[PATCH v3 04/15] block: Add chain helper functions

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

From: Max Reitz <mreitz@redhat.com>

Add some helper functions for skipping filters in a chain of block
nodes.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c                   | 55 +++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h |  3 +++
 2 files changed, 58 insertions(+)

diff --git a/block.c b/block.c
index b2aae2e..5b4ebfe 100644
--- a/block.c
+++ b/block.c
@@ -6863,3 +6863,58 @@ BdrvChild *bdrv_primary_child(BlockDriverState *bs)
 {
     return bdrv_filtered_rw_child(bs) ?: bs->file;
 }
+
+static BlockDriverState *bdrv_skip_filters(BlockDriverState *bs,
+                                           bool stop_on_explicit_filter)
+{
+    BdrvChild *filtered;
+
+    if (!bs) {
+        return NULL;
+    }
+
+    while (!(stop_on_explicit_filter && !bs->implicit)) {
+        filtered = bdrv_filtered_rw_child(bs);
+        if (!filtered) {
+            break;
+        }
+        bs = filtered->bs;
+    }
+    /*
+     * Note that this treats nodes with bs->drv == NULL as not being
+     * R/W filters (bs->drv == NULL should be replaced by something
+     * else anyway).
+     * The advantage of this behavior is that this function will thus
+     * always return a non-NULL value (given a non-NULL @bs).
+     */
+
+    return bs;
+}
+
+/*
+ * Return the first BDS that has not been added implicitly or that
+ * does not have an RW-filtered child down the chain starting from @bs
+ * (including @bs itself).
+ */
+BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs)
+{
+    return bdrv_skip_filters(bs, true);
+}
+
+/*
+ * Return the first BDS that does not have an RW-filtered child down
+ * the chain starting from @bs (including @bs itself).
+ */
+BlockDriverState *bdrv_skip_rw_filters(BlockDriverState *bs)
+{
+    return bdrv_skip_filters(bs, false);
+}
+
+/*
+ * For a backing chain, return the first non-filter backing image of
+ * the first non-filter image.
+ */
+BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs)
+{
+    return bdrv_skip_rw_filters(bdrv_filtered_cow_bs(bdrv_skip_rw_filters(bs)));
+}
diff --git a/include/block/block_int.h b/include/block/block_int.h
index dca59e9..86f7666 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -1347,6 +1347,9 @@ BdrvChild *bdrv_filtered_child(BlockDriverState *bs);
 BdrvChild *bdrv_metadata_child(BlockDriverState *bs);
 BdrvChild *bdrv_storage_child(BlockDriverState *bs);
 BdrvChild *bdrv_primary_child(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_rw_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs);
 
 static inline BlockDriverState *child_bs(BdrvChild *child)
 {
-- 
1.8.3.1