmap);
 }
 
-void qmp_x_block_dirty_bitmap_merge(const char *node, const char *dst_name,
-                                    const char *src_name, Error **errp)
+void qmp_x_block_dirty_bitmap_merge(const char *node, const char *target,
+                                    strList *bitmaps, Error **errp)
 {
     BlockDriverState *bs;
-    BdrvDirtyBitmap *dst, *src;
+    BdrvDirtyBitmap *dst, *src, *anon;
+    strList *lst;
+    Error *local_err = NULL;
 
-    dst = block_dirty_bitmap_lookup(node, dst_name, &bs, errp);
+    dst = block_dirty_bitmap_lookup(node, target, &bs, errp);
     if (!dst) {
         return;
     }
 
     if (bdrv_dirty_bitmap_frozen(dst)) {
         error_setg(errp, "Bitmap '%s' is frozen and cannot be modified",
-                   dst_name);
+                   target);
         return;
     } else if (bdrv_dirty_bitmap_readonly(dst)) {
         error_setg(errp, "Bitmap '%s' is readonly and cannot be modified",
-                   dst_name);
+                   target);
         return;
     }
 
-    src = bdrv_find_dirty_bitmap(bs, src_name);
-    if (!src) {
-        error_setg(errp, "Dirty bitmap '%s' not found", src_name);
+    anon = bdrv_create_dirty_bitmap(bs, bdrv_dirty_bitmap_granularity(dst),
+                                    NULL, errp);
+    if (!anon) {
         return;
     }
 
-    bdrv_merge_dirty_bitmap(dst, src, errp);
+    /* Aggregate bitmaps to anonymous temp bitmap */
+    for (lst = bitmaps; lst; lst = lst->next) {
+      src = bdrv_find_dirty_bitmap(bs, lst->value);
+      if (!src) {
+          error_setg(errp, "Dirty bitmap '%s' not found", lst->value);
+          goto out;
+      }
+      bdrv_merge_dirty_bitmap(anon, src, &local_err);
+      if (local_err) {
+          error_propagate(errp, local_err);
+          goto out;
+      }
+    }
+
+    /* Merge into dst; dst is unchanged on failure */
+    bdrv_merge_dirty_bitmap(dst, anon, errp);
+
+out:
+    bdrv_release_dirty_bitmap(bs, anon);
 }
 
 BlockDirtyBitmapSha256 *qmp_x_debug_block_dirty_bitmap_sha256(const char *node,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index fff23fc82b..83402da7e7 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1749,14 +1749,14 @@
 #
 # @node: name of device/node which the bitmap is tracking
 #
-# @dst_name: name of the destination dirty bitmap
+# @target: name of the destination dirty bitmap
 #
-# @src_name: name of the source dirty bitmap
+# @bitmaps: name(s) of the source dirty bitmap(s)
 #
 # Since: 3.0
 ##
 { 'struct': 'BlockDirtyBitmapMerge',
-  'data': { 'node': 'str', 'dst_name': 'str', 'src_name': 'str' } }
+  'data': { 'node': 'str', 'target': 'str', 'bitmaps': ['str'] } }
 
 ##
 # @block-dirty-bitmap-add:
@@ -1884,8 +1884,8 @@
 # Example:
 #
 # -> { "execute": "x-block-dirty-bitmap-merge",
-#      "arguments": { "node": "drive0", "dst_name": "bitmap0",
-#                     "src_name": "bitmap1" } }
+#      "arguments": { "node": "drive0", "target": "bitmap0",
+#                     "bitmaps": ["bitmap1"] } }
 # <- { "return": {} }
 #
 ##
-- 
2.14.3