block: fix bdrv_replace_node_common

inore_children thing doesn't help to track all propagated permissions
of children we want to ignore. The simplest way to correctly update
permissions is update graph first and then do permission update. In
this case we just referesh permissions for the whole subgraph (in
topological-sort defined order) and everything is correctly calculated
automatically without any ignore_children.

So, refactor bdrv_replace_node_common to first do graph update and then
refresh the permissions.

Test test_parallel_exclusive_write() now pass, so move it out of
debugging "if".

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-18-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -2273,7 +2273,6 @@ static TransactionActionDrv bdrv_replace_child_drv = {
  *
  * Note: real unref of old_bs is done only on commit.
  */
-__attribute__((unused))
 static void bdrv_replace_child_safe(BdrvChild *child, BlockDriverState *new_bs,
                                     Transaction *tran)
 {
@@ -4877,8 +4876,9 @@ static int bdrv_replace_node_common(BlockDriverState *from,
                                     bool auto_skip, Error **errp)
 {
     BdrvChild *c, *next;
-    GSList *list = NULL, *p;
-    uint64_t perm = 0, shared = BLK_PERM_ALL;
+    Transaction *tran = tran_new();
+    g_autoptr(GHashTable) found = NULL;
+    g_autoptr(GSList) refresh_list = NULL;
     int ret;
 
     /* Make sure that @from doesn't go away until we have successfully attached
@@ -4889,7 +4889,12 @@ static int bdrv_replace_node_common(BlockDriverState *from,
     assert(bdrv_get_aio_context(from) == bdrv_get_aio_context(to));
     bdrv_drained_begin(from);
 
-    /* Put all parents into @list and calculate their cumulative permissions */
+    /*
+     * Do the replacement without permission update.
+     * Replacement may influence the permissions, we should calculate new
+     * permissions based on new graph. If we fail, we'll roll-back the
+     * replacement.
+     */
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
         assert(c->bs == from);
         if (!should_update_child(c, to)) {
@@ -4907,36 +4912,24 @@ static int bdrv_replace_node_common(BlockDriverState *from,
                        c->name, from->node_name);
             goto out;
         }
-        list = g_slist_prepend(list, c);
-        perm |= c->perm;
-        shared &= c->shared_perm;
+        bdrv_replace_child_safe(c, to, tran);
     }
 
-    /* Check whether the required permissions can be granted on @to, ignoring
-     * all BdrvChild in @list so that they can't block themselves. */
-    ret = bdrv_check_update_perm(to, NULL, perm, shared, list, errp);
-    if (ret < 0) {
-        bdrv_abort_perm_update(to);
-        goto out;
-    }
+    found = g_hash_table_new(NULL, NULL);
 
-    /* Now actually perform the change. We performed the permission check for
-     * all elements of @list at once, so set the permissions all at once at the
-     * very end. */
-    for (p = list; p != NULL; p = p->next) {
-        c = p->data;
+    refresh_list = bdrv_topological_dfs(refresh_list, found, to);
+    refresh_list = bdrv_topological_dfs(refresh_list, found, from);
 
-        bdrv_ref(to);
-        bdrv_replace_child_noperm(c, to);
-        bdrv_unref(from);
+    ret = bdrv_list_refresh_perms(refresh_list, NULL, tran, errp);
+    if (ret < 0) {
+        goto out;
     }
 
-    bdrv_set_perm(to);
-
     ret = 0;
 
 out:
-    g_slist_free(list);
+    tran_finalize(tran, ret);
+
     bdrv_drained_end(from);
     bdrv_unref(from);
 

tests/unit/test-bdrv-graph-mod.c

@@ -408,10 +408,10 @@ int main(int argc, char *argv[])
                     test_should_update_child);
     g_test_add_func("/bdrv-graph-mod/parallel-perm-update",
                     test_parallel_perm_update);
+    g_test_add_func("/bdrv-graph-mod/parallel-exclusive-write",
+                    test_parallel_exclusive_write);
 
     if (debug) {
-        g_test_add_func("/bdrv-graph-mod/parallel-exclusive-write",
-                        test_parallel_exclusive_write);
         g_test_add_func("/bdrv-graph-mod/append-greedy-filter",
                         test_append_greedy_filter);
     }