From d38d7eb8a5e78ecc1906e763f59356a0b26a8b53 Mon Sep 17 00:00:00 2001
From: Max Reitz
Date: Wed, 12 Jun 2019 15:06:37 +0200
Subject: block: Add chain helper functions

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

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c                   | 62 +++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h |  3 +++
 2 files changed, 65 insertions(+)

diff --git a/block.c b/block.c
index 9f866e8676..b162142609 100644
--- a/block.c
+++ b/block.c
@@ -7034,3 +7034,65 @@ BdrvChild *bdrv_primary_child(BlockDriverState *bs)
 
     return found;
 }
+
+static BlockDriverState *bdrv_do_skip_filters(BlockDriverState *bs,
+                                              bool stop_on_explicit_filter)
+{
+    BdrvChild *c;
+
+    if (!bs) {
+        return NULL;
+    }
+
+    while (!(stop_on_explicit_filter && !bs->implicit)) {
+        c = bdrv_filter_child(bs);
+        if (!c) {
+            /*
+             * A filter that is embedded in a working block graph must
+             * have a child.  Assert this here so this function does
+             * not return a filter node that is not expected by the
+             * caller.
+             */
+            assert(!bs->drv || !bs->drv->is_filter);
+            break;
+        }
+        bs = c->bs;
+    }
+    /*
+     * Note that this treats nodes with bs->drv == NULL as not being
+     * 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 a filtered child down the chain starting from @bs
+ * (including @bs itself).
+ */
+BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs)
+{
+    return bdrv_do_skip_filters(bs, true);
+}
+
+/*
+ * Return the first BDS that does not have a filtered child down the
+ * chain starting from @bs (including @bs itself).
+ */
+BlockDriverState *bdrv_skip_filters(BlockDriverState *bs)
+{
+    return bdrv_do_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_filters(bdrv_cow_bs(bdrv_skip_filters(bs)));
+}
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f280a95b26..8205ccaa62 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -1394,6 +1394,9 @@ BdrvChild *bdrv_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_primary_child(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs);
 
 static inline BlockDriverState *child_bs(BdrvChild *child)
 {
-- 
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