block: Return depth level during bdrv_is_allocated_above

When checking for allocation across a chain, it's already easy to
count the depth within the chain at which the allocation is found.
Instead of throwing that information away, return it to the caller.
Existing callers only cared about allocated/non-allocated, but having
a depth available will be used by NBD in the next patch.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201027050556.269064-9-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
[eblake: rebase to master]
Signed-off-by: Eric Blake <eblake@redhat.com>

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