1 files changed, 23 insertions, 8 deletions

diff --git a/block/io.c b/block/io.c
index 9918f2499c..ec5e152bb7 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2362,20 +2362,28 @@ bdrv_co_common_block_status_above(BlockDriverState *bs,
                                   int64_t bytes,
                                   int64_t *pnum,
                                   int64_t *map,
-                                  BlockDriverState **file)
+                                  BlockDriverState **file,
+                                  int *depth)
 {
     int ret;
     BlockDriverState *p;
     int64_t eof = 0;
+    int dummy;
 
     assert(!include_base || base); /* Can't include NULL base */
 
+    if (!depth) {
+        depth = &dummy;
+    }
+    *depth = 0;
+
     if (!include_base && bs == base) {
         *pnum = bytes;
         return 0;
     }
 
     ret = bdrv_co_block_status(bs, want_zero, offset, bytes, pnum, map, file);
+    ++*depth;
     if (ret < 0 || *pnum == 0 || ret & BDRV_BLOCK_ALLOCATED || bs == base) {
         return ret;
     }
@@ -2392,6 +2400,7 @@ bdrv_co_common_block_status_above(BlockDriverState *bs,
     {
         ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
                                    file);
+        ++*depth;
         if (ret < 0) {
             return ret;
         }
@@ -2450,7 +2459,7 @@ int bdrv_block_status_above(BlockDriverState *bs, BlockDriverState *base,
                             int64_t *map, BlockDriverState **file)
 {
     return bdrv_common_block_status_above(bs, base, false, true, offset, bytes,
-                                          pnum, map, file);
+                                          pnum, map, file, NULL);
 }
 
 int bdrv_block_status(BlockDriverState *bs, int64_t offset, int64_t bytes,
@@ -2478,7 +2487,7 @@ int coroutine_fn bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset,
     }
 
     ret = bdrv_common_block_status_above(bs, NULL, false, false, offset,
-                                         bytes, &pnum, NULL, NULL);
+                                         bytes, &pnum, NULL, NULL, NULL);
 
     if (ret < 0) {
         return ret;
@@ -2495,7 +2504,7 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
 
     ret = bdrv_common_block_status_above(bs, bs, true, false, offset,
                                          bytes, pnum ? pnum : &dummy, NULL,
-                                         NULL);
+                                         NULL, NULL);
     if (ret < 0) {
         return ret;
     }
@@ -2505,8 +2514,9 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
 /*
  * Given an image chain: ... -> [BASE] -> [INTER1] -> [INTER2] -> [TOP]
  *
- * Return 1 if (a prefix of) the given range is allocated in any image
- * between BASE and TOP (BASE is only included if include_base is set).
+ * Return a positive depth if (a prefix of) the given range is allocated
+ * in any image between BASE and TOP (BASE is only included if include_base
+ * is set).  Depth 1 is TOP, 2 is the first backing layer, and so forth.
  * BASE can be NULL to check if the given offset is allocated in any
  * image of the chain.  Return 0 otherwise, or negative errno on
  * failure.
@@ -2523,13 +2533,18 @@ int bdrv_is_allocated_above(BlockDriverState *top,
                             bool include_base, int64_t offset,
                             int64_t bytes, int64_t *pnum)
 {
+    int depth;
     int ret = bdrv_common_block_status_above(top, base, include_base, false,
-                                             offset, bytes, pnum, NULL, NULL);
+                                             offset, bytes, pnum, NULL, NULL,
+                                             &depth);
     if (ret < 0) {
         return ret;
     }
 
-    return !!(ret & BDRV_BLOCK_ALLOCATED);
+    if (ret & BDRV_BLOCK_ALLOCATED) {
+        return depth;
+    }
+    return 0;
 }
 
 int coroutine_fn