[PULL,10/12] block: Return depth level during bdrv_is_allocated_above

diff --git a/block/coroutines.h b/block/coroutines.h
index 1cb3128b942c..4cfb4946e65e 100644
--- a/block/coroutines.h
+++ b/block/coroutines.h
@@ -47,7 +47,8 @@  bdrv_co_common_block_status_above(BlockDriverState *bs,
                                   int64_t bytes,
                                   int64_t *pnum,
                                   int64_t *map,
-                                  BlockDriverState **file);
+                                  BlockDriverState **file,
+                                  int *depth);
 int generated_co_wrapper
 bdrv_common_block_status_above(BlockDriverState *bs,
                                BlockDriverState *base,
@@ -57,7 +58,8 @@  bdrv_common_block_status_above(BlockDriverState *bs,
                                int64_t bytes,
                                int64_t *pnum,
                                int64_t *map,
-                               BlockDriverState **file);
+                               BlockDriverState **file,
+                               int *depth);

 int coroutine_fn bdrv_co_readv_vmstate(BlockDriverState *bs,
                                        QEMUIOVector *qiov, int64_t pos);
diff --git a/block/io.c b/block/io.c
index 02528b3823fe..7751cdb81948 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2349,20 +2349,28 @@  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;
     }
@@ -2379,6 +2387,7 @@  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;
         }
@@ -2437,7 +2446,7 @@  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,
@@ -2455,7 +2464,7 @@  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;
     }
@@ -2465,8 +2474,9 @@  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.
@@ -2483,13 +2493,18 @@  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
diff --git a/block/commit.c b/block/commit.c
index 1e85c306cc41..71db7ba7472e 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -156,7 +156,7 @@  static int coroutine_fn commit_run(Job *job, Error **errp)
         /* Copy if allocated above the base */
         ret = bdrv_is_allocated_above(blk_bs(s->top), s->base_overlay, true,
                                       offset, COMMIT_BUFFER_SIZE, &n);
-        copy = (ret == 1);
+        copy = (ret > 0);
         trace_commit_one_iteration(s, offset, n, ret);
         if (copy) {
             assert(n < SIZE_MAX);
diff --git a/block/mirror.c b/block/mirror.c
index 26acf4af6fb7..8e1ad6eceb57 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -846,7 +846,7 @@  static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
         }

         assert(count);
-        if (ret == 1) {
+        if (ret > 0) {
             bdrv_set_dirty_bitmap(s->dirty_bitmap, offset, count);
         }
         offset += count;
diff --git a/block/stream.c b/block/stream.c
index 8ce6729a33da..236384f2f739 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -167,7 +167,7 @@  static int coroutine_fn stream_run(Job *job, Error **errp)
                 n = len - offset;
             }

-            copy = (ret == 1);
+            copy = (ret > 0);
         }
         trace_stream_one_iteration(s, offset, n, ret);
         if (copy) {