block: Use CAFs when working with backing chains

Use child access functions when iterating through backing chains so
filters do not break the chain.

In addition, bdrv_find_overlay() will now always return the actual
overlay; that is, it will never return a filter node but only one with a
COW backing file (there may be filter nodes between that node and @bs).

Signed-off-by: Max Reitz <mreitz@redhat.com>

block.c

@@ -4745,9 +4745,9 @@ int bdrv_change_backing_file(BlockDriverState *bs, const char *backing_file,
 }
 
 /*
- * Finds the image layer in the chain that has 'bs' as its backing file.
- *
- * active is the current topmost image.
+ * Finds the first non-filter node above bs in the chain between
+ * active and bs.  The returned node is either an immediate parent of
+ * bs, or there are only filter nodes between the two.
  *
  * Returns NULL if bs is not found in active's image chain,
  * or if active == bs.
@@ -4757,11 +4757,18 @@ int bdrv_change_backing_file(BlockDriverState *bs, const char *backing_file,
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs)
 {
-    while (active && bs != backing_bs(active)) {
-        active = backing_bs(active);
+    bs = bdrv_skip_filters(bs);
+    active = bdrv_skip_filters(active);
+
+    while (active) {
+        BlockDriverState *next = bdrv_backing_chain_next(active);
+        if (bs == next) {
+            return active;
+        }
+        active = next;
     }
 
-    return active;
+    return NULL;
 }
 
 /* Given a BDS, searches for the base layer. */
@@ -4913,9 +4920,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
      * other intermediate nodes have been dropped.
      * If 'top' is an implicit node (e.g. "commit_top") we should skip
      * it because no one inherits from it. We use explicit_top for that. */
-    while (explicit_top && explicit_top->implicit) {
-        explicit_top = backing_bs(explicit_top);
-    }
+    explicit_top = bdrv_skip_implicit_filters(explicit_top);
     update_inherits_from = bdrv_inherits_from_recursive(base, explicit_top);
 
     /* success - we can delete the intermediate states, and link top->base */
@@ -5372,7 +5377,7 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
 bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base)
 {
     while (top && top != base) {
-        top = backing_bs(top);
+        top = bdrv_filter_or_cow_bs(top);
     }
 
     return top != NULL;
@@ -5613,6 +5618,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
     int is_protocol = 0;
     BlockDriverState *curr_bs = NULL;
     BlockDriverState *retval = NULL;
+    BlockDriverState *bs_below;
 
     if (!bs || !bs->drv || !backing_file) {
         return NULL;
@@ -5623,7 +5629,17 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
 
     is_protocol = path_has_protocol(backing_file);
 
-    for (curr_bs = bs; curr_bs->backing; curr_bs = curr_bs->backing->bs) {
+    /*
+     * Being largely a legacy function, skip any filters here
+     * (because filters do not have normal filenames, so they cannot
+     * match anyway; and allowing json:{} filenames is a bit out of
+     * scope).
+     */
+    for (curr_bs = bdrv_skip_filters(bs);
+         bdrv_cow_child(curr_bs) != NULL;
+         curr_bs = bs_below)
+    {
+        bs_below = bdrv_backing_chain_next(curr_bs);
 
         /* If either of the filename paths is actually a protocol, then
          * compare unmodified paths; otherwise make paths relative */
@@ -5631,7 +5647,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
             char *backing_file_full_ret;
 
             if (strcmp(backing_file, curr_bs->backing_file) == 0) {
-                retval = curr_bs->backing->bs;
+                retval = bs_below;
                 break;
             }
             /* Also check against the full backing filename for the image */
@@ -5641,7 +5657,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
                 bool equal = strcmp(backing_file, backing_file_full_ret) == 0;
                 g_free(backing_file_full_ret);
                 if (equal) {
-                    retval = curr_bs->backing->bs;
+                    retval = bs_below;
                     break;
                 }
             }
@@ -5667,7 +5683,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
             g_free(filename_tmp);
 
             if (strcmp(backing_file_full, filename_full) == 0) {
-                retval = curr_bs->backing->bs;
+                retval = bs_below;
                 break;
             }
         }