blockdev: n-ary bitmap merge

Especially outside of transactions, it is helpful to provide
all-or-nothing semantics for bitmap merges. This facilitates
the coalescing of multiple bitmaps into a single target for
the "checkpoint" interpretation when assembling bitmaps that
represent arbitrary points in time from component bitmaps.

This is an incompatible change from the preliminary version
of the API.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20181221093529.23855-4-jsnow@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

2 files changed, 62 insertions, 35 deletions

diff --git a/blockdev.c b/blockdev.c
index 3d46f8191f..f7bf48dfe7 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2119,33 +2119,28 @@ static void block_dirty_bitmap_disable_abort(BlkActionState *common)
     }
 }
 
+static BdrvDirtyBitmap *do_block_dirty_bitmap_merge(const char *node,
+                                                    const char *target,
+                                                    strList *bitmaps,
+                                                    HBitmap **backup,
+                                                    Error **errp);
+
 static void block_dirty_bitmap_merge_prepare(BlkActionState *common,
                                              Error **errp)
 {
     BlockDirtyBitmapMerge *action;
     BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
                                              common, common);
-    BdrvDirtyBitmap *merge_source;
 
     if (action_check_completion_mode(common, errp) < 0) {
         return;
     }
 
     action = common->action->u.x_block_dirty_bitmap_merge.data;
-    state->bitmap = block_dirty_bitmap_lookup(action->node,
-                                              action->dst_name,
-                                              &state->bs,
-                                              errp);
-    if (!state->bitmap) {
-        return;
-    }
 
-    merge_source = bdrv_find_dirty_bitmap(state->bs, action->src_name);
-    if (!merge_source) {
-        return;
-    }
-
-    bdrv_merge_dirty_bitmap(state->bitmap, merge_source, &state->backup, errp);
+    state->bitmap = do_block_dirty_bitmap_merge(action->node, action->target,
+                                                action->bitmaps, &state->backup,
+                                                errp);
 }
 
 static void abort_prepare(BlkActionState *common, Error **errp)
@@ -2977,24 +2972,56 @@ 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)
+static BdrvDirtyBitmap *do_block_dirty_bitmap_merge(const char *node,
+                                                    const char *target,
+                                                    strList *bitmaps,
+                                                    HBitmap **backup,
+                                                    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;
+        return NULL;
     }
 
-    src = bdrv_find_dirty_bitmap(bs, src_name);
-    if (!src) {
-        error_setg(errp, "Dirty bitmap '%s' not found", src_name);
-        return;
+    anon = bdrv_create_dirty_bitmap(bs, bdrv_dirty_bitmap_granularity(dst),
+                                    NULL, errp);
+    if (!anon) {
+        return NULL;
+    }
+
+    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);
+            dst = NULL;
+            goto out;
+        }
+
+        bdrv_merge_dirty_bitmap(anon, src, NULL, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            dst = NULL;
+            goto out;
+        }
     }
 
-    bdrv_merge_dirty_bitmap(dst, src, NULL, errp);
+    /* Merge into dst; dst is unchanged on failure. */
+    bdrv_merge_dirty_bitmap(dst, anon, backup, errp);
+
+ out:
+    bdrv_release_dirty_bitmap(bs, anon);
+    return dst;
+}
+
+void qmp_x_block_dirty_bitmap_merge(const char *node, const char *target,
+                                    strList *bitmaps, Error **errp)
+{
+    do_block_dirty_bitmap_merge(node, target, bitmaps, NULL, errp);
 }
 
 BlockDirtyBitmapSha256 *qmp_x_debug_block_dirty_bitmap_sha256(const char *node,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 762000f31f..a153ea4420 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1821,14 +1821,14 @@
 #
 # @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:
@@ -1943,23 +1943,23 @@
 ##
 # @x-block-dirty-bitmap-merge:
 #
-# FIXME: Rename @src_name and @dst_name to src-name and dst-name.
-#
-# Merge @src_name dirty bitmap to @dst_name dirty bitmap. @src_name dirty
-# bitmap is unchanged. On error, @dst_name is unchanged.
+# Merge dirty bitmaps listed in @bitmaps to the @target dirty bitmap.
+# The @bitmaps dirty bitmaps are unchanged.
+# On error, @target is unchanged.
 #
 # Returns: nothing on success
 #          If @node is not a valid block device, DeviceNotFound
-#          If @dst_name or @src_name is not found, GenericError
-#          If bitmaps has different sizes or granularities, GenericError
+#          If any bitmap in @bitmaps or @target is not found, GenericError
+#          If any of the bitmaps have different sizes or granularities,
+#              GenericError
 #
 # Since: 3.0
 #
 # Example:
 #
 # -> { "execute": "x-block-dirty-bitmap-merge",
-#      "arguments": { "node": "drive0", "dst_name": "bitmap0",
-#                     "src_name": "bitmap1" } }
+#      "arguments": { "node": "drive0", "target": "bitmap0",
+#                     "bitmaps": ["bitmap1"] } }
 # <- { "return": {} }
 #
 ##