block: Iterate over children in refresh_limits

Instead of looking at just bs->file and bs->backing, we should look at
all children that could end up receiving forwarded requests.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

block/io.c

@@ -135,6 +135,8 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src)
 void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     BlockDriver *drv = bs->drv;
+    BdrvChild *c;
+    bool have_limits;
     Error *local_err = NULL;
 
     memset(&bs->bl, 0, sizeof(bs->bl));
@@ -149,14 +151,21 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
                                 drv->bdrv_co_preadv_part) ? 1 : 512;
 
     /* Take some limits from the children as a default */
-    if (bs->file) {
-        bdrv_refresh_limits(bs->file->bs, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
-            return;
+    have_limits = false;
+    QLIST_FOREACH(c, &bs->children, next) {
+        if (c->role & (BDRV_CHILD_DATA | BDRV_CHILD_FILTERED | BDRV_CHILD_COW))
+        {
+            bdrv_refresh_limits(c->bs, &local_err);
+            if (local_err) {
+                error_propagate(errp, local_err);
+                return;
+            }
+            bdrv_merge_limits(&bs->bl, &c->bs->bl);
+            have_limits = true;
         }
-        bdrv_merge_limits(&bs->bl, &bs->file->bs->bl);
-    } else {
+    }
+
+    if (!have_limits) {
         bs->bl.min_mem_alignment = 512;
         bs->bl.opt_mem_alignment = qemu_real_host_page_size;
 
@@ -164,15 +173,6 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
         bs->bl.max_iov = IOV_MAX;
     }
 
-    if (bs->backing) {
-        bdrv_refresh_limits(bs->backing->bs, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
-            return;
-        }
-        bdrv_merge_limits(&bs->bl, &bs->backing->bs->bl);
-    }
-
     /* Then let the driver override it */
     if (drv->bdrv_refresh_limits) {
         drv->bdrv_refresh_limits(bs, errp);