block: Use bdrv_filter_(bs|child) where obvious

Places that use patterns like

    if (bs->drv->is_filter && bs->file) {
        ... something about bs->file->bs ...
    }

should be

    BlockDriverState *filtered = bdrv_filter_bs(bs);
    if (filtered) {
        ... something about @filtered ...
    }

instead.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/block/io.c b/block/io.c
index ad3a51ed53..01e3477a77 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3309,6 +3309,7 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
                                   Error **errp)
 {
     BlockDriverState *bs = child->bs;
+    BdrvChild *filtered;
     BlockDriver *drv = bs->drv;
     BdrvTrackedRequest req;
     int64_t old_size, new_bytes;
@@ -3360,6 +3361,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
         goto out;
     }
 
+    filtered = bdrv_filter_child(bs);
+
     /*
      * If the image has a backing file that is large enough that it would
      * provide data for the new area, we cannot leave it unallocated because
@@ -3392,8 +3395,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
             goto out;
         }
         ret = drv->bdrv_co_truncate(bs, offset, exact, prealloc, flags, errp);
-    } else if (bs->file && drv->is_filter) {
-        ret = bdrv_co_truncate(bs->file, offset, exact, prealloc, flags, errp);
+    } else if (filtered) {
+        ret = bdrv_co_truncate(filtered, offset, exact, prealloc, flags, errp);
     } else {
         error_setg(errp, "Image format driver does not support resize");
         ret = -ENOTSUP;